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Bruce Momjian authoredBruce Momjian authored
internals.ps 626.06 KiB
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% @@psencodingfile@{
% author = "S. Rahtz, P. MacKay, Alan Jeffrey, B. Horn, K. Berry",
% version = "0.6",
% date = "22 June 1996",
% filename = "8r.enc",
% email = "kb@@mail.tug.org",
% address = "135 Center Hill Rd. // Plymouth, MA 02360",
% codetable = "ISO/ASCII",
% checksum = "119 662 4424",
% docstring = "Encoding for TrueType or Type 1 fonts to be used with TeX."
% @}
%
% Idea is to have all the characters normally included in Type 1 fonts
% available for typesetting. This is effectively the characters in Adobe
% Standard Encoding + ISO Latin 1 + extra characters from Lucida.
%
% Character code assignments were made as follows:
%
% (1) the Windows ANSI characters are almost all in their Windows ANSI
% positions, because some Windows users cannot easily reencode the
% fonts, and it makes no difference on other systems. The only Windows
% ANSI characters not available are those that make no sense for
% typesetting -- rubout (127 decimal), nobreakspace (160), softhyphen
% (173). quotesingle and grave are moved just because it's such an
% irritation not having them in TeX positions.
%
% (2) Remaining characters are assigned arbitrarily to the lower part
% of the range, avoiding 0, 10 and 13 in case we meet dumb software.
%
% (3) Y&Y Lucida Bright includes some extra text characters; in the
% hopes that other PostScript fonts, perhaps created for public
% consumption, will include them, they are included starting at 0x12.
%
% (4) Remaining positions left undefined are for use in (hopefully)
% upward-compatible revisions, if someday more characters are generally
% available.
%
% (5) hyphen appears twice for compatibility with both ASCII and Windows.
%
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% These are the only two remaining unencoded characters, so may as
% well include them.
/Zcaron /zcaron
% 0x10
/caron /dotlessi
% (unusual TeX characters available in, e.g., Lucida Bright)
/dotlessj /ff /ffi /ffl
/.notdef /.notdef /.notdef /.notdef
/.notdef /.notdef /.notdef /.notdef
% very contentious; it's so painful not having quoteleft and quoteright
% at 96 and 145 that we move the things normally found there down to here.
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% 0x20 (ASCII begins)
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/dollar /percent /ampersand /quoteright
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% 0x30
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% 0x70
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% 0x90
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% 0xA0
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% 0xD0
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f(of)g(V)n(iew)778 b(26)273 2860 y Ft(2.1)52 b(A)13 b(Short)e(History)h
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3552 y(5)p eop
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10 9 bop 270 60 a Ft(10)1351 b Fm(CHAPTER)14 b(1.)28
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1084 y(of)h(a)i(part.)345 1184 y Fo(\017)25 b Ft(SELLS)12
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1391 y Fr(SUPPLIER)88 b(SNO)30 b(|)60 b(SNAME)f(|)h(CITY)178
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b(2)60 b(|)g(4)718 1690 y(4)g(|)g(Blake)f(|)30 b(Rome)477
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1870 y(PART)208 b(PNO)30 b(|)60 b(PNAME)f(|)h(PRICE)417
b(4)60 b(|)g(3)659 1929 y(-----+---------+---------)355
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2627 y(we)f(will)e(study)i(the)f(theory)g(of)g(the)g(relational)g
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Fk(;)g(b)p Fl(\))p Fk(;)h Fl(\(1)p Fk(;)f(c)p Fl(\))p
Fo(g)p Ft(.)198 420 y Fn(De\002nition)j(1.2)25 b Ft(A)13
b(Relation)g(is)h(an)o(y)g(subset)f(of)g(the)h(Cartesian)f(product)g
(of)f(one)i(or)f(more)f(domains:)198 480 y Fk(R)i Fo(\022)e
Fk(D)342 487 y Fg(1)376 480 y Fo(\002)f Fk(D)467 487
y Fg(2)500 480 y Fo(\002)g Fk(:)d(:)g(:)j Fo(\002)g Fk(D)710
487 y Ff(k)198 584 y Ft(F)o(or)g(e)o(xample)h Fo(f)p
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Fl(\))p Fk(;)g Fl(\(1)p Fk(;)g(a)p Fl(\))p Fo(g)15 b
Ft(is)d(a)g(relation,)f(it)g(is)h(in)g(fact)f(a)g(subset)i(of)e
Fk(D)1635 591 y Fg(1)1666 584 y Fo(\002)d Fk(D)1754 591
y Fg(2)1788 584 y Ft(mentioned)198 644 y(abo)o(v)o(e.)15
b(The)10 b(members)g(of)f(a)h(relation)e(are)i(called)f(tuples.)15
b(Each)10 b(relation)f(of)g(some)h(Cartesian)g(product)198
703 y Fk(D)239 710 y Fg(1)273 703 y Fo(\002)g Fk(D)363
710 y Fg(2)397 703 y Fo(\002)h Fk(:)d(:)g(:)j Fo(\002)g
Fk(D)607 710 y Ff(k)644 703 y Ft(is)i(said)g(to)f(ha)o(v)o(e)g(arity)g
Fk(k)i Ft(and)f(is)f(therefore)f(a)i(set)g(of)f Fk(k)r
Ft(-tuples.)273 764 y(A)j(relation)f(can)h(be)f(vie)o(wed)h(as)g(a)g
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Fp(The)f(sup-)198 824 y(pliers)j(and)g(parts)h(database)p
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(w)e(and)i(e)o(v)o(ery)f(column)198 884 y(corresponds)c(to)h(one)f
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(attrib)o(utes\))f(to)i(the)f(columns)198 944 y(leads)g(to)f(the)g
(de\002nition)g(of)g(a)g Fp(r)n(elation)h(sc)o(heme)p
Ft(.)198 1070 y Fn(De\002nition)e(1.3)25 b Ft(A)12 b
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(attrib)o(utes)g Fo(f)p Fk(A)1507 1077 y Fg(1)1529 1070
y Fk(;)c(A)1588 1077 y Fg(2)1611 1070 y Fk(;)g(:)g(:)g(:)h(;)f(A)1759
1077 y Ff(k)1784 1070 y Fo(g)p Ft(.)15 b(There)e(is)198
1130 y(a)h(domain)g Fk(D)439 1137 y Ff(i)470 1130 y Ft(for)g(each)g
(attrib)o(ute)g Fk(A)865 1137 y Ff(i)882 1130 y Fk(;)8
b Fl(1)17 b Fo(\024)g Fk(i)g Fo(\024)g Fk(k)f Ft(where)e(the)g(v)o
(alues)h(of)f(the)g(attrib)o(utes)f(are)i(taken)198 1189
y(from.)g(W)l(e)d(often)g(write)g(a)h(relation)e(scheme)i(as)g
Fk(R)p Fl(\()p Fk(A)1139 1196 y Fg(1)1162 1189 y Fk(;)8
b(A)1221 1196 y Fg(2)1244 1189 y Fk(;)g(:)g(:)g(:)h(;)f(A)1392
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b Ft(A)15 b Fp(r)n(elation)g(sc)o(heme)i Ft(is)e(just)h(a)f(kind)g(of)g
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(a)198 1353 y Fp(r)n(elation)h(sc)o(heme)p Ft(.)26 b(The)17
b Fp(r)n(elation)e Ft(consists)i(of)e(tuples)h(\(and)f(can)h(therefore)
e(be)i(vie)o(wed)f(as)i(a)f(table\))198 1413 y(not)c(so)h(the)f
Fp(r)n(elation)h(sc)o(heme)p Ft(.)198 1552 y Fn(Domains)g(vs.)j(Data)c
(T)l(ypes)198 1647 y Ft(W)l(e)j(often)g(talked)f(about)h
Fp(domains)g Ft(in)g(the)g(last)g(section.)25 b(Recall)15
b(that)g(a)g(domain)g(is,)h(formally)m(,)f(just)198 1707
y(a)f(set)g(of)f(v)o(alues)h(\(e.g.,)h(the)e(set)h(of)g(inte)o(gers)f
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(systems)198 1767 y(we)f(often)f(talk)g(of)g Fp(data)h(types)g
Ft(instead)g(of)f(domains.)k(When)d(we)g(de\002ne)f(a)h(table)g(we)f
(ha)o(v)o(e)h(to)g(make)f(a)198 1827 y(decision)j(about)f(which)g
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(to)g(decide)f(which)g(kind)h(of)198 1886 y(data)f(is)f(going)g(to)h
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1946 y(table)g(SUPPLIER)f(will)g(be)h(character)f(strings,)h(whereas)g
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2006 y(by)f(assigning)f(a)h Fp(data)g(type)f Ft(to)h(each)g(attrib)o
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b(ARCHAR\(20\))9 b(\(this)198 2066 y(is)14 b(the)f(SQL)h(type)f(for)g
(character)g(strings)g(of)h(length)f Fo(\024)g Ft(20\),)h(the)f(type)h
(of)f(SNO)g(will)g(be)g(INTEGER.)198 2125 y(W)n(ith)i(the)h(assignment)
g(of)f(a)g Fp(data)h(type)f Ft(we)h(also)g(ha)o(v)o(e)g(selected)g(a)g
(domain)f(for)f(an)i(attrib)o(ute.)25 b(The)198 2185
y(domain)12 b(of)g(SN)n(AME)i(is)f(the)f(set)h(of)f(all)h(character)f
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(what)g(to)g(do)198 2652 y(with)g(all)f(these)i(tables)f(to)g(retrie)o
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b(F)o(or)14 b(e)o(xample)h(somebody)198 2712 y(could)i(ask)g(for)f(the)
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b(kinds)h(of)g(notations)g(for)g(e)o(xpressing)g(operations)g(on)h
(relations)f(ha)o(v)o(e)g(been)h(de\002ned:)273 2875
y Fo(\017)25 b Ft(The)14 b Fp(Relational)f(Algebr)o(a)g
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Fp(Relational)f(Calculus)h Ft(which)f(is)h(a)g(logical)g(notation,)f
(where)h(queries)f(are)h(e)o(xpressed)g(by)323 3098 y(formulating)d
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%%Page: 14 14
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Fp(The)g(suppliers)g(and)f(parts)h(database)270 2075
y Ft(again)c(leads)h(to)f(the)g(same)h(result)f(as)h(in)g(e)o(xample)f
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(algebra)h(can)g(also)g(be)g(formulated)e(using)i(the)270
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15 14 bop 198 60 a Fm(1.3.)29 b(THE)13 b(SQL)f(LANGU)n(A)n(GE)1160
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(algebra)h(nor)g(in)g(relational)g(calculus.)273 552
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1404 y([,)i(...)f([,)h(<table_name_n>)e([t_alias_n]]])288
1464 y([WHERE)h(condition])288 1524 y([GROUP)g(BY)h(<name_of_attr_i>)
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1643 y([{UNION)f(|)h(INTERSECT)e(|)i(EXCEPT})f(SELECT)h(...])288
1703 y([ORDER)f(BY)h(<name_of_attr_i>)e([ASC|DESC])587
1763 y([,)h(...)h([,)f(<name_of_attr_j>)g([ASC|DESC]]]];)198
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b(TABLE)g(SUPPLIER)676 2290 y(\(SNO)89 b(INTEGER,)706
2350 y(SNAME)29 b(VARCHAR\(20\),)706 2410 y(CITY)59 b(VARCHAR\(20\)\);)
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2888 y(\(SNO)h(INTEGER,)706 2948 y(PNO)g(INTEGER\);)198
3092 y Fn(Data)12 b(T)l(ypes)h(in)f(SQL)198 3189 y Ft(The)h(follo)o
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22 21 bop 270 60 a Ft(22)1354 b Fm(CHAPTER)14 b(1.)25
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(string)g(of)g(maximum)f(length)h Fk(n)p Ft(.)270 768
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(up)f(access)i(to)e(a)g(relation.)21 b(If)14 b(a)g(relation)g
Fk(R)g Ft(has)h(an)f(inde)o(x)h(on)f(attrib)o(ute)270
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Fk(t)g Ft(ha)o(ving)f Fk(t)p Fl(\()p Fk(A)p Fl(\))22
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1131 y Fr(CREATE)29 b(INDEX)g(<index_name>)360 1190 y(ON)g
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1452 y Fr(CREATE)29 b(INDEX)g(I)360 1512 y(ON)g(SUPPLIER)g(\(SNAME\);)
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(are)g(an)h(increased)g(speed.)270 1852 y Fn(Cr)o(eate)f(V)n(iew)270
1945 y Ft(A)i(vie)o(w)f(may)h(be)g(re)o(garded)f(as)h(a)g
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270 2304 y(stored)c Fp(base)g(tables)h Ft(in)e(order)h(to)g
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2573 y Fr(CREATE)29 b(VIEW)g(<view_name>)360 2632 y(AS)g(<select_stmt>)
270 2722 y Ft(where)10 b Fk(<)p Fr(select)p 624 2722
15 2 v 17 w(stmt)p Fk(>)40 b Ft(is)11 b(a)g(v)o(alid)g(select)g
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(in)h(the)270 2842 y Fp(system)e(catalogs)f Ft(and)g(is)h(e)o(x)o
(ecuted)g(whene)o(v)o(er)f(a)h(query)f(against)g(the)g(vie)o(w)g(is)h
(made.)270 2954 y Fn(Example)g(1.14)25 b Ft(Let)16 b(the)g(follo)o
(wing)f(vie)o(w)h(de\002nition)f(be)h(gi)o(v)o(en)g(\(we)g(use)g(the)g
(tables)h(from)e(\002gure)270 3014 y(1.1)e Fp(The)f(suppliers)h(and)f
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23 22 bop 198 60 a Fm(1.3.)26 b(THE)13 b(SQL)f(LANGU)n(A)n(GE)1163
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338 y Fr(SELECT)29 b(*)288 397 y(FROM)g(London_Suppliers)288
457 y(WHERE)g(P.PNAME)g(=)h('Screw';)198 560 y Ft(will)12
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b(Data)15 b(Manipulation)198 2345 y Fn(Insert)e(Into)198
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2603 y Fr(INSERT)29 b(INTO)g(<table_name>)g(\(<name_of_attr_1>)1065
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24 23 bop 270 60 a Ft(24)1351 b Fm(CHAPTER)14 b(1.)28
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25 24 bop 198 60 a Fm(1.3.)29 b(THE)13 b(SQL)f(LANGU)n(A)n(GE)1160
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38 37 bop 270 60 a Ft(38)310 b Fm(CHAPTER)14 b(2.)25
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39 38 bop 198 60 a Fm(2.5.)29 b(SOME)12 b(OF)h(POSTGRESQL)-5
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1477 y(function)13 b Ft(command)h(in)f(the)h(same)h(way)e(we)h(did)g
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1657 y(of)24 b(the)g(commands)g Fr(insert)g Ft(and)g
Fr(update)g Ft(af)o(fecting)f(the)h(table)g Fr(supplier)p
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(ecution)h(of)f(function)f Fr(trigf\(\))p Ft(.)258 1860
y Fr(testdb=>)29 b(create)g(function)g(trigf\(\))g(returns)g(opaque)258
1920 y(testdb->)g(as)g('/<where_ever_you_put_it/trigger.so')258
1980 y(testdb->)g(language)g('c';)258 2039 y(CREATE)258
2099 y(testdb=>)g(create)g(trigger)g(tbefore)258 2159
y(testdb->)g(before)g(insert)g(or)h(update)f(on)h(supplier)258
2219 y(testdb->)f(for)g(each)h(row)f(execute)g(procedure)g(trigf\(\);)
258 2278 y(CREATE)258 2338 y(testdb=>)198 2422 y Ft(No)o(w)14
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20 b(If)13 b(the)h(v)o(alue)g(for)f Fr(sno)g Ft(is)i(greater)e(than)198
2482 y(zero)f(the)h Fr(insert)e Ft(and)i Fr(update)e
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2625 y(testdb->)g(\(sno,)g(sname,)g(city\))258 2685 y(testdb->)g
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3283 y(testdb->)f(where)g(sname)g(=)h('Adams';)258 3342
y(ERROR:)59 b(insert/update:)28 b(sno)i(must)f(be)h(a)g(value)f(>)h(0)
258 3402 y(testdb=>)p eop
%%Page: 46 46
46 45 bop 270 60 a Ft(46)307 b Fm(CHAPTER)14 b(2.)28
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Ft(and)h Fr(executor)g Ft(of)270 507 y(PostgreSQL)12
b(\(refer)f(to)h(chapter)g(3)h Fp(P)l(ostgr)n(eSQL)g(fr)n(om)f(the)g
(Pr)n(ogr)o(ammer')n(s)i(P)l(oint)e(of)g(V)l(ie)o(w)p
Ft(\).)270 626 y(The)h(set)g(of)f(functions)g(of)f(SPI)h(can)g(be)h(di)
o(vided)f(into)g(the)g(follo)o(wing)f(parts:)345 724
y Fo(\017)25 b Ft(Interface)11 b(Functions:)17 b(These)d(functions)e
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784 y(backend.)i(Whene)o(v)o(er)c(you)h(want)g(to)f(e)o(x)o(ecute)i(a)f
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844 y(you)g(will)g(ha)o(v)o(e)g(to)h(connect)f(to)g(a)h(backend)f(by)g
Fr(SPI)p 1314 844 15 2 v 18 w(connect\(\))p Ft(.)454
943 y Fn(\226)25 b Fr(SPI)p 597 943 V 18 w(connect\(\))11
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1022 y Fn(\226)25 b Fr(SPI)p 597 1022 V 18 w(finish\(\))11
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b Ft(takes)g(a)h(character)f(string)h(containing)f(a)g(SQL)h(query)f
(and)h(a)g(number)504 1160 y Fr(tcount)11 b Ft(as)h(ar)o(guments)f(and)
g(e)o(x)o(ecutes)h(the)g(query)m(.)i(The)e(result)f(can)h(be)f
(obtained)g(from)504 1220 y(the)17 b(global)g(data)g(structure)f
Fr(SPI)p 1108 1220 V 18 w(tuptable)g Ft(which)h(is)g(set)h(by)f
Fr(SPI)p 1801 1220 V 18 w(exec\(\))p Ft(.)29 b(If)504
1280 y Fr(tcount)12 b Ft(is)i(zero)e(then)h(the)g(query)f(is)i(e)o(x)o
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1340 y(scan.)27 b(Using)16 b Fr(tcount)f Fk(>)h Ft(0)g(restricts)g(the)
f(number)h(of)f(tuples)h(for)f(which)h(the)g(query)504
1399 y(will)d(be)h(e)o(x)o(ecuted.)21 b(This)14 b(function)f(should)g
(only)h(be)g(called)f(after)g Fr(SPI)p 1786 1399 V 18
w(connect\(\))504 1459 y Ft(has)g(been)f(processed)h(and)g(a)f
(connection)g(has)h(been)g(established.)454 1538 y Fn(\226)25
b Fr(SPI)p 597 1538 V 18 w(prepare\(\))85 b Ft(creates)h(and)g(returns)
f(an)h(e)o(x)o(ecution)g(plan)504 1598 y(\(parser+planner+optimizer\))
23 b(b)o(ut)j(doesn')o(t)g(e)o(x)o(ecute)g(the)g(query)m(.)56
b(\(The)26 b(function)504 1658 y(performs)15 b(the)i(same)f(steps)h(as)
g Fr(SPI)p 1163 1658 V 18 w(exec\(\))f Ft(e)o(xcept)g(that)g(it)g(does)
h(not)f(e)o(x)o(ecute)h(the)504 1717 y(plan.)f(Should)11
b(only)h(be)h(called)f(after)g(a)h(connection)f(has)g(been)h
(established.)454 1796 y Fn(\226)25 b Fr(SPI)p 597 1796
V 18 w(saveplan\(\))10 b Ft(stores)h(a)g(plan)g(prepared)f(by)h
Fr(SPI)p 1518 1796 V 18 w(prepare\(\))f Ft(in)h(safe)g(mem-)504
1856 y(ory)h(protected)g(from)f(freeing)h(by)g Fr(SPI)p
1199 1856 V 17 w(finish\(\))p Ft(.)454 1935 y Fn(\226)25
b Fr(SPI)p 597 1935 V 18 w(execp\(\))12 b Ft(e)o(x)o(ecutes)h(a)g(plan)
f(prepared)g(by)g Fr(SPI)p 1491 1935 V 18 w(prepare\(\))g
Ft(or)g(returned)f(by)504 1995 y Fr(SPI)p 597 1995 V
18 w(saveplan\(\))p Ft(.)345 2094 y Fo(\017)25 b Ft(Interface)8
b(Support)i(Functions:)j(These)f(functions)e(can)g(be)h(used)g(from)e
(within)h(a)g(connected)h(or)395 2153 y(within)g(an)g(unconnected)h
(user)f(de\002ned)h(function.)j(An)c(e)o(xample)h(for)f(the)g(use)h
(from)f(within)g(an)395 2213 y(unconnected)k(function)g(was)h(gi)o(v)o
(en)g(in)f(e)o(xample)h(2.11)g(where)g Fr(SPI)p 1634
2213 V 17 w(getbinval\(\))f Ft(was)395 2273 y(used)h(to)g(deli)o(v)o
(er)g(the)g(v)o(alue)g(of)g(attrib)o(ute)g Fr(sno)g Ft(from)f(the)h(ne)
o(w)g(\(to)g(be)g(inserted\))g(tuple.)27 b(An)395 2333
y(e)o(xample)12 b(for)f(the)h(use)g(from)f(within)g(a)h(connected)g
(function)f(will)h(be)g(gi)o(v)o(en)g(in)f(e)o(xample)h(2.12.)454
2432 y Fn(\226)25 b Fr(SPI)p 597 2432 V 18 w(copytuple\(\))11
b Ft(makes)h(a)h(copy)f(of)f(the)i(tuple)f(gi)o(v)o(en)g(as)h(ar)o
(gument.)454 2510 y Fn(\226)25 b Fr(SPI)p 597 2510 V
18 w(modifytuple\(\))j Ft(modi\002es)i(one)g(or)f(more)h(attrib)o(utes)
f(of)h(a)g(gi)o(v)o(en)g(tu-)504 2570 y(ple.)73 b(The)32
b(ne)o(w)g(v)o(alues)f(for)g(the)g(attrib)o(utes)g(to)g(be)h(changed)g
(are)f(passed)h(to)504 2630 y Fr(SPI)p 597 2630 V 18
w(modifytuple\(\))11 b Ft(as)i(ar)o(guments.)454 2709
y Fn(\226)25 b Fr(SPI)p 597 2709 V 18 w(fnumber\(\))11
b Ft(takes)h(the)g(description)g(of)g(a)g(tuple)g(and)g(the)h
Fp(name)f Ft(of)g(an)g(attrib)o(ute)504 2769 y(as)h(ar)o(guments)f(and)
h(returns)e(the)i Fp(number)f Ft(of)g(the)h(attrib)o(ute.)454
2848 y Fn(\226)25 b Fr(SPI)p 597 2848 V 18 w(fname\(\))13
b Ft(takes)g(the)g(description)g(of)h(a)f(tuple)g(and)h(the)f
Fp(number)h Ft(of)f(an)h(attrib)o(ute)504 2907 y(as)f(ar)o(guments)f
(and)h(returns)e(the)i Fp(name)f Ft(of)g(the)g(attrib)o(ute.)454
2986 y Fn(\226)25 b Fr(SPI)p 597 2986 V 18 w(getvalue\(\))13
b Ft(takes)g(the)h(description)g(of)f(a)h(tuple,)h(the)e(tuple)h(and)g
(the)g(number)504 3046 y(of)k(an)g(attrib)o(ute)f(as)i(ar)o(guments)e
(and)i(returns)e(a)h Fp(string)h(r)n(epr)n(esentation)g
Ft(of)e(the)h(gi)o(v)o(en)504 3106 y(attrib)o(ute')m(s)12
b(v)o(alue.)454 3185 y Fn(\226)25 b Fr(SPI)p 597 3185
V 18 w(getbinval\(\))10 b Ft(takes)h(the)g(description)g(of)f(a)i
(tuple,)f(the)h(tuple)e(and)i(the)f(number)504 3244 y(of)h(an)h(attrib)
o(ute)e(as)i(ar)o(guments)f(and)g(returns)g(the)h(binary)e(v)o(alue)h
(of)g(the)h(gi)o(v)o(en)f(attrib)o(ute.)454 3323 y Fn(\226)25
b Fr(SPI)p 597 3323 V 18 w(gettype\(\))11 b Ft(returns)h(a)h(copy)e(of)
h(the)h(type)f(name)g(for)g(the)g(speci\002ed)h(attrib)o(ute.)454
3402 y Fn(\226)25 b Fr(SPI)p 597 3402 V 18 w(gettypeid\(\))11
b Ft(returns)h(the)g(type)g(OID)g(for)g(the)g(speci\002ed)h(attrib)o
(ute.)p eop
%%Page: 47 47
47 46 bop 198 60 a Fm(2.5.)26 b(SOME)12 b(OF)h(POSTGRESQL)-5
b('S)12 b(SPECIAL)h(FEA)-6 b(TURES)14 b(IN)e(DET)-5 b(AIL)343
b Ft(47)382 234 y Fn(\226)25 b Fr(SPI)p 525 234 15 2
v 18 w(getrelname\(\))11 b Ft(returns)h(the)g(name)g(of)g(the)h
(speci\002ed)f(relation.)382 315 y Fn(\226)25 b Fr(SPI)p
525 315 V 18 w(palloc\(\))e Ft(allocates)i(memory)m(.)50
b(In)23 b(contrast)h(to)g Fr(malloc\(\))g Ft(\(normally)432
375 y(used\))15 b(it)g(allocates)h(memory)e(in)h(such)h(a)f(way)g(that)
g(it)g(can)g(be)g(freed)g(automatically)f(by)432 434
y Fr(SPI)p 525 434 V 18 w(finish\(\))p Ft(.)382 515 y
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b Ft(frees)i(memory)e(allocated)h(by)h Fr(SPI)p 1397
656 V 17 w(palloc\(\))p Ft(.)198 778 y Fn(Example)g(2.12)25
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Fp(trigger)198 898 y(function)k Fr(trigf)p 531 898 V
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b Ft(get)12 b(the)g(greatest)h(supplier)f(id)g Fr(sno)g
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b Ft(modify)13 b(attrib)o(ute)h Fr(sno)h Ft(of)g(the)f(tuple)h(to)g(be)
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eop
%%Page: 48 48
48 47 bop 270 60 a Ft(48)307 b Fm(CHAPTER)14 b(2.)28
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Ft(W)l(e)13 b(again)f(create)g(the)g(shared)h(library)e
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Fr(select)f Ft(against)h(the)g(table)g Fr(my)p 1936 1091
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51 50 bop 198 608 a Fj(Chapter)26 b(3)198 857 y Fq(P)n(ostgr)n(eSQL)k
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(w)g(within)g(the)g(backend)g(from)198 1564 y(recei)o(ving)i(a)g(query)
g(to)g(sending)h(the)f(results.)198 1729 y Fi(3.1)71
b(The)18 b(W)-5 b(ay)18 b(of)f(a)h(Query)198 1841 y Ft(Here)12
b(we)h(gi)o(v)o(e)f(a)h(short)f(o)o(v)o(ervie)o(w)g(of)g(the)g(stages)h
(a)g(query)f(has)g(to)h(pass)g(in)f(order)g(to)g(obtain)g(a)g(result:)
273 1927 y Fo(\017)25 b Ft(First)14 b(a)h(connection)f(from)g(an)h
(application)f(program)g(to)g(the)h(PostgreSQL)f(serv)o(er)h(has)g(to)g
(be)323 1987 y(established.)g(The)d(application)f(program)f(transmits)i
(a)f(query)g(to)g(the)h(serv)o(er)f(and)g(recei)o(v)o(es)h(the)323
2047 y(results)g(sent)h(back)f(by)h(the)f(serv)o(er)m(.)273
2140 y Fo(\017)25 b Ft(The)17 b Fp(parser)g(stage)f Ft(checks)i(the)e
(query)h(transmitted)f(by)h(the)f(application)h(program)e(\(client\))
323 2200 y(for)c(correct)h(syntax)g(and)h(creates)f(a)h
Fp(query)g(tr)n(ee)p Ft(.)273 2293 y Fo(\017)25 b Ft(The)18
b Fp(r)n(e)o(write)h(system)f Ft(takes)f(the)h Fp(query)g(tr)n(ee)g
Ft(created)g(by)f(the)h Fp(parser)g(stage)f Ft(looks)g(for)g(an)o(y)323
2352 y Fp(rules)11 b Ft(\(stored)g(in)g(the)g Fp(system)h(catalogs)p
Ft(\))e(to)h(apply)f(to)h(the)g Fp(querytr)n(ee)i Ft(and)e(performs)f
(the)h(trans-)323 2412 y(formations)j(gi)o(v)o(en)g(in)h(the)g
Fp(rule)h(bodies)p Ft(.)24 b(One)15 b(application)g(of)f(the)h
Fp(r)n(e)o(write)i(system)f Ft(is)f(gi)o(v)o(en)323 2472
y(in)f(the)g(realization)f(of)h Fp(vie)o(ws)p Ft(.)23
b(Whene)o(v)o(er)14 b(a)g(query)g(against)g(a)g Fp(vie)o(w)h
Ft(\(i.e.)22 b(a)14 b Fp(virtual)g(table)p Ft(\))g(is)323
2532 y(made,)h(the)f Fp(r)n(e)o(write)h(system)g Ft(re)o(writes)f(the)g
(user')m(s)h(query)e(to)h(a)h(query)f(that)g(accesses)i(the)e
Fp(base)323 2592 y(tables)e Ft(gi)o(v)o(en)g(in)g(the)h
Fp(vie)o(w)g(de\002nition)e Ft(instead.)273 2685 y Fo(\017)25
b Ft(The)17 b Fp(planner/optimizer)f Ft(takes)h(the)g(\()p
Fp(r)n(e)o(written)p Ft(\))f Fp(querytr)n(ee)i Ft(and)f(creates)g(a)g
Fp(queryplan)f Ft(that)323 2744 y(will)10 b(be)i(the)f(input)f(to)h
(the)g Fp(e)o(xecutor)p Ft(.)16 b(It)11 b(does)h(so)f(by)g(\002rst)g
(creating)g(all)g(possible)g Fp(paths)g Ft(leading)323
2804 y(to)16 b(the)g(same)h(result.)29 b(\()16 b(F)o(or)g(e)o(xample)h
(if)f(there)g(is)h(an)f(inde)o(x)h(on)f(a)h(relation)f(to)g(be)h
(scanned,)323 2864 y(there)c(are)g(two)g Fp(paths)h Ft(for)f(the)g
(scan.)20 b(One)14 b(possibility)f(is)h(a)g(simple)g(sequential)f(scan)
i(and)e(the)323 2924 y(other)g(possibility)g(is)h(to)f(use)h(the)g
(inde)o(x.\))19 b(Ne)o(xt)14 b(the)f(cost)h(for)f(the)h(e)o(x)o
(ecution)f(of)h(each)g Fp(plan)f Ft(is)323 2984 y(estimated)f(and)g
(the)h(cheapest)g Fp(plan)f Ft(is)g(chosen)h(and)f(handed)h(back.)273
3077 y Fo(\017)25 b Ft(The)14 b Fp(e)o(xecutor)h Ft(recursi)o(v)o(ely)f
(steps)h(through)e(the)h Fp(plan)g(tr)n(ee)h Ft(and)f(retrie)o(v)o(es)g
(tuples)g(in)g(the)h(way)323 3136 y(represented)f(by)g(the)g
Fp(plan)p Ft(.)21 b(The)15 b Fp(e)o(xecutor)g Ft(makes)f(use)h(of)f
(the)g Fp(stor)o(age)h(system)g Ft(while)f(scan-)323
3196 y(ning)i(relations,)j(performs)d Fp(sorts)i Ft(and)f
Fp(joins)p Ft(,)i(e)o(v)o(aluates)e Fp(quali\002cations)g
Ft(and)g(\002nally)g(hands)323 3256 y(back)12 b(the)g(tuples)h(deri)o
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(in)f(more)g(detail)g(to)198 3402 y(gi)o(v)o(e)c(a)h(better)f
(understanding)f(on)i(PostgreSQL)-5 b(')m(s)12 b(internal)g(control)f
(and)i(data)f(structures.)1073 3552 y(51)p eop
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52 51 bop 270 60 a Ft(52)82 b Fm(CHAPTER)14 b(3.)28 b(POSTGRESQL)13
b(FR)n(OM)f(THE)i(PR)n(OGRAMMER'S)f(POINT)f(OF)g(VIEW)270
234 y Fi(3.2)71 b(Ho)o(w)18 b(Connections)f(ar)o(e)g(Established)270
370 y Ft(PostgreSQL)c(is)g(implemented)f(using)h(a)g(simple)g
(\224process)h(per)o(-user\224)e(client/serv)o(er)h(model.)k(In)c(this)
270 430 y(model)k(there)f(is)h(one)g Fp(client)g(pr)n(ocess)h
Ft(connected)f(to)f(e)o(xactly)i(one)e Fp(server)j(pr)n(ocess)p
Ft(.)30 b(As)18 b(we)f(don')o(t)270 490 y(kno)o(w)f Fp(per)h(se)g
Ft(ho)o(w)f(man)o(y)h(connections)g(will)f(be)g(made,)j(we)d(ha)o(v)o
(e)h(to)g(use)g(a)f Fp(master)i(pr)n(ocess)f Ft(that)270
549 y(spa)o(wns)h(a)e(ne)o(w)h Fp(server)h(pr)n(ocess)f
Ft(e)o(v)o(ery)f(time)h(a)f(connection)h(is)f(requested.)29
b(This)17 b Fp(master)g(pr)n(ocess)270 609 y Ft(is)f(called)g
Fr(postmaster)e Ft(and)i(listens)g(at)f(a)h(speci\002ed)g(TCP/IP)f
(port)g(for)g(incoming)g(connections.)270 669 y(Whene)o(v)o(er)e(a)h
(request)f(for)f(a)i(connection)f(is)h(detected)f(the)g
Fr(postmaster)g Ft(process)g(spa)o(wns)i(a)e(ne)o(w)270
729 y Fp(server)i(pr)n(ocess)f Ft(called)g Fr(postgres)p
Ft(.)j(The)d(serv)o(er)g(tasks)g(\()p Fr(postgres)e Ft(processes\))i
(communicate)270 788 y(with)k(each)g(other)f(using)h
Fp(semaphor)n(es)h Ft(and)f Fp(shar)n(ed)h(memory)g Ft(to)e(ensure)h
(data)g(inte)o(grity)f(through-)270 848 y(out)j(concurrent)e(data)i
(access.)40 b(Figure)19 b(3.1)h(illustrates)f(the)h(interaction)f(of)g
(the)h(master)g(process)270 908 y Fr(postmaster)11 b
Ft(the)i(serv)o(er)f(process)h Fr(postgres)e Ft(and)i(a)f(client)h
(application.)345 981 y(The)e(client)g(process)g(can)h(either)e(be)h
(the)g Fr(psql)g Ft(frontend)f(\(for)f Fp(inter)o(active)j
Ft(SQL)f(queries\))f(or)h(an)o(y)270 1041 y(user)f(application)f
(implemented)g(using)h(the)f Fr(libpg)h Ft(library)m(.)j(Note)d(that)f
(applications)h(implemented)270 1100 y(using)i Fr(ecpq)g
Ft(\(i.e.)k(the)d(postgres)f(embedded)g(C)h(compiler\))e(also)i(use)g
(this)f(library)m(.)345 1173 y(Once)e(a)g(connection)f(is)i
(established)f(the)g(client)f(process)i(can)f(send)g(a)g(query)f(to)h
(the)g Fp(bac)o(kend)p Ft(.)15 b(The)270 1233 y(query)f(is)h
(transmitted)e(using)i Fp(plain)f(te)o(xt)p Ft(,)h(i.e.)23
b(there)14 b(is)h(no)f(parsing)g(done)h(in)f(the)h Fp(fr)n(ontend)f
Ft(\(client\).)270 1293 y(The)i(serv)o(er)g Fp(parses)g
Ft(the)g(query)m(,)g(creates)g(an)g Fp(e)o(xecution)f(plan)p
Ft(,)i(e)o(x)o(ecutes)g(the)e Fp(plan)g Ft(and)h(returns)f(the)270
1352 y(retrie)o(v)o(ed)c(tuples)i(to)f(the)g(client)h(by)f
(transmitting)f(them)h(o)o(v)o(er)h(the)f(established)h(connection.)543
2309 y @beginspecial 180 @llx 310 @lly 431 @urx 482 @ury
2510 @rwi @setspecial
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%%EndDocument
@endspecial 595 2973 a(Figure)11 b(3.3:)16 b Fp(Wher)n(eClause)e
Ft(for)e(query)f(of)h(e)o(xample)h(3.1)p eop
%%Page: 56 56
56 55 bop 270 60 a Ft(56)82 b Fm(CHAPTER)14 b(3.)28 b(POSTGRESQL)13
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234 y Ft(Ne)o(xt)k(it)h(is)f(checked)g(if)g(the)g Fp(attrib)o(ute)g
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Fr(SeqScan)g Ft(node)g(of)g(the)g(corresponding)g(subplan.)345
494 y(The)k(list)f(attached)g(to)g(the)h(\002eld)f Fr(mergeclauses)f
Ft(of)g(the)i Fr(MergeJoin)e Ft(node)h(contains)h(in-)270
554 y(formation)e(about)h(the)g Fr(join)30 b(attributes)p
Ft(.)23 b(The)16 b(v)o(alues)g Fl(65000)f Ft(and)g Fl(65001)g
Ft(for)f(the)i Fr(varno)270 613 y Ft(\002elds)f(in)f(the)h
Fr(VAR)g Ft(nodes)g(appearing)f(in)h(the)g Fr(mergeclauses)e
Ft(list)i(\(and)f(also)h(in)g(the)g Fp(tar)n(getlist)p
Ft(\))270 673 y(mean)d(that)g(not)g(the)g(tuples)g(of)g(the)g(current)f
(node)i(should)f(be)g(considered)g(b)o(ut)g(the)g(tuples)g(of)g(the)g
(ne)o(xt)270 733 y(\224deeper\224)g(nodes)h(\(i.e.)j(the)c(top)g(nodes)
h(of)f(the)g(subplans\))h(should)f(be)h(used)f(instead.)345
813 y(Note)i(that)g(e)o(v)o(ery)h Fr(Sort)f Ft(and)g
Fr(SeqScan)g Ft(node)h(appearing)f(in)g(\002gure)g(3.6)g(has)h(got)g(a)
f Fp(tar)n(getlist)270 873 y Ft(b)o(ut)g(because)h(there)g(was)f(not)g
(enough)h(space)g(only)f(the)g(one)h(for)e(the)i Fr(MergeJoin)e
Ft(node)i(could)f(be)270 933 y(dra)o(wn.)345 1013 y(Another)c(task)i
(performed)d(by)i(the)g Fp(planner/optimizer)g Ft(is)h(\002xing)e(the)h
Fp(oper)o(ator)h(ids)f Ft(in)g(the)g Fr(Expr)270 1073
y Ft(and)16 b Fr(Oper)h Ft(nodes.)28 b(As)17 b(mentioned)e(earlier)n(,)
j(PostgreSQL)e(supports)g(a)h(v)o(ariety)e(of)h(dif)o(ferent)f(data)270
1133 y(types)f(and)f(e)o(v)o(en)g(user)h(de\002ned)f(types)g(can)h(be)f
(used.)20 b(T)l(o)13 b(be)h(able)f(to)g(maintain)g(the)g(huge)h(amount)
f(of)270 1193 y(functions)h(and)g(operators)g(it)g(is)h(necessary)g(to)
f(store)h(them)f(in)g(a)h Fp(system)g(table)p Ft(.)22
b(Each)15 b(function)e(and)270 1253 y(operator)e(gets)i(a)g(unique)f
Fp(oper)o(ator)h(id)p Ft(.)j(According)11 b(to)h(the)h(types)f(of)g
(the)h(attrib)o(utes)f(used)g(within)g(the)270 1312 y(quali\002cations)
g(etc.,)h(the)g(appropriate)e Fp(oper)o(ator)i(ids)g
Ft(ha)o(v)o(e)f(to)h(be)f(used.)270 1594 y Fi(3.6)71
b(Executor)270 1745 y Ft(The)12 b Fp(e)o(xecutor)f Ft(takes)g(the)g
Fp(plan)g Ft(handed)g(back)g(by)g(the)g Fp(planner/optimizer)g
Ft(and)g(starts)g(processing)g(the)270 1804 y(top)16
b(node.)27 b(In)15 b(the)h(case)h(of)f(our)f(e)o(xample)i(\(the)e
(query)h(gi)o(v)o(en)g(in)g(e)o(xample)g(3.1\))g(the)g(top)g(node)g(is)
g(a)270 1864 y Fr(MergeJoin)11 b Ft(node.)345 1945 y(Before)i(an)o(y)h
(mer)o(ge)f(can)g(be)h(done)f(two)g(tuples)h(ha)o(v)o(e)g(to)f(be)h
(fetched)f(\(one)g(from)f(each)i(subplan\).)270 2004
y(So)i(the)g Fp(e)o(xecutor)h Ft(recursi)o(v)o(ely)f(calls)g(itself)g
(to)g(process)h(the)f(subplans)h(\(it)e(starts)i(with)f(the)g(subplan)
270 2064 y(attached)10 b(to)g Fr(lefttree)p Ft(\).)j(The)e(ne)o(w)f
(top)f(node)h(\(the)g(top)f(node)h(of)g(the)f(left)h(subplan\))f(is)i
(a)f Fr(SeqScan)270 2124 y Ft(node)19 b(and)f(again)h(a)g(tuple)f(has)h
(to)g(be)g(fetched)f(before)g(the)h(node)f(itself)h(can)f(be)h
(processed.)36 b(The)270 2184 y Fp(e)o(xecutor)13 b Ft(calls)g(itself)f
(recursi)o(v)o(ely)f(another)h(time)g(for)g(the)g(subplan)g(attached)h
(to)f Fr(lefttree)f Ft(of)h(the)270 2244 y Fr(SeqScan)g
Ft(node.)345 2324 y(No)o(w)g(the)g(ne)o(w)g(top)h(node)f(is)h(a)f
Fr(Sort)g Ft(node.)k(As)d(a)g(sort)f(has)h(to)f(be)g(done)h(on)f(the)g
(whole)h Fp(r)n(elation)p Ft(,)270 2384 y(the)18 b Fp(e)o(xecutor)h
Ft(starts)f(fetching)f(tuples)h(from)f(the)h Fr(Sort)g
Ft(node')m(s)g(subplan)g(and)g(sorts)h(them)e(into)h(a)270
2444 y(temporary)13 b(relation)h(\(in)f(memory)h(or)f(a)i(\002le\))e
(when)i(the)f Fr(Sort)g Ft(node)g(is)g(visited)h(for)e(the)h(\002rst)g
(time.)270 2503 y(\(Further)e(e)o(xaminations)i(of)g(the)g
Fr(Sort)f Ft(node)h(will)g(always)f(return)g(just)h(one)g(tuple)g(from)
e(the)i(sorted)270 2563 y(temporary)d Fp(r)n(elation)p
Ft(.\))345 2644 y(Ev)o(ery)k(time)g(the)g(processing)g(of)f(the)h
Fr(Sort)g Ft(node)g(needs)g(a)h(ne)o(w)e(tuple)h(the)g
Fp(e)o(xecutor)h Ft(is)f(recur)o(-)270 2703 y(si)o(v)o(ely)i(called)g
(for)f(the)g Fr(SeqScan)g Ft(node)h(attached)g(as)g(subplan.)29
b(The)17 b Fp(r)n(elation)g Ft(\(internally)e(refer)o(-)270
2763 y(enced)i(by)g(the)f(v)o(alue)h(gi)o(v)o(en)f(in)h(the)f
Fr(scanrelid)g Ft(\002eld\))g(is)h(scanned)g(for)f(the)h(ne)o(xt)g
(tuple.)28 b(If)16 b(the)270 2823 y(tuple)h(satis\002es)h(the)f
(quali\002cation)g(gi)o(v)o(en)g(by)g(the)g(tree)g(attached)h(to)f
Fr(qpqual)g Ft(it)g(is)g(handed)h(back,)270 2883 y(otherwise)12
b(the)h(ne)o(xt)f(tuple)h(is)g(fetched)f(until)g(the)g(quali\002cation)
g(is)h(satis\002ed.)k(If)11 b(the)i(last)g(tuple)f(of)g(the)270
2942 y Fp(r)n(elation)g Ft(has)h(been)g(processed)g(a)f
Fr(NULL)g Ft(pointer)g(is)g(returned.)345 3023 y(After)23
b(a)i(tuple)f(has)h(been)f(handed)h(back)f(by)g(the)h
Fr(lefttree)e Ft(of)h(the)h Fr(MergeJoin)e Ft(the)270
3083 y Fr(righttree)16 b Ft(is)h(processed)g(in)g(the)g(same)g(way)m(.)
28 b(If)17 b(both)f(tuples)h(are)g(present)f(the)h(e)o(x)o(ecutor)g
(pro-)270 3142 y(cesses)d(the)e Fr(MergeJoin)f Ft(node.)16
b(Whene)o(v)o(er)c(a)h(ne)o(w)f(tuple)g(from)f(one)h(of)g(the)g
(subplans)h(is)f(needed)h(a)270 3202 y(recursi)o(v)o(e)g(call)f(to)h
(the)g Fp(e)o(xecutor)h Ft(is)f(performed)e(to)i(obtain)f(it.)18
b(If)12 b(a)h Fp(joined)f Ft(tuple)h(could)g(be)g(created)f(it)270
3262 y(is)h(handed)f(back)g(and)h(one)f(complete)g(processing)h(of)f
(the)g Fp(plan)g(tr)n(ee)h Ft(has)g(\002nished.)345 3342
y(No)o(w)j(the)g(described)g(steps)h(are)f(performed)f(once)h(for)g(e)o
(v)o(ery)g(tuple,)h(until)f(a)g Fr(NULL)g Ft(pointer)g(is)270
3402 y(returned)11 b(for)h(the)g(processing)h(of)f(the)g
Fr(MergeJoin)g Ft(node,)g(indicating)g(that)g(we)h(are)f(\002nished.)p
eop
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61 60 bop 198 60 a Fm(3.6.)29 b(EXECUT)o(OR)1384 b Ft(61)243
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$F2psEnd
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%%EndDocument
@endspecial 681 3120 a(Figure)12 b(3.6:)j Fp(Plan)e
Ft(for)e(query)h(of)g(e)o(xample)h(3.1)p eop
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@endspecial 679 2950 a Ft(Figure)f(3.8:)16 b Fp(Plantr)n(ee)d
Ft(for)e(the)i(query)f(of)g(e)o(xample)g(3.2)p eop
%%Page: 65 65
65 64 bop 198 60 a Fm(3.7.)29 b(THE)13 b(REALIZA)-6 b(TION)14
b(OF)e(THE)h(HA)-7 b(VING)12 b(CLA)m(USE)622 b Ft(65)198
234 y Fn(Executor)198 329 y Ft(The)13 b Fp(e)o(xecutor)f
Ft(uses)h(the)f(function)g Fr(execAgg\(\))f Ft(to)h(e)o(x)o(ecute)g
Fr(AGG)g Ft(nodes.)k(As)d(described)f(earlier)f(it)198
389 y(uses)k(one)g(main)f(function)f Fr(ExecProcNode)h
Ft(which)g(is)h(called)f(recursi)o(v)o(ely)g(to)g(e)o(x)o(ecute)h
(subtrees.)198 449 y(The)e(follo)o(wing)e(steps)i(are)f(performed)f(by)
h Fr(execAgg\(\))p Ft(:)273 552 y Fo(\017)25 b Ft(The)15
b(list)g(attached)h(to)f(the)g(\002eld)g Fr(aggs)f Ft(of)h(the)g
Fr(AGG)g Ft(node)g(is)h(e)o(xamined)f(and)g(for)f(e)o(v)o(ery)h
Fp(ag-)323 612 y(gr)n(e)n(gate)f(function)f Ft(included)h(the)g
Fp(tr)o(ansition)g(functions)f Ft(are)h(fetched)g(from)f(a)h
Fp(function)f(table)p Ft(.)323 671 y(Calculating)f(the)g(v)o(alue)g(of)
g(an)h Fp(aggr)n(e)n(gate)e(function)h Ft(is)h(done)f(using)g(three)g
(functions:)382 775 y Fn(\226)25 b Ft(The)18 b Fp(\002rst)g(tr)o
(ansition)g(function)f Fr(xfn1)g Ft(is)h(called)g(with)g(the)f(current)
g(v)o(alue)g(of)h(the)f(at-)432 835 y(trib)o(ute)c(the)h
Fp(aggr)n(e)n(gate)f(function)g Ft(is)h(applied)f(to)h(and)g(changes)g
(its)g(internal)f(state)h(using)432 895 y(the)e(attrib)o(ute')m(s)g(v)o
(alue)g(gi)o(v)o(en)g(as)h(an)g(ar)o(gument.)382 976
y Fn(\226)25 b Ft(The)e Fp(second)f(tr)o(ansition)g(function)f
Fr(xfn2)h Ft(is)g(called)g(without)f(an)o(y)h(ar)o(guments)g(and)432
1036 y(changes)13 b(its)g(internal)e(state)i(only)f(according)g(to)g
(internal)g(rules.)382 1118 y Fn(\226)25 b Ft(The)13
b Fp(\002nal)g(function)f Fr(finalfn)g Ft(takes)h(the)g(\002nal)f
(states)h(of)g Fr(xfn1)f Ft(and)h Fr(xfn2)f Ft(as)i(ar)o(gu-)432
1178 y(ments)f(and)f(\002nishes)h(the)f Fp(aggr)n(e)n(gation)p
Ft(.)323 1302 y Fn(Example)g(3.3)25 b Ft(Recall)19 b(the)f(functions)g
(necessary)h(to)f(implement)g(the)g Fp(aggr)n(e)n(gate)g(function)323
1362 y Fr(avg)12 b Ft(b)o(uilding)g(the)h(a)o(v)o(erage)g(o)o(v)o(er)f
(all)h(v)o(alues)g(of)f(an)h(attrib)o(ute)f(in)g(a)h(group)f(\(see)h
(section)g(2.5.5)323 1422 y Fp(Extending)f(Aggr)n(e)n(gates)p
Ft(\):)382 1526 y Fn(\226)25 b Ft(The)10 b(\002rst)f(transition)g
(function)g Fr(xfn1)g Ft(has)h(to)f(be)g(a)h(function)f(that)g(takes)g
(the)h(actual)f(v)o(alue)432 1585 y(of)15 b(the)h(attrib)o(ute)e
Fr(avg)h Ft(is)h(applied)f(to)h(as)g(an)f(ar)o(gument)g(and)g(adds)h
(it)f(to)h(the)f(internally)432 1645 y(stored)d(sum)h(of)f(pre)o(vious)
g(calls.)382 1727 y Fn(\226)25 b Ft(The)15 b(second)h(transition)d
(function)h Fr(xfn2)h Ft(only)f(increases)h(an)g(internal)f(counter)g
(e)o(v)o(ery)432 1787 y(time)e(it)g(is)h(called.)382
1868 y Fn(\226)25 b Ft(The)10 b(\002nal)g(function)f
Fr(finalfn)g Ft(di)o(vides)g(the)h(result)g(of)f Fr(xfn1)g
Ft(by)h(the)g(counter)f(of)g Fr(xfn2)432 1928 y Ft(to)j(calculate)h
(the)f(a)o(v)o(erage.)323 2053 y(Note)h(that)h Fr(xfn2)f
Ft(and)h Fr(finalfn)f Ft(may)h(be)f(absent)i(\(e.g.)20
b(for)13 b(the)g Fp(aggr)n(e)n(gate)g(function)g Fr(sum)323
2113 y Ft(which)f(simply)g(sums)h(up)f(all)g(v)o(alues)h(of)f(the)g(gi)
o(v)o(en)g(attrib)o(ute)g(within)f(a)i(group.)323 2232
y Fr(execAgg\(\))25 b Ft(creates)i(an)g(array)f(containing)g(one)h
(entry)f(for)g(e)o(v)o(ery)h Fp(aggr)n(e)n(gate)f(func-)323
2292 y(tion)16 b Ft(found)h(in)g(the)g(list)g(attached)g(to)g(the)g
(\002eld)g Fr(aggs)p Ft(.)30 b(The)18 b(array)e(will)h(hold)g
(information)323 2352 y(needed)25 b(for)f(the)i(e)o(x)o(ecution)f(of)g
(e)o(v)o(ery)g Fp(aggr)n(e)n(gate)g(function)g Ft(\(including)f(the)h
Fp(tr)o(ansition)323 2412 y(functions)12 b Ft(described)g(abo)o(v)o
(e\).)273 2515 y Fo(\017)25 b Ft(The)15 b(follo)o(wing)f(steps)i(are)f
(e)o(x)o(ecuted)h(in)f(a)g(loop)g(as)g(long)g(as)h(there)f(are)g(still)
g(tuples)g(returned)323 2575 y(by)e(the)h(subplan)g(\(i.e.)20
b(as)15 b(long)e(as)i(there)e(are)h(still)g(tuples)g(left)f(in)h(the)g
(current)f(group\).)19 b(When)323 2635 y(there)12 b(are)h(no)g(tuples)g
(left)f(in)h(the)g(group)f(a)h Fr(NULL)g Ft(pointer)f(is)h(returned)f
(indicating)h(the)g(end)g(of)323 2695 y(the)f(group.)382
2798 y Fn(\226)25 b Ft(A)15 b(ne)o(w)f(tuple)h(from)e(the)i(subplan)g
(\(i.e.)22 b(the)15 b Fp(plan)f Ft(attached)h(to)f(the)h(\002eld)f
Fr(lefttree)p Ft(\))432 2858 y(is)e(fetched)f(by)g(recursi)o(v)o(ely)f
(calling)h Fr(ExecProcNode\(\))f Ft(with)h(the)g(subplan)g(as)h(ar)o
(gu-)432 2918 y(ment.)382 3000 y Fn(\226)25 b Ft(F)o(or)14
b(e)o(v)o(ery)g Fp(aggr)n(e)n(gate)f(function)h Ft(\(contained)f(in)h
(the)g(array)g(created)g(before\))f(apply)h(the)432 3059
y(transition)e(functions)h Fr(xfn1)f Ft(and)h Fr(xfn2)f
Ft(to)h(the)g(v)o(alues)g(of)f(the)h(appropriate)f(attrib)o(utes)432
3119 y(of)g(the)g(current)g(tuple.)273 3223 y Fo(\017)25
b Ft(When)13 b(we)g(get)g(here,)g(all)g(tuples)g(of)g(the)g(current)f
(group)g(ha)o(v)o(e)i(been)f(processed)g(and)g(the)g
Fp(tr)o(an-)323 3283 y(sition)18 b(functions)h Ft(of)g(all)g
Fp(aggr)n(e)n(gate)g(functions)f Ft(ha)o(v)o(e)i(been)f(applied)g(to)g
(the)g(v)o(alues)g(of)g(the)323 3342 y(attrib)o(utes.)c(W)l(e)d(are)g
(no)o(w)g(ready)f(to)h(complete)g(the)g Fp(aggr)n(e)n(gation)f
Ft(by)h(applying)f(the)h Fp(\002nal)g(func-)323 3402
y(tion)f Ft(\()p Fr(finalfn)p Ft(\))g(for)h(e)o(v)o(ery)g
Fp(aggr)n(e)n(gate)g(function)p Ft(.)p eop
%%Page: 66 66
66 65 bop 270 60 a Ft(66)82 b Fm(CHAPTER)14 b(3.)28 b(POSTGRESQL)13
b(FR)n(OM)f(THE)i(PR)n(OGRAMMER'S)f(POINT)f(OF)g(VIEW)345
234 y Fo(\017)25 b Ft(Store)10 b(the)i(tuple)f(containing)g(the)h(ne)o
(w)g(v)o(alues)f(\(the)h(results)f(of)h(the)f Fp(aggr)n(e)n(gate)g
(functions)p Ft(\))g(and)395 294 y(hand)h(it)g(back.)270
405 y(Note)j(that)g(the)g(procedure)f(described)i(abo)o(v)o(e)f(only)g
(returns)g(one)g(tuple)g(\(i.e.)24 b(it)15 b(processes)h(just)f(one)270
465 y(group)f(and)h(when)f(the)h(end)g(of)f(the)h(group)f(is)h
(detected)g(it)f(processes)i(the)f Fp(aggr)n(e)n(gate)f(functions)g
Ft(and)270 524 y(hands)21 b(back)f(one)h(tuple\).)39
b(T)l(o)20 b(retrie)o(v)o(e)g(all)g(tuples)h(\(i.e.)40
b(to)20 b(process)h(all)f(groups\))g(the)g(function)270
584 y Fr(execAgg\(\))15 b Ft(has)i(to)f(be)g(called)h(\(returning)d(a)i
(ne)o(w)h(tuple)e(e)o(v)o(ery)h(time\))g(until)f(it)h(returns)g(a)g
Fr(NULL)270 644 y Ft(pointer)c(indicating)f(that)h(there)g(are)h(no)f
(groups)g(left)g(to)g(process.)270 807 y Fh(3.7.2)59
b(Ho)o(w)15 b(the)g(Ha)o(ving)e(Clause)i(is)g(Implemented)270
908 y Ft(The)k(basic)g(idea)f(of)g(the)g(implementation)f(is)i(to)f
(attach)h(the)f Fp(oper)o(ator)h(tr)n(ee)g Ft(b)o(uilt)f(for)f(the)h
Fp(having)270 968 y(clause)e Ft(to)f(the)g(\002eld)g
Fr(qpqual)f Ft(of)h(node)g Fr(AGG)g Ft(\(which)g(is)h(the)f(top)g(node)
g(of)g(the)g(query)g(tree\).)23 b(No)o(w)270 1028 y(the)17
b(e)o(x)o(ecutor)g(has)h(to)f(e)o(v)o(aluate)g(the)g(ne)o(w)g
Fp(oper)o(ator)h(tr)n(ee)g Ft(attached)f(to)g Fr(qpqual)g
Ft(for)f(e)o(v)o(ery)h(group)270 1087 y(processed.)26
b(If)15 b(the)h(e)o(v)o(aluation)e(returns)h Fr(true)h
Ft(the)f(group)g(is)h(taken)f(into)g(account)h(otherwise)f(it)h(is)270
1147 y(ignored)c(and)g(the)g(ne)o(xt)h(group)e(will)h(be)h(e)o
(xamined.)270 1267 y(In)21 b(order)g(to)g(implement)g(the)g
Fp(having)g(clause)h Ft(a)f(v)o(ariety)g(of)g(changes)h(ha)o(v)o(e)g
(been)f(made)h(to)f(the)270 1326 y(follo)o(wing)11 b(stages:)345
1437 y Fo(\017)25 b Ft(The)15 b Fp(parser)h(stage)f Ft(has)h(been)f
(modi\002ed)g(slightly)g(to)g(b)o(uild)g(up)g(and)h(transform)e(an)h
Fp(oper)o(ator)395 1497 y(tr)n(ee)e Ft(for)e(the)h Fp(having)h(clause)p
Ft(.)345 1612 y Fo(\017)25 b Ft(The)12 b Fp(r)n(e)o(write)i(system)f
Ft(has)g(been)g(adapted)f(to)g(be)h(able)f(to)h(use)f
Fp(vie)o(ws)i Ft(with)e(the)g Fp(having)g(logic)p Ft(.)345
1727 y Fo(\017)25 b Ft(The)12 b Fp(planner/optimizer)g
Ft(no)o(w)g(takes)g(the)g Fp(oper)o(ator)h(tr)n(ee)g
Ft(of)f(the)g Fp(having)g(clause)g Ft(and)h(attaches)395
1787 y(it)f(to)g(the)g Fr(AGG)g Ft(node)h(\(which)e(is)i(the)f(top)h
(node)f(of)g(the)g Fp(queryplan)p Ft(\).)345 1901 y Fo(\017)25
b Ft(The)13 b Fp(e)o(xecutor)g Ft(has)g(been)g(modi\002ed)e(to)i(e)o(v)
o(aluate)f(the)h Fp(oper)o(ator)g(tr)n(ee)g Ft(\(i.e.)k(the)12
b(internal)g(repre-)395 1961 y(sentation)g(of)f(the)i
Fp(having)e(quali\002cation)p Ft(\))g(attached)h(to)g(the)h
Fr(AGG)f Ft(node)g(and)g(the)g(results)g(of)g(the)395
2021 y Fp(aggr)n(e)n(gation)f Ft(are)h(only)g(considered)g(if)g(the)g
(e)o(v)o(aluation)g(returns)g Fr(true)p Ft(.)270 2132
y(In)g(the)g(follo)o(wing)e(sections)j(we)f(will)g(describe)g(the)g
(changes)h(made)f(to)g(e)o(v)o(ery)g(single)g(stage)h(in)f(detail.)270
2285 y Fn(The)g(Parser)i(Stage)270 2386 y Ft(The)g(grammar)f(rules)g
(of)g(the)h Fp(parser)g Ft(de\002ned)g(in)f Fr(gram.y)g
Ft(did)g(not)h(require)e(an)o(y)i(changes)h(\(i.e.)k(the)270
2446 y(rules)14 b(had)g(already)g(been)g(prepared)g(for)f(the)h
Fp(having)g(clause)p Ft(\).)21 b(The)15 b Fp(oper)o(ator)f(tr)n(ee)h
Ft(b)o(uilt)f(up)g(for)f(the)270 2506 y Fp(having)f(clause)h
Ft(is)f(attached)h(to)f(the)g(\002eld)g Fr(havingClause)f
Ft(of)h(the)h Fr(SelectStmt)e Ft(node)h(handed)270 2565
y(back)h(by)f(the)g Fp(parser)p Ft(.)270 2685 y(The)18
b Fp(tr)o(ansformation)g Ft(procedures)f(applied)h(to)f(the)h(tree)f
(handed)h(back)g(by)f(the)h Fp(parser)g Ft(transform)270
2745 y(the)d Fp(oper)o(ator)g(tr)n(ee)g Ft(attached)g(to)g(the)f
(\002eld)h Fr(havingClause)e Ft(using)i(e)o(xactly)g(the)f(same)i
(functions)270 2804 y(used)j(for)f(the)h(transformation)e(of)i(the)g
Fp(oper)o(ator)g(tr)n(ee)h Ft(for)e(the)h Fp(wher)n(e)g(clause)p
Ft(.)36 b(This)20 b(is)f(possible)270 2864 y(because)c(both)e(trees)h
(are)g(b)o(uilt)g(up)f(by)h(the)g(same)h(grammar)d(rules)i(of)g(the)g
Fp(parser)g Ft(and)g(are)g(therefore)270 2924 y(compatible.)h
(Additional)9 b(checks)j(which)e(make)g(sure)h(that)f(the)h
Fp(having)f(clause)h Ft(in)n(v)o(olv)o(es)f(at)h(least)g(one)270
2984 y Fp(aggr)n(e)n(gate)f(function)g Ft(etc.)15 b(are)c(performed)e
(at)h(a)h(later)f(point)g(in)g(time)h(in)f(the)h Fp(planner/optimizer)f
Ft(stage.)270 3103 y(The)24 b(necessary)h(changes)f(ha)o(v)o(e)g(been)g
(applied)g(to)g(the)f(follo)o(wing)g(functions)g(included)g(in)h(the)
270 3163 y(\002le)19 b Fk(:)8 b(:)g(:)p Fr
(/src/backend/parser/analyze.c)o Ft(.)33 b(Note,)21 b(that)d(only)h
(the)g(rele)o(v)o(ant)f(parts)h(of)270 3223 y(the)e(af)o(fected)f(code)
g(are)h(presented)f(instead)h(of)g(the)f(whole)h(functions.)28
b(Ev)o(ery)17 b(added)g(source)f(line)270 3283 y(will)f(be)h(marked)e
(by)h(a)h Fr('+')f Ft(at)h(the)f(be)o(ginning)g(of)g(the)g(line)h(and)f
(e)o(v)o(ery)g(changed)h(source)f(line)g(will)270 3342
y(be)f(marked)f(by)h(a)g Fr('!')19 b Ft(throughout)13
b(the)h(follo)o(wing)e(code)i(listings.)21 b(Whene)o(v)o(er)13
b(a)h(part)g(of)f(the)h(code)270 3402 y(which)e(is)h(not)f(rele)o(v)o
(ant)f(at)i(the)f(moment)g(is)h(skipped,)f(three)g(v)o(ertical)h(dots)f
(are)g(inserted)g(instead.)p eop
%%Page: 67 67
67 66 bop 198 60 a Fm(3.7.)29 b(THE)13 b(REALIZA)-6 b(TION)14
b(OF)e(THE)h(HA)-7 b(VING)12 b(CLA)m(USE)622 b Ft(67)273
234 y Fo(\017)25 b Fr(transformInsertStmt\(\))323 294
y Ft(This)14 b(function)e(becomes)i(is)g(in)n(v)o(oked)e(e)o(v)o(ery)i
(time)f(a)g(SQL)h Fr(insert)f Ft(statement)g(in)n(v)o(olving)g(a)323
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%%Page: 108 108
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showpage
$F2psEnd
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@endspecial 517 3325 a(Figure)12 b(3.14:)j(Data)e(structure)e(of)h
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Ft(\))h(are)f(presented)g(including)g(parts)g(of)g(the)g(added)h
(source)f(code.)1133 3552 y(116)p eop
%%Page: 117 117
117 116 bop 198 633 a Fq(Bibliograph)n(y)198 892 y Ft([D)n(A)-6
b(TE96])99 b(C.)15 b(J.)g(Date)f(with)g(H.)g(Darwen:)k
Fp(A)d(Guide)f(to)f(the)h(SQL)g(Standar)n(d)p Ft(,)h(F)o(ourth)e
(Edition,)505 951 y(Addison-W)l(esle)o(y)g(1996)198 1051
y([ULL88])127 b(Jef)o(fre)o(y)12 b(D.)h(Ullman:)i Fp(Principles)e(of)f
(Database)h(and)f(Knowledge)g(-)g(Base)i(Systems)p Ft(,)505
1111 y(V)-6 b(olume)12 b(1,)g(Computer)g(Science)h(Press)f(1988)198
1210 y([D)n(A)-6 b(TE94])99 b(C.)23 b(J.)g(Date:)36 b
Fp(An)23 b(Intr)n(oduction)e(to)h(Database)g(Systems)p
Ft(,)k(V)-6 b(ol.)23 b(1,)i(6th)d(Edition,)505 1270 y(Addison-W)l(esle)
o(y)13 b(1994)198 1370 y([LOCK98])88 b(Thomas)23 b(Lockhart:)36
b Fp(P)l(ostgr)n(eSQL)23 b(Pr)n(ogr)o(ammer')n(s)h(Guide)p
Ft(,)h(part)d(of)g(the)h(Post-)505 1430 y(greSQL)12 b(documentation.)
198 1529 y([ST)o(ON89])94 b(Michael)16 b(Stonebraker)d(et.)j(al.:)21
b Fp(On)16 b(Rules,)h(Pr)n(ocedur)n(es,)h(Cac)o(hing)d(and)g(V)l(ie)o
(ws)i(in)505 1589 y(Data)12 b(Base)i(Systems)p Ft(.)1061
3552 y(117)p eop
%%Trailer
end
userdict /end-hook known{end-hook}if
%%EOF