diff --git a/doc/src/sgml/array.sgml b/doc/src/sgml/array.sgml index bbc0a07f5601b0758c0e80bf124953007dc344d6..aa7ecdc7113ad57cb63401716248c6a1278c7645 100644 --- a/doc/src/sgml/array.sgml +++ b/doc/src/sgml/array.sgml @@ -10,14 +10,13 @@ This must become a chapter on array behavior. Volunteers? - thomas 1998-01-12 </Para> <Para> - <ProductName>Postgres</ProductName> allows attributes of an instance to be defined - as fixed-length or variable-length multi-dimensional - arrays. Arrays of any base type or user-defined type - can be created. To illustrate their use, we first create a - class with arrays of base types. + <ProductName>Postgres</ProductName> allows attributes of a class + to be defined as variable-length multi-dimensional + arrays. Arrays of any built-in type or user-defined type + can be created. To illustrate their use, we create this class: <ProgramListing> -CREATE TABLE SAL_EMP ( +CREATE TABLE sal_emp ( name text, pay_by_quarter int4[], schedule text[][] @@ -26,10 +25,10 @@ CREATE TABLE SAL_EMP ( </Para> <Para> - The above query will create a class named SAL_EMP with + The above query will create a class named <FirstTerm>sal_emp</FirstTerm> with a <FirstTerm>text</FirstTerm> string (name), a one-dimensional array of <FirstTerm>int4</FirstTerm> (pay_by_quarter), which represents the employee's - salary by quarter and a two-dimensional array of <FirstTerm>text</FirstTerm> + salary by quarter, and a two-dimensional array of <FirstTerm>text</FirstTerm> (schedule), which represents the employee's weekly schedule. Now we do some <FirstTerm>INSERTS</FirstTerm>s; note that when appending to an array, we enclose the values within @@ -37,20 +36,18 @@ CREATE TABLE SAL_EMP ( this is not unlike the syntax for initializing structures. <ProgramListing> -INSERT INTO SAL_EMP +INSERT INTO sal_emp VALUES ('Bill', '{10000, 10000, 10000, 10000}', '{{"meeting", "lunch"}, {}}'); -INSERT INTO SAL_EMP +INSERT INTO sal_emp VALUES ('Carol', '{20000, 25000, 25000, 25000}', '{{"talk", "consult"}, {"meeting"}}'); </ProgramListing> - By default, <ProductName>Postgres</ProductName> uses the "one-based" numbering - convention for arrays -- that is, an array of n elements starts with array[1] and ends with array[n]. - Now, we can run some queries on SAL_EMP. First, we + Now, we can run some queries on sal_emp. First, we show how to access a single element of an array at a time. This query retrieves the names of the employees whose pay changed in the second quarter: @@ -63,6 +60,10 @@ SELECT name FROM sal_emp WHERE pay_by_quarter[1] <> pay_by_quarter[2]; Carol (1 row) </ProgramListing> + + <ProductName>Postgres</ProductName> uses the "one-based" numbering + convention for arrays --- that is, an array of n elements starts with + array[1] and ends with array[n]. </Para> <Para> @@ -82,8 +83,10 @@ SELECT pay_by_quarter[3] FROM sal_emp; <Para> We can also access arbitrary slices of an array, or - subarrays. This query retrieves the first item on - Bill's schedule for the first two days of the week. + subarrays. An array slice is denoted by writing + "lower subscript : upper subscript" for one or more array + dimensions. This query retrieves the first item on + Bill's schedule for the first two days of the week: <ProgramListing> SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill'; @@ -93,6 +96,59 @@ SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill'; {{"meeting"},{""}} (1 row) </ProgramListing> + + We could also have written + +<ProgramListing> +SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill'; +</ProgramListing> + + with the same result. +</Para> + +<Para> + An array value can be replaced completely: + +<ProgramListing> +UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}' + WHERE name = 'Carol'; +</ProgramListing> + + or updated at a single entry: + +<ProgramListing> +UPDATE sal_emp SET pay_by_quarter[4] = 15000 + WHERE name = 'Bill'; +</ProgramListing> + + or updated in a slice: + +<ProgramListing> +UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}' + WHERE name = 'Carol'; +</ProgramListing> +</Para> + +<Para> + It is not currently possible to resize an array value except by + complete replacement; for example, we couldn't change a four- + element array value to a five-element value with a single + assignment to array[5]. +</Para> + +<Para> + The syntax for CREATE TABLE allows fixed-length arrays to be + defined: + +<ProgramListing> +CREATE TABLE tictactoe ( + squares int4[3][3] +); +</ProgramListing> + + However, the current implementation does not enforce the array + size limits --- the behavior is the same as for arrays of + unspecified length. </Para> </Chapter>