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    MySQL 5.7 NOT EXISTS的用法是什么[ mysql数据库 ]

    mysql数据库 时间:2024-11-26 22:17:42

    作者:文/会员上传

    简介:

    在MySQL中没有MINUS语句,要想实现MINUS语句,可以使用NOT EXISTS语句。查看测试表中的数据mysql> select * from person;| MSISDN | IMEI| IMSI|| +3301000000000 | 1299800000

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    在MySQL中没有MINUS语句,要想实现MINUS语句,可以使用NOT EXISTS语句。

    查看测试表中的数据
    mysql> select * from person;

    | MSISDN | IMEI| IMSI|

    | +3301000000000 | 129980000000000 | 208011000000000 |
    | +3301000000001 | 129980000000100 | 208011000000001 |
    | +3301000000002 | 129980000000200 | 208011000000002 |
    | +3301000000003 | 129980000000300 | 208011000000003 |
    | +3301000000004 | 129980000000400 | 208011000000004 |
    | +3301000000005 | 129980000000500 | 208011000000005 |
    | +3301000000006 | 129980000000600 | 208011000000006 |
    | +3301000000007 | 129980000000700 | 208011000000007 |

    8 rows in set (0.00 sec)
    mysql> select * from card;

    | IMSI| MSISDN | IMEI|

    | 208011000000000 | +3301000000000 | 129980000000000 |
    | 208011000000001 | +3301000000001 | 129980000000100 |
    | 208011000000002 | +3301000000002 | 129980000000200 |
    | 208011000000003 | +3301000000003 | 129980000000300 |
    | 208011000000004 | +3301000000004 | 129980000000400 |
    | 208011000000005 | +3301000000005 | 129980000000500 |
    | 208011000000006 | +3301000000006 | 129980000000600 |
    | 208011000000007 | +3301000000007 | 129980000000700 |
    | 208011000000008 | +3301000000008 | 129980000000800 |
    | 208011000000009 | +3301000000009 | 129980000000900 |

    10 rows in set (0.00 sec)

    查询出在card中存在,但是在person中不存在的某一列MSISDN。

    mysql> select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);

    | IMSI| MSISDN | IMEI|

    | 208011000000008 | +3301000000008 | 129980000000800 |
    | 208011000000009 | +3301000000009 | 129980000000900 |

    2 rows in set (0.00 sec)

    查看执行计划
    mysql> explain select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);

    | id | select_type| table | partitions | type| possible_keys | key | key_len | ref| rows | filtered | Extra|

    | 1 | PRIMARY| a | NULL| ALL| NULL | NULL| NULL| NULL |10 |100.00 | Using where |
    | 2 | DEPENDENT SUBQUERY | b | NULL| eq_ref | PRIMARY| PRIMARY | 20 | fire.a.MSISDN |1 |100.00 | Using where; Using index |

    2 rows in set, 2 warnings (0.00 sec)

    通过执行计划,card表使用了全表扫描,person表使用了主键索引
    mysql> show keys from card;

    | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

    | card | 0 | PRIMARY |1 | IMSI| A | 12 | NULL | NULL| | BTREE | ||

    6 rows in set (0.00 sec)
    mysql> show keys from person;

    | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

    | person | 0 | PRIMARY |1 | MSISDN | A |8 | NULL | NULL| | BTREE | ||

    1 row in set (0.00 sec)

    由于两张表的主键不是相同列,创建索引进行测试,发现card表始终无法使用索引扫描
    mysql> create index idx_card_msisdn on card(msisdn);
    Query OK, 0 rows affected (0.22 sec)
    Records: 0 Duplicates: 0 Warnings: 0
    mysql> explain select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);

    | id | select_type| table | partitions | type| possible_keys | key | key_len | ref| rows | filtered | Extra|

    | 1 | PRIMARY| a | NULL| ALL| NULL | NULL| NULL| NULL |10 |100.00 | Using where |
    | 2 | DEPENDENT SUBQUERY | b | NULL| eq_ref | PRIMARY| PRIMARY | 20 | fire.a.MSISDN |1 |100.00 | Using where; Using index |

    2 rows in set, 2 warnings (0.00 sec)

    mysql> create index idx_card_msisdn_imsi on card(msisdn,imsi);
    Query OK, 0 rows affected (0.06 sec)
    Records: 0 Duplicates: 0 Warnings: 0

    mysql> explain select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);


    | id | select_type| table | partitions | type| possible_keys | key | key_len | ref| rows | filtered | Extra|

    | 1 | PRIMARY| a | NULL| ALL| NULL | NULL| NULL| NULL |10 |100.00 | Using where |
    | 2 | DEPENDENT SUBQUERY | b | NULL| eq_ref | PRIMARY| PRIMARY | 20 | fire.a.MSISDN |1 |100.00 | Using where; Using index |

    2 rows in set, 2 warnings (0.00 sec)

    mysql> create index idx_card_imsi_msisdn on card(imsi,msisdn);
    Query OK, 0 rows affected (0.06 sec)
    Records: 0 Duplicates: 0 Warnings: 0
    mysql> explain select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);

    | id | select_type| table | partitions | type| possible_keys | key | key_len | ref| rows | filtered | Extra|
    +----+--------------------+-------+------------+--------+---------------+---------+---------+---------------+------+----------+--------------------------+
    | 1 | PRIMARY| a | NULL| ALL| NULL | NULL| NULL| NULL |10 |100.00 | Using where |
    | 2 | DEPENDENT SUBQUERY | b | NULL| eq_ref | PRIMARY| PRIMARY | 20 | fire.a.MSISDN |1 |100.00 | Using where; Using index |
    +----+--------------------+-------+------------+--------+---------------+---------+---------+---------------+------+----------+--------------------------+
    2 rows in set, 2 warnings (0.00 sec)

    mysql> explain select * from card a where not exists(select * from person b where a.MSISDN=b.MSISDN);
    +----+--------------------+-------+------------+--------+---------------+---------+---------+---------------+------+----------+--------------------------+
    | id | select_type| table | partitions | type| possible_keys | key | key_len | ref| rows | filtered | Extra|

    | 1 | PRIMARY| a | NULL| ALL| NULL | NULL| NULL| NULL |10 |100.00 | Using where |
    | 2 | DEPENDENT SUBQUERY | b | NULL| eq_ref | PRIMARY| PRIMARY | 20 | fire.a.MSISDN |1 |100.00 | Using where; Using index |

    2 rows in set, 2 warnings (0.00 sec)

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