postgres=# SELECT version(); version ------------------------------------------------------------ PostgreSQL 16.4, compiled by Visual C++ build 1940, 64-bit (1 row)
postgres=# DO $$ postgres$# BEGIN postgres$# IF postgres$# CASE postgres$# WHEN TRUE postgres$# THEN TRUE postgres$# END postgres$# THEN postgres$# NULL; postgres$# END IF; postgres$# END postgres$# $$; ERROR: syntax error at end of input LINE 5: WHEN TRUE ^
It seems error here because first THEN bound to IF statement rather than CASE expression. Workaround here would be using parenthesis:
postgres=# DO $$ postgres$# BEGIN postgres$# IF postgres$# (CASE postgres$# WHEN TRUE postgres$# THEN TRUE postgres$# END) postgres$# THEN postgres$# NULL; postgres$# END IF; postgres$# END postgres$# $$; DO
If behavior can not be changed for compatibility reasons, it at least can use better error message.
It is an interesting use case, but I am afraid it can be fixed (enhanced) without a strong rewrite of the plpgsql engine.
plpgsql parser knows nothing about embedded SQL expressions. It just tries to cut the string between IF and THEN, and in this case, it should be confused.
This is a feature - it is the cost of a very simple plpgsql parser, that doesn't support expressions explicitly.
