Question

我需要知道，这是正确的方法：

(SELECT id, name, 1 AS reference FROM antenna WHERE id IN (SELECT antenna_id FROM reference)) 
UNION DISTINCT
(SELECT id, name, 0 AS reference FROM antenna WHERE id NOT IN (SELECT antenna_id FROM reference))

已经做了一段时间，即使它完美无缺，也很难看。

Answer 1

脱离我的头脑，我不确定它是否有效，测试和基准：

SELECT antenna.id, antenna.name, CASE WHEN COALESCE(reference.antenna_id, 0)!=0 
THEN 1 ELSE 0 END AS reference FROM antenna LEFT JOIN reference 
ON antenna.id=reference.antenna_id

Answer 2

是。它会工作。但与JOIN相比，IN子句的性能较差。此外，IN子句限制为1000条记录。

请改用此查询 -

(SELECT id, name, 1 AS reference FROM antenna a, reference ref
where a.id = ref.antenna_id)
UNION
(SELECT id, name, 0 AS reference FROM antenna a, reference ref
where a.id != ref.antenna_id)

简化MySQL查询联合

2 个答案: