tree 3638432131938203b72b2684bae84a231179c779
parent ddb4200f8f52b02afb1b866abb0785218e2c5994
author Julian Hyde <jhyde@apache.org> 1635880394 -0700
committer Julian Hyde <jhyde@apache.org> 1685247452 -0700

[CALCITE-4334] LITERAL_AGG, an internal aggregate function that returns a constant value

LITERAL_AGG is internal, so you cannot use it from SQL. A
call to LITERAL_AGG(true) is created implicitly when you
write

  SELECT deptno, SUM(sal), true
  FROM Emp
  GROUP BY deptno

Add RelBuilder.literalAgg.

RelBuilder.aggregate now adds an aggregate function to ensure
that there is at least one field. The aggregate function is
LITERAL_AGG; thus the pseudo-query

  SELECT /* no fields */
  FROM t
  GROUP BY ()

becomes the valid query

  SELECT TRUE AS dummy
  FROM t
  GROUP BY ().

Solves that problem that an Aggregate query that uses no
columns throws AssertionError in RelFieldTrimmer.trimFields.

Add an option RelBuilder.Config.preventEmptyFieldList to
turn off the behavior we just added.

Close apache/calcite#3209