mysql查询需要很长时间才能执行

Question

这是我的查询需要3秒才能执行：

SELECT I.itemname,
   I.overdue,
   D.value,
   I.itemid,
   icd.ecwstatus  AS status,
   C.inactiveflag AS inactive,
   icd.validfrom,
   icd.validto
FROM   items I
   JOIN itemdetail D
     ON I.itemtype = 'I'
        AND I.itemid = D.itemid
        AND D.propid = 13
   LEFT OUTER JOIN icd
                ON icd.code = D.value
   LEFT OUTER JOIN edi_icdcodes C
                ON I.itemid = C.itemid
WHERE  I.deleteflag = 0
   AND ( icd.validfrom <= '2012-12-06'
          OR icd.validfrom IS NULL )
   AND ( icd.validto >= '2012-12-06'
          OR icd.validto IS NULL )
   AND I.itemname LIKE 'A%'
   AND ( I.keyname = 'Assessments' )
ORDER  BY I.itemname ASC limit 0,6;  

我在项目表中的多列itemType，deleteFlag，keyName，itemName上具有索引IX_items_itemType_deleteFlag_keyName_itemName，并且在join和where子句中使用的其他表列上也具有索引。

那么如何提高查询性能呢？

谢谢

Answer 1

您在那里执行的操作是使用基本表，然后执行一些“联接”，然后才执行“ where”请求。 为了快速起见，请尝试将您的情况包括在“加入”中。 在这种方式中，它选择“加入”请求中的不同行，而不是之后。

SELECT I.itemname,
   I.overdue,
   D.value,
   I.itemid,
   icd.ecwstatus  AS status,
   C.inactiveflag AS inactive,
   icd.validfrom,
   icd.validto
FROM   items I
JOIN itemdetail D
  ON I.itemtype = 'I'
    AND I.itemid = D.itemid
    AND D.propid = 13
    AND I.deleteflag = 0
LEFT OUTER JOIN icd
            ON icd.code = D.value
            AND ( icd.validfrom <= '2012-12-06'
                  OR icd.validfrom IS NULL )
            AND ( icd.validto >= '2012-12-06'
                  OR icd.validto IS NULL )
LEFT OUTER JOIN edi_icdcodes C
            ON I.itemid = C.itemid
            AND I.itemname LIKE 'A%'
            AND ( I.keyname = 'Assessments' )
ORDER  BY I.itemname ASC limit 0,6;  

Answer 2

我将根据用于where子句和order by的多个键列在您的项目表上建立索引。 我将索引设置为最小的结果放在前面。 例如，您专门在寻找“评估”。 如果您的表有1百万条记录，其中600k属于项目类型“ I”，但只有5k是“ Assessments”，那么最前面的最小部分对于您的查询TO流程可能更好。

我要你：

items table indexed on ( keyname, itemtype, deleteflag, itemname )
ItemDetail table, indexed ON ( itemid, propid )
icd table indexed ON ( code, validfrom, validto, ecwstatus )
edi_icdcodes table index ON (itemid)


SELECT 
      I.itemname,
      I.overdue,
      D.value,
      I.itemid,
      icd.ecwstatus  AS status,
      C.inactiveflag AS inactive,
      icd.validfrom,
      icd.validto
   FROM
      items I
         JOIN itemdetail D
            ON I.itemid = D.itemid
           AND D.propid = 13
           LEFT OUTER JOIN icd
              ON D.value = icd.code
             AND ( icd.validfrom <= '2012-12-06'
                  OR icd.validfrom IS NULL )
             AND ( icd.validto >= '2012-12-06'
                  OR icd.validto IS NULL )
         LEFT OUTER JOIN edi_icdcodes C
            ON I.itemid = C.itemid
   WHERE  
          I.itemtype = 'I'
      AND I.deleteflag = 0
      AND I.keyname = 'Assessments'
      AND I.itemname LIKE 'A%'
   ORDER BY 
      I.itemname ASC 
   LIMIT 
      0,6;  

注意...如果ICD表在创建记录时始终具有从/到日期的值，则无需测试NULL，但可以理解为什么通过左联接并在where处放置了该值条款。 因此，该部分可能简化为

   LEFT OUTER JOIN icd
      ON D.value = icd.code
     AND icd.validfrom <= '2012-12-06'
     AND icd.validto >= '2012-12-06'