Doc: improve user docs and code comments about EXISTS(SELECT * ...). Point out that Postgres automatically optimizes away the target list of an EXISTS' subquery, except in weird cases such as target lists containing set-returning functions. Thus, both common conventions EXISTS(SELECT * FROM ...) and EXISTS(SELECT 1 FROM ...) are overhead-free and there's little reason to prefer one over the other.
In the code comments, mention that the SQL spec says that EXISTS(SELECT * FROM ...) should be interpreted as EXISTS(SELECT some-literal FROM ...), but we don't choose to do it exactly that way. Author: Peter Eisentraut <[email protected]> Reviewed-by: Tom Lane <[email protected]> Discussion: https://postgr.es/m/[email protected] Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/65a3ff8f1be0186a9c207821bcf0f543545a04d9 Modified Files -------------- doc/src/sgml/func/func-subquery.sgml | 10 ++++++++-- src/backend/optimizer/plan/subselect.c | 8 +++++++- 2 files changed, 15 insertions(+), 3 deletions(-)
