Mark null-returning RTEs in outer joins as nullable #1
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RTEs that appear in the right side of a left join are marked as 'nullable'.
The column references to a nullable RTE within the join's RTE are also
marked as 'nullable'. This concept is introduced in Postgresql v16.
The change in Postgresql v16's pullup_replace_vars_callback() function causes
different plans to be generated depending on whether appropriate RTEs are
marked nullable. Without marking nullable, in a left join, any function call
expression containing right RTE's columns as arguments are not evaluated at
the scan level, rather it is evaluated after the join is performed. At that
point, the function call may receive null input, which was unexpected in
previous Postgresql versions.
See:
----
- Postgresql v16's commit: Make Vars be outer-join-aware
https://www.postgresql.org/message-id/830269.1656693747@sss.pgh.pa.us
- The 'Vars and PlaceHolderVars' section in the Postgresql v16's
optimizer/README.md
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jrgemignani
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RTEs that appear in the right side of a left join are marked as 'nullable'. The column references to a nullable RTE within the join's RTE are also marked as 'nullable'. This concept is introduced in Postgresql v16.
The change in Postgresql v16's pullup_replace_vars_callback() function causes different plans to be generated depending on whether appropriate RTEs are marked nullable. Without marking nullable, in a left join, any function call expression containing right RTE's columns as arguments are not evaluated at the scan level, rather it is evaluated after the join is performed. At that point, the function call may receive null input, which was unexpected in previous Postgresql versions.
See:
Postgresql v16's commit: Make Vars be outer-join-aware https://www.postgresql.org/message-id/830269.1656693747@sss.pgh.pa.us
The 'Vars and PlaceHolderVars' section in the Postgresql v16's optimizer/README.md