Question

SELECT GV.ID
     , XS.SymbolId
     , GS.ID
     , XS.SymbolExchangeId
     , XS.IssueId
     , GE.ID
     , XD.ACTIVE
     , XD.ExchangeId 
  FROM TB_GDS_SECURITY GS
     , WSOD_Vanilla.WSOD_XrefIssueSymbols XS
     , WSOD_Vanilla.WSOD_XrefIssueData XD
     , TB_GDS_EXCHANGE GE
     , TB_GDS_VENDOR GV 
 WHERE XD.CompositeIssueID = GS.ISSUE_ID_TEMP 
   AND XD.IssueId = XS.IssueId 
   AND XD.ACTIVE = 'True' 
   AND GV.VENDOR_SHORT_NAME = XS.SymbolsetId 
   AND GE.EXCHANGE_SHORT_NAME = XD.ExchangeId 
   AND NOT EXISTS (SELECT ID 
                     FROM TB_GDS_VENDOR_VENUE_SYMBOL VVS
                    WHERE VVS.ISSUE_ID = XS.IssueId 
                      AND (SELECT ID 
                             FROM TB_GDS_VENDOR GV 
                            WHERE GV.VENDOR_SHORT_NAME = XS.SymbolsetId
                          )
                  );

此特定查询需要一分多钟。我希望它能在更短的时间内完成。

解释说明如下：

mysql> EXPLAIN SELECT GV.ID, XS.SymbolId, GS.ID, XS.SymbolExchangeId, XS.IssueId, GE.ID, XD.ACTIVE, XD.ExchangeId FROM TB_GDS_SECURITY GS, WSOD_Vanilla.WSOD_XrefIssueSymbols XS, WSOD_Vanilla.WSOD_XrefIssueData XD, TB_GDS_EXCHANGE GE, TB_GDS_VENDOR GV WHERE XD.CompositeIssueID = GS.ISSUE_ID_TEMP AND XD.IssueId = XS.IssueId AND XD.ACTIVE = 'True' AND GV.VENDOR_SHORT_NAME=XS.SymbolsetId AND GE.EXCHANGE_SHORT_NAME = XD.ExchangeId AND NOT exists (SELECT ID FROM TB_GDS_VENDOR_VENUE_SYMBOL VVS
    -> WHERE VVS.ISSUE_ID = XS.IssueId AND (SELECT ID FROM TB_GDS_VENDOR GV WHERE GV.VENDOR_SHORT_NAME = XS.SymbolsetId)); 
+----+--------------------+-------+------+--------------------------------------------------------+-----------------------------+---------+----------------------------------+---------+------------------------------------+
| id | select_type        | table | type | possible_keys                                          | key                         | key_len | ref                              | rows    | Extra                              |
+----+--------------------+-------+------+--------------------------------------------------------+-----------------------------+---------+----------------------------------+---------+------------------------------------+
|  1 | PRIMARY            | XD    | ref  | WSOD_XrefIssueData_UINDX1,WSOD_XrefIssueData_INDX1     | WSOD_XrefIssueData_INDX1    | 21      | const                            | 3981788 | Using index condition; Using where |
|  1 | PRIMARY            | GE    | ref  | TB_GDS_EXCHANGE_INDX1                                  | TB_GDS_EXCHANGE_INDX1       | 63      | WSOD_Vanilla.XD.ExchangeId       |       1 | Using where; Using index           |
|  1 | PRIMARY            | GS    | ref  | TB_GDS_SECURITY_INDX1                                  | TB_GDS_SECURITY_INDX1       | 5       | WSOD_Vanilla.XD.CompositeIssueID |       1 | Using where; Using index           |
|  1 | PRIMARY            | XS    | ref  | PRIMARY                                                | PRIMARY                     | 8       | WSOD_Vanilla.XD.IssueId          |       1 | Using where                        |
|  1 | PRIMARY            | GV    | ref  | TB_GDS_VENDOR_INDX1                                    | TB_GDS_VENDOR_INDX1         | 62      | WSOD_Vanilla.XS.SymbolsetId      |       1 | Using where; Using index           |
|  2 | DEPENDENT SUBQUERY | VVS   | ref  | TB_GDS_VVENUE_SYMBOL_UINDX1,TB_GDS_VVENUE_SYMBOL_INDX2 | TB_GDS_VVENUE_SYMBOL_UINDX1 | 5       | WSOD_Vanilla.XS.IssueId          |       3 | Using where; Using index           |
|  3 | DEPENDENT SUBQUERY | GV    | ref  | TB_GDS_VENDOR_INDX1                                    | TB_GDS_VENDOR_INDX1         | 62      | WSOD_Vanilla.XS.SymbolsetId      |       1 | Using where; Using index           |
+----+--------------------+-------+------+--------------------------------------------------------+-----------------------------+---------+----------------------------------+---------+------------------------------------+
7 rows in set (0.01 sec)

优化后仍然需要大约1.35分钟才能执行。请帮帮我。

Answer 1

根据其他地方的评论，你没有向我们展示索引定义。

这里的沼泽成本很可能是NOT EXISTS子条款。 MySQL没有很好地处理推送预测，你也有一个笛卡尔积。我很难理解这实际上是做什么的。 MySQL（确实没有我熟悉的DBMS）可以有效地使用NOT EXISTS或＆lt;＆gt;的索引。或者不喜欢。嵌套的嵌套查询似乎不提供任何功能，因为外部查询中的这些表之间已经有显式连接：

WHERE...AND GV.VENDOR_SHORT_NAME = XS.SymbolsetId...
AND NOT EXISTS ( [a condition] AND
   SELECT ID FROM TB_GDS_VENDOR GV 
   WHERE GV.VENDOR_SHORT_NAME = XS.SymbolsetId

你唯一的过滤除了连接和这个丑陋的NOT EXISTS是“AND XD.ACTIVE ='True'” - 如果这个列只有2/3值，那么使用索引的效率可能非常低。

Mysql Join语句查询的优化

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