[Solved] Why does this query cause an error?SELECT a.id, b.val FROM a JOIN LATERAL (SELECT val FROM b WHERE b.a_id = a.id) ON true; | PostgreSQL

PostgreSQL - Joins in PostgreSQL

Why does this query cause an error?

SELECT a.id, b.val FROM a JOIN LATERAL (SELECT val FROM b WHERE b.a_id = a.id) ON true;

ACorrelated subquery cannot reference outer table

BMissing alias for the LATERAL subquery

CTable b is not defined in FROM clause

DUsing ON true without alias is invalid

Step-by-Step Solution

Solution:

Step 1: Check LATERAL subquery aliasing
The subquery after LATERAL must have an alias to be valid.
Step 2: Confirm error cause
Query lacks alias after subquery, causing syntax error despite ON true.
Final Answer:
Missing alias for the LATERAL subquery -> Option B
Quick Check:
LATERAL subquery must have alias even with ON true [OK]

Quick Trick: Alias every LATERAL subquery to avoid syntax errors [OK]

Common Mistakes:

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Why does this query cause an error?