作者world294 (TRJ.Win32)
看板Database
标题[SQL ] MySQL UNION 资源重复使用问题
时间Tue Mar 30 15:00:57 2010
Hi,有个 MySQL 问题想请教大家
SQL 语法如下：
SELECT cid, uid FROM test WHERE status <> 0
UNION SELECT t2.cid t1.uid FROM test t1 JOIN test t2 ON (t1.cid = t2.uid)
WHERE a2.status NOT IN (0, 1)
UNION SELECT t3.cid t2.uid FROM test t1 JOIN test t2 ON (t1.cid = t2.uid)
JOIN test t3 ON (t2.cid = t3.uid)
WHERE a2.status NOT IN (0, 1) AND a3.status NOT IN (0, 1, 2)
...do 7!
问题在於
下一个交集结果的条件依赖着上一次交集的结果，却还要重复 JOIN
ex :
一次
SELECT t2.cid t1.uid FROM test t1 JOIN test t2 ON (t1.cid = t2.uid)
二次
SELECT t2.cid t1.uid FROM test t1 JOIN test t2 ON (t1.cid = t2.uid)
JOIN test t3 ....
n 次
SELECT t2.cid t1.uid FROM test t1 JOIN test t2 ON (t1.cid = t2.uid)
JOIN test t3 ....JOIN test n!
要怎麽把上次的结果拿来下次使用，不用再重复 query & join
thx
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