mysql - IF 内的子查询作为具有空值的列的值

Question

给定:

t1{id,type}
t2{type,table1_id}

我正在使用这个:

SELECT IF(t1.type IS NULL, 'some default', t1.type) as ret from t1

我想做这样的事情:

SELECT IF(
    t1.type IS NULL, 
    IF(
        (SELECT t2.type FROM t2 WHERE t2.table1_id=t1.id LIMIT 1) IS NOT NULL,
        table2.type,
        'some defaults'
    ),
    t1.type
) as ret from table1

Answer 1

这个——

SELECT IF(
    t1.type IS NULL, 
    IF(
        (SELECT t2.type FROM t2 
           WHERE t2.table1_id=t1.id LIMIT 1)
           IS NOT NULL,
        t2.type,
        'some defaults'),
    t1.type
) as ret from t1, t2 where t1.id = t2.table1_id

好像work .