postgres 在子句中选择查询

Question

Postgres is not able to compile the query (not able to identify if a column exists on the table in subquery) within in clause, I am citing a sample query

select * from table_a where (id is null or id not in (select distinct id from table_b)) 

This query was running fine in production, but a data defect was found and realized that there is no column id in table_b at all, even then the query was running without any compilation issues

Is this a known defect or did any one encounter this issue?

Answer 1

From the postgresql documentation : EXISTS (subquery) -> The subquery can refer to variables from the surrounding query, which will act as constants during any one evaluation of the subquery.

The column id in the subquery is referring to table_a, not to table_b (table_b does not have a column named id).

All this queries are equivalent:

SELECT * 
FROM table_a
WHERE table_a.id IN (SELECT table_a.id)

SELECT * 
FROM table_a
WHERE table_a.id IN (SELECT id)

SELECT * 
FROM table_a
WHERE table_a.id IN (SELECT id FROM table_b)

SELECT * 
FROM table_a
WHERE table_a.id IN (SELECT table_a.id FROM table_b)

This query failed (column table_b.id does not exist):

SELECT * 
FROM table_a
WHERE table_a.id NOT IN (SELECT table_b.id FROM table_b)