Question

我使用以下查询根据指定的条件更新一列。我正在使用“内部联接”，但即使它不必更新任何记录（0条记录），运行查询也需要15秒以上。

UPDATE CONFIGURATION_LIST
SET DUPLICATE_SERIAL_NUM = 0
FROM CONFIGURATION_LIST
INNER JOIN (SELECT DISTINCT APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER, COUNT(*) AS NB
            FROM CONFIGURATION_LIST
            WHERE
                PLANT = '0067'
                AND APPLIED_SERIAL_NUMBER IS NOT NULL 
                AND APPLIED_SERIAL_NUMBER !=''
                AND DUPLICATE_SERIAL_NUM = 1
            GROUP BY 
                APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER
            HAVING
                COUNT(*) = 1) T2 ON T2.APPLIED_SERIAL_NUMBER = CONFIGURATION_LIST.APPLIED_SERIAL_NUMBER
                                 AND T2.APPLIED_MAT_CODE = CONFIGURATION_LIST.APPLIED_MAT_CODE
WHERE 
    CONFIGURATION_LIST.PLANT = '0067'
    AND DUPLICATE_SERIAL_NUM = 1

索引与APPLIED_SERIAL_NUMBER和APPLIED_MAT_CODE一致，碎片也很好。

请您帮我解决上述查询效果。

Answer 1

首先，在使用DISTINCT时，您不需要GROUP BY。 SQL Server可能会忽略它，但无论如何这都是一个坏主意：

UPDATE CONFIGURATION_LIST
SET DUPLICATE_SERIAL_NUM = 0
    FROM CONFIGURATION_LIST INNER JOIN
         (SELECT APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER, COUNT(*) AS NB
          FROM CONFIGURATION_LIST cl
          WHERE cl.PLANT = '0067' AND
                cl.APPLIED_SERIAL_NUMBER IS NOT NULL AND
                cl.APPLIED_SERIAL_NUMBER <> ''
                cl.DUPLICATE_SERIAL_NUM = 1
          GROUP BY cl.APPLIED_MAT_CODE, cl.APPLIED_SERIAL_NUMBER
          HAVING COUNT(*) = 1
         ) T2
         ON T2.APPLIED_SERIAL_NUMBER = CONFIGURATION_LIST.APPLIED_SERIAL_NUMBER AND
            T2.APPLIED_MAT_CODE = CONFIGURATION_LIST.APPLIED_MAT_CODE
WHERE CONFIGURATION_LIST.PLANT = '0067' AND
      DUPLICATE_SERIAL_NUM = 1;

对于此查询，您需要以下索引：CONFIGURATION_LIST(PLANT, DUPLICATE_SERIAL_NUM, APPLIED_SERIAL_NUMBER, APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER)。

HAVING COUNT(*) = 1表示您可能真的想要NOT EXISTS（通常会更快）。但是你没有真正解释查询应该做什么，你只是说这段代码很慢。

Answer 2

看起来您正在检查表中存在于同一个表中的具有相同值的行，如果没有，则将重复列更新为零。如果您的表具有唯一键（标识字段或复合键），您可以执行以下操作：

UPDATE C
SET C.DUPLICATE_SERIAL_NUM = 0
FROM 
  CONFIGURATION_LIST C
where 
  not exists (
    select
      1 
    FROM
      CONFIGURATION_LIST C2
    where
      C2.APPLIED_SERIAL_NUMBER = C.APPLIED_SERIAL_NUMBER and
      C2.APPLIED_MAT_CODE = C.APPLIED_MAT_CODE and
      C2.UNIQUE_KEY_HERE != C.UNIQUE_KEY_HERE
  ) and 
  C.PLANT = '0067' and
  C.DUPLICATE_SERIAL_NUM = 1

Answer 3

我会首先尝试选择：

select APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER, count(*) as n
from CONFIGURATION_LIST cl
where
    cl.PLANT='0067' and
    cl.APPLIED_SERIAL_NUMBER IS NOT NULL and
    cl.APPLIED_SERIAL_NUMBER <> ''
group by APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER;

您获得了多少行以及需要多长时间？

如果从表中删除DUPLICATE_SERIAL_NUM列，则可能非常简单。 DUPLICATE_SERIAL_NUM表示您正在搜索重复项。在计算行数时，可以引入一个包含计数的简单表：

create table CLCOUNT ( N int unsigned, C int /* or what APPLIED_MAT_CODE is */, S int /* or what APPLIED_SERIAL_NUMBER is */, PLANT char(20) /* or what PLANT is */, index unique (C,S,PLANT), index(PLANT,N));
insert into CLCOUNT select count(*), cl.APPLIED_MAT_CODE, cl.APPLIED_SERIAL_NUMBER, cl.PLANT
from CONFIGURATION_LIST cl
where
    cl.PLANT='0067' and
    cl.APPLIED_SERIAL_NUMBER IS NOT NULL and
    cl.APPLIED_SERIAL_NUMBER <> ''
group by APPLIED_MAT_CODE, APPLIED_SERIAL_NUMBER;

这需要多长时间？

现在您可以简单地select * from CLCOUNT where PLANT='0067' and N=1;

这远非完美。但是你应该能够分析（EXPLAIN SELECT ...）你的查询并找出它需要这么长时间的原因。

使用内部联接更新查询的速度很慢

3 个答案: