PostgreSQL 更新 + 加入一个额外的 WHERE 子句

Question

I need to use JOIN in my UPDATE so that I would only fill the value of the column where the condition applies.

I was trying to do this, but I receive an error saying "syntax error at or near 'LEFT'":

UPDATE products_mpn SET scrap = 5
LEFT JOIN products ON products.id = products_mpn.product
WHERE products.category_id = 101 OR products.category_id = 104

I have found that I could join the tables this way:

UPDATE t1
SET t1.c1 = new_value
FROM t2
WHERE t1.c2 = t2.c2;

But the issue is that I can not use my specific WHERE clause then. Any ideas on how to achieve this?

Answer 1

Try this:

UPDATE products_mpn SET scrap = 5 WHERE product = ( SELECT product FROM products_mpn
LEFT JOIN products ON products.id = products_mpn.product
WHERE products.category_id = 101 OR products.category_id = 104)

Answer 2

UPDATE products_mpn SET scrap = 5 WHERE product IN ( SELECT id FROM products WHERE category_id IN (101,104))