[英]How can I check sub query returns nothing?
這是我的查詢:
SELECT
CASE WHEN if_this_matches_nothing(SELECT 1 FROM mytable WHERE id = :id) THEN 0
ELSE 1 END
MySQL中有這樣的if_this_matches_nothing
函數嗎?
您正在尋找NOT EXISTS
:
SELECT (CASE WHEN NOT EXISTS (SELECT 1 FROM mytable WHERE id = :id)
THEN 0 ELSE 1
END) as flag
你實際上可以縮短它。 MySQL中不需要CASE
:
SELECT (NOT EXISTS (SELECT 1 FROM mytable WHERE id = :id) ) as flag
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