使用join进行更新需要很长时间

Question

我在更新表时遇到问题.我正在运行以下查询:

UPDATE Table1 SEt entrena = c.Count 
FROM Table1 AS p INNER JOIN (
SELECT e.EmplID, COUNT(e.EmplID ) as Count 
FROM Table2 AS e WHERE e.Start >= @Start AND e.Start <=@End 
GROUP BY e.EmplID ) AS c ON p.EmplID = c.EmplID
WHERE P.Date  = '2050-12-31'

Table1有12000行,连接中的select只有51行,但更新大约需要2分钟,但是如果我删除where clase p.date = '2050-12-31',则更新只需不到一秒钟.我无法弄清楚如何解决它.我正在使用SQL Server 2008.

两个表都没有索引.

Answer 1

这是您的查询:

UPDATE Table1
    SET entrena = c.Count 
    FROM Table1 p INNER JOIN
         (SELECT e.EmplID, COUNT(e.EmplID ) as Count 
          FROM Table2 e
          WHERE e.Start >= @Start AND e.Start <=@End 
          GROUP BY e.EmplID
         ) c
    ON p.EmplID = c.EmplID
    WHERE P.Date  = '2050-12-31';

首先,您需要将第一行更改为:

UPDATE p

当您在from子句中定义别名时,您需要update在正确的事情中使用它.(我希望您的查询在SQL Server中生成错误,但它不会.)

要优化此查询,您需要添加索引.我会建议这两个:

Table1(date, EmplID)
Table2(EmplId, Start)

然后,您可能会发现相关子查询版本更快,特别是如果该where子句具有高选择性:

UPDATE p
    SET entrena = (SELECT COUNT(e.EmplID ) as Count 
                   FROM Table2 e
                   WHERE e.Start >= @Start AND e.Start <=@End AND
                         p.EmplID = e.EmplID
                  )
    FROM Table1 p
    WHERE P.Date  = '2050-12-31';

但是,我怀疑p对比table1是你的性能问题的根源.