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explain.c

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    • Tom Lane's avatar
      784e762e
      Support multi-argument UNNEST(), and TABLE() syntax for multiple functions. · 784e762e
      Tom Lane authored
      This patch adds the ability to write TABLE( function1(), function2(), ...)
      as a single FROM-clause entry.  The result is the concatenation of the
      first row from each function, followed by the second row from each
      function, etc; with NULLs inserted if any function produces fewer rows than
      others.  This is believed to be a much more useful behavior than what
      Postgres currently does with multiple SRFs in a SELECT list.
      
      This syntax also provides a reasonable way to combine use of column
      definition lists with WITH ORDINALITY: put the column definition list
      inside TABLE(), where it's clear that it doesn't control the ordinality
      column as well.
      
      Also implement SQL-compliant multiple-argument UNNEST(), by turning
      UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)).
      
      The SQL standard specifies TABLE() with only a single function, not
      multiple functions, and it seems to require an implicit UNNEST() which is
      not what this patch does.  There may be something wrong with that reading
      of the spec, though, because if it's right then the spec's TABLE() is just
      a pointless alternative spelling of UNNEST().  After further review of
      that, we might choose to adopt a different syntax for what this patch does,
      but in any case this functionality seems clearly worthwhile.
      
      Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and
      significantly revised by me
      784e762e
      History
      Support multi-argument UNNEST(), and TABLE() syntax for multiple functions.
      Tom Lane authored
      This patch adds the ability to write TABLE( function1(), function2(), ...)
      as a single FROM-clause entry.  The result is the concatenation of the
      first row from each function, followed by the second row from each
      function, etc; with NULLs inserted if any function produces fewer rows than
      others.  This is believed to be a much more useful behavior than what
      Postgres currently does with multiple SRFs in a SELECT list.
      
      This syntax also provides a reasonable way to combine use of column
      definition lists with WITH ORDINALITY: put the column definition list
      inside TABLE(), where it's clear that it doesn't control the ordinality
      column as well.
      
      Also implement SQL-compliant multiple-argument UNNEST(), by turning
      UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)).
      
      The SQL standard specifies TABLE() with only a single function, not
      multiple functions, and it seems to require an implicit UNNEST() which is
      not what this patch does.  There may be something wrong with that reading
      of the spec, though, because if it's right then the spec's TABLE() is just
      a pointless alternative spelling of UNNEST().  After further review of
      that, we might choose to adopt a different syntax for what this patch does,
      but in any case this functionality seems clearly worthwhile.
      
      Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and
      significantly revised by me