Mysql e、 对于底部查询，我认为对于顶部查询，它将改变结果。@Johan:因为st2.相关字段不是NULL（它已经包含在ON子句中），它不会改变结果。@ypercube，所以您可以将count（afield）更改为count（*）如果您确定afield永远不会为

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e、 对于底部查询，我认为对于顶部查询，它将改变结果。@Johan:因为

st2.相关字段
不是
NULL
（它已经包含在
ON
子句中），它不会改变结果。@ypercube，所以您可以将count（afield）更改为count（*）如果您确定
afield
永远不会为
null
，明白了。Thanks@quano是，它列出了所有重复项，因为
分组依据
位于
st1.id
上，而不是位于
st1.relevant_字段
。是的，这可能会创建一个包含分组结果的临时表，因此速度与查看版本相同。但是查询计划应该说实话，这对我来说非常有效。我在一个IN（子查询）中有另一个IN（子查询），它花费了超过10分钟的时间，以至于我在等待的时候用谷歌搜索。按照您的建议，在SELECT*FROM（）中包装每个子查询将其缩短为2秒！谢谢你，我一直在想一个好办法来做这几小时了。这很有效。但愿我能给你更多的选票！这绝对应该是答案。效果非常好。一个耗时约50秒的查询现在是即时的。但愿我能投更多的票。有时候你不能使用连接，所以这是正确的答案。我想知道为什么优化器会考虑与联合相关的查询。。。不管怎样，这个技巧就像魔法一样有效。你能解释一下是什么使它成为一个相关子查询吗？我的理解是，当子查询使用一个依赖于外部查询的值时，它就会变得相关。但在这个例子中，我看不到任何相互依赖性。它将为外部查询返回的每一行提供相同的结果。我在MariaDB上实现了一个类似的示例，我看不出性能有什么影响（到目前为止），所以我想清楚地看到，什么时候需要这个
SELECT*
wrapping。
SELECT relevant_field
FROM some_table
GROUP BY relevant_field
HAVING COUNT(*) > 1

SELECT *
FROM some_table 
WHERE relevant_field IN
(
    SELECT relevant_field
    FROM some_table
    GROUP BY relevant_field
    HAVING COUNT(*) > 1
)

SELECT *
FROM some_table
WHERE relevant_field IN
(
    SELECT relevant_field
    FROM temp_view
)

SELECT *
FROM some_table
WHERE
 relevant_field in
 (
  SELECT relevant_field
  FROM some_table
  GROUP BY relevant_field
  HAVING COUNT ( * ) > 1
 );

SELECT *
FROM some_table as t1
WHERE
 t1.relevant_field in
 (
  SELECT t2.relevant_field
  FROM some_table as t2
  GROUP BY t2.relevant_field
  HAVING COUNT ( t2.relevant_field ) > 1
 );

SELECT st1.*
FROM some_table st1
inner join 
(
    SELECT relevant_field
    FROM some_table
    GROUP BY relevant_field
    HAVING COUNT(*) > 1
)st2 on st2.relevant_field = st1.relevant_field;

SELECT st1.*, st2.relevant_field FROM sometable st1
INNER JOIN sometable st2 ON (st1.relevant_field = st2.relevant_field)
GROUP BY st1.id  /* list a unique sometable field here*/
HAVING COUNT(*) > 1

SELECT * FROM sometable a WHERE EXISTS (
  SELECT 1 FROM sometable b
  WHERE a.relevant_field = b.relevant_field
  GROUP BY b.relevant_field
  HAVING count(*) > 1) 

SELECT * FROM
(
    SELECT relevant_field
    FROM some_table
    GROUP BY relevant_field
    HAVING COUNT(*) > 1
) AS subquery

SELECT *
FROM some_table
WHERE relevant_field IN
(
    SELECT * FROM
    (
        SELECT relevant_field
        FROM some_table
        GROUP BY relevant_field
        HAVING COUNT(*) > 1
    ) AS subquery
)

SELECT t1.*
FROM 
 some_table t1,
  (SELECT relevant_field
  FROM some_table
  GROUP BY relevant_field
  HAVING COUNT (*) > 1) t2
WHERE
 t1.relevant_field = t2.relevant_field;

SELECT STRAIGHT_JOIN table.field FROM table WHERE table.id IN (...)

`select DATE_FORMAT(L.TANGGAL_INPUT,'%d-%m-%y') AS TANGGAL,
      L.TRANSACTION_NUMBER AS VOUCHER,
      L.ACCOUNT_CODE,
      C.DESCRIPTION,
      L.DEBET,
      L.KREDIT 
 from (select * from tabel_buku_besar A
                where A.COMPANYAREA='$COMPANYAREA'
                      AND A.CURRENCY='$Currency'
                      AND A.ACCOUNT_CODE!='$ACCOUNT'
                      AND (A.TANGGAL_INPUT BETWEEN STR_TO_DATE('$StartDate','%d/%m/%Y') AND STR_TO_DATE('$EndDate','%d/%m/%Y'))) L 
INNER JOIN (select * from tabel_buku_besar A
                     where A.COMPANYAREA='$COMPANYAREA'
                           AND A.CURRENCY='$Currency'
                           AND A.ACCOUNT_CODE='$ACCOUNT'
                           AND (A.TANGGAL_INPUT BETWEEN STR_TO_DATE('$StartDate','%d/%m/%Y') AND STR_TO_DATE('$EndDate','%d/%m/%Y'))) R ON R.TRANSACTION_NUMBER=L.TRANSACTION_NUMBER AND R.COMPANYAREA=L.COMPANYAREA 
LEFT OUTER JOIN master_account C ON C.ACCOUNT_CODE=L.ACCOUNT_CODE AND C.COMPANYAREA=L.COMPANYAREA 
ORDER BY L.TANGGAL_INPUT,L.TRANSACTION_NUMBER`

SELECT * FROM primary_table st1
LEFT JOIN comparision_table st2 ON (st1.relevant_field = st2.relevant_field)
WHERE st2.primaryKey IS NOT NULL