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items表中的多列columnType，deleteFlag，keyName，itemName上有索引IX_items_itemType_deleteFlag_keyName_itemName，并且在join和where子句中使用的其他表的列上也有索引。

那我怎样才能提高查询效果？

由于

Answer 1

你在那里做什么，就是你使用一个基本的表，然后你做一些'加入'，只有在你做'你'的请求之后。要快速，请尝试将您的条件包含在“联接”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

我会根据用于where子句和order by的多个键列在item表上有一个索引。我会在前面的位置设置最小结果的索引。例如，您专门寻找＆＃34;评估＆＃34;。如果您的表有100万条记录，其中600k是项目类型＆＃34;我＆＃34;，但只有5k是＆＃34;评估＆＃34;，那么预先最小的部分可能更适合您的查询处理。

我想要你的：

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，则您不需要测试NULL，但是通过左连接了解为什么会这样做并放入where子句。因此，该部分可能会简化为

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

mysql查询需要很长时间才能执行

2 个答案: