Question

SELECT * 
FROM   sec 
WHERE  sec.cu IN (SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  EXISTS (SELECT * 
                                 FROM   hact h WITH ( nolock), 
                                 JOIN   dport p WITH ( nolock) ON h.ic = p.ic
                                 WHERE  s.cu = h.cu )

                  UNION 
                  SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  EXISTS(SELECT * 
                                FROM   schanges c WITH ( nolock) 
                                WHERE  s.cu = c.cu) 
                  UNION 
                  SELECT s.cu 
                  FROM   sec s WITH (nolock) 
                  WHERE  s.cu IN (SELECT DISTINCT cu 
                                  FROM   suk WITH (nolock))) 
       AND EXISTS (SELECT * 
                   FROM   hact h WITH (nolock) 
                          JOIN port p WITH (nolock) 
                            ON h.ic = p.ic 
                   WHERE  sec.cu = h.cu 
                          AND p.ptype = 'X')

嗨，我有这个问题，我正在尝试优化。我试图将其转换为删除联合和转换为更可读但失败。我试图提高效率，可能只使用EXISTS而不是EXISTS。

Answer 1

这是一个应该在功能上等同的简化版本：

SELECT s.*
FROM   sec s WITH (nolock) 
WHERE (
  EXISTS (
    SELECT * 
    FROM   hact h WITH ( nolock)
    JOIN   dport p WITH ( nolock) 
      ON h.ic = p.ic
    WHERE  s.cu = h.cu 
  ) OR EXISTS (
    SELECT * 
    FROM   schanges c WITH ( nolock)
    WHERE  s.cu = c.cu
  ) OR EXISTS (
    SELECT *
    FROM   suk WITH (nolock)
    WHERE  s.cu = suk.cu
  )
) AND EXISTS (
  SELECT * 
  FROM   hact h WITH (nolock) 
  JOIN port p WITH (nolock) 
    ON h.ic = p.ic 
  WHERE  
    s.cu = h.cu 
    AND p.ptype = 'X'
)

Answer 2

我认为你可以用这种方式重写你的嵌套in / exists：

SELECT * 
FROM sec 
WHERE sec.cu IN (
  SELECT s.cu 
  FROM sec s 
  INNER JOIN hact h ON s.cu = h.cu, 
  INNER JOIN dport p ON h.ic = p.ic

  UNION ALL

  SELECT s.cu
  FROM sec s
  INNER JOIN schanges c ON s.cu = c.cu) 

  UNION ALL

  SELECT s.cu 
  FROM sec s 
  INNER JOIN suk k ON k.cu = s.cu
  INNER JOIN hact h ON s.cu = h.cu
  INNER JOIN port p ON h.ic = p.ic AND p.ptype = 'X'
)

甚至完全从子查询中删除sec表：

SELECT * 
FROM sec 
WHERE sec.cu IN (
  SELECT h.cu 
  FROM hact h
  INNER JOIN dport p ON h.ic = p.ic

  UNION ALL

  SELECT cu
  FROM schanges

  UNION ALL

  SELECT k.cu 
  FROM suk k
  INNER JOIN hact h ON s.cu = h.cu
  INNER JOIN port p ON h.ic = p.ic AND p.ptype = 'X'
)

Answer 3

只需将您的UNION子句更改为UNION ALL即可。仅此一点应该有所帮助。

为了能够在没有我们盲目猜测的情况下为您提供帮助，您将不得不向我们提供表格，密钥和索引定义以及查询计划。

Answer 4

未经测试，但我认为您可以使用连接

来执行此操作

select distinct s.*
from   sec s with (nolock)
join   hatch h1 with (nolock)
  on   h1.cu = s.cu
       join  port p1 WITH (nolock) 
         ON  h1.ic = p1.ic
        AND  p1.ptype = 'X'
left join hact h2 WITH ( nolock)
  on   h2.cu = s.cu
       join  port p2 WITH (nolock) 
         ON  h2.ic = p2.ic
left join  schanges c WITH ( nolock) 
  on   s.cu = c.cu 
left join  suc WITH ( nolock) 
  on   s.cu = suc.cu 
where h2.cu  is not null
   or c.cu   is not null
   or suc.cu is not null

union intersect可能会更快取决于查询优化器的智能程度

(   
    select s.*
    from   sec s with (nolock)
    join hact h2 WITH (nolock)
      on   h2.cu = s.cu
           join  port p2 WITH (nolock) 
             ON  h2.ic = p2.ic
  union
    select s.*
    from   sec s with (nolock)
    join  schanges c WITH ( nolock) 
      on   s.cu = c.cu 
  union
    select s.*
    from   sec s with (nolock)
    left join  suc WITH ( nolock) 
      on   s.cu = suc.cu
)
  intersect
    select s.*
    from   sec s with (nolock)
    join   hatch h1 with (nolock)
      on   h1.cu = s.cu
           join  port p1 WITH (nolock) 
             ON  h1.ic = p1.ic
            AND  p1.ptype = 'X'

我已经看到优化器在这些二级连接上变得愚蠢如果是这样，试试

select s.*
from   sec s with (nolock)
join hact h1 WITH (nolock)
  on h1.cu = s.cu
  where h1.ic in (select ic from where ptype = 'X')

请参阅我对死锁的评论和（nolock）我不考虑（nolock）一个kludge并使用它很多。
如果你看到很多死锁，那么你需要看一下。

索引cu，ic和ptype。
然后测试不同版本的查询并查看执行计划这是查询优化器可能遇到问题的查询类型查询优化器基于统计信息，甚至可以更改执行计划您可能需要包含联接的表提示。

Answer 5

我在想:(未经测试，希望保持功能等同性）

SELECT DISTINCT s.*
FROM   sec s
JOIN hact h WITH (nolock)
  ON s.cu = h.cu
LEFT JOIN dport p WITH (nolock)
  ON h.ic = p.ic
LEFT JOIN schanges c WITH (nolock)
  ON s.cu = c.cu
LEFT JOIN suk WITH (nolock)
  ON suk.cu = s.cu
JOIN port p2 WITH (nolock)
  ON h.ic = p2.ic 
WHERE p2.ptype = 'X' AND
  (p.ic IS NOT NULL OR c.cu IS NOT NULL OR suk.cu IS NOT NULL)

修改：添加了DISTINCT

将IN和UNION转换为更高效的东西（可能是EXISTS）

5 个答案: