mysql查询，从3个表中进行选择

Question

我与查询拉动3个表中的唯一值进行争吵。这是更好地完成在2个单独的查询？

查询是：

count as returned (
all leadID from lds where status = "ok" 
AND leadID is also in rlds with recID="999" 
AND rdate > (03-20-2012) 
+ 
(all distinct leadID from plds where recID="999" 
AND change != NULL 
AND pdate > (03-20-2012)) 

工作查询的结果应该是 “2”：leadID 1和leadID 4

表LDS：

leadID |状态
1 |好吧
2 |不好
3 |好吧

表plds：
leadID | recID |改变| pdate
4 | 999 | ch1 | 03-27-2012
4 | 999 | ch2 | 03-27-2012
5 | 888 | NULL | 03-27-2012

表格地址：
leadID | recID2 | rdate
1 | 999 | 03-27-2012
6 | 999 | 03-27-2012

谢谢！

Answer 1

SELECT Ids.leadId 
FROM 
    Ids JOIN 
    rlds ON rlds.leadId = Ids.LeadId AND recID = 999 AND rdate > '03-20-2012' 
WHERE Ids.Status = 'ok' 

UNION 

SELECT leadId 
FROM pIds 
WHERE recID = 999 AND change IS NOT NULL AND pdate > '03-20-2012' 

Answer 2

您可以使用UNION关键字中检索一个阵列中的2行，第一个包含您的第一场比赛的数量和你的第二个比赛的Seconde系列计数。

然后，您可以使用SUM关键字将封闭选择中的两行完全相加。结果将是一个单一的行计数你的数量。

SELECT sum(1) 
FROM 
(
SELECT count(1) 
FROM lds 
INNER JOIN rlds ON lds.leadid = plds.leadid 
WHERE lds.status='ok' AND rlds.recid2=999 AND rlds.pdate > '03-20-2012' 

UNION 

SELECT count(1) 
FROM plds 
WHERE plds.recid=999 
AND change != NULL 
AND pdate > '03-20-2012' 
) AS tmpcount