我有两张 table 。一个是用户，它有字段 uid 和 name。另一个表是 users_roles，它有字段 uid 和 rid(角色 id)。

我想检索不具有任何一组提供的角色的用户列表。

例如:

uid | name
----------
1   | BOB
2   | DAVE
3   | JOHN

USERS_ROLES:

uid | rid
---------
1   | 1
1   | 2
1   | 3
2   | 1
3   | 1

我希望能够只查询没有特定 rid 集的用户。例如，排除 rids 2 和 3 的查询应返回 DAVE 和 JOHN，或者排除 rids (1,3) 的查询应返回 nobody。

最佳答案

使用反连接模式的查询有时是最有效的:

SELECT u.uid
     , u.name
  FROM users u
  LEFT
  JOIN users_roles r
    ON r.uid = u.uid
   AND r.rid IN (2,3)
 WHERE r.uid IS NULL

反连接模式是做一个 LEFT [outer] JOIN user_roles表以拉回所有匹配的行，并从 users 中获取行没有匹配的行。 “技巧”是用 WHERE 子句中的谓词排除所有匹配的行，该谓词从具有匹配项的用户中消除所有行。

可以使用 NOT EXISTS 相关子查询获得等效的结果集:

SELECT u.uid
     , u.name
  FROM users u
 WHERE NOT EXISTS 
       ( SELECT 1 
           FROM users_roles r
          WHERE r.uid = u.uid
            AND r.rid IN (2,3)
       )

另一种方法是使用 NOT IN ，尽管这有时效率较低。性能取决于很多因素。优化器有可能为这些查询中的每一个生成不同的执行计划。

无论如何，为了获得最佳性能，您需要一个索引... ON users_roles (uid)或 ON users_roles (uid,rid) .

跟进:

在我的 MySQL 5.1.34 服务器上进行的性能测试表明，反连接查询的速度几乎是等效的 NOT EXISTS 和 NOT IN 查询的两倍。 (1.091 秒与 2.066 秒和 2.020 秒)

-- setup and populate test tables
CREATE TABLE t_users
( uid    INT UNSIGNED NOT NULL PRIMARY KEY
, `name` VARCHAR(50)
) ENGINE=INNODB DEFAULT CHARSET=latin1 ;

CREATE TABLE t_users_roles
( uid INT UNSIGNED NOT NULL
, rid INT UNSIGNED NOT NULL
, PRIMARY KEY (uid,rid)
) ENGINE=INNODB DEFAULT CHARSET=latin1;

ALTER TABLE t_users_roles ADD CONSTRAINT FK_t_users_roles_t_users FOREIGN KEY (uid) REFERENCES t_users (uid);

CREATE INDEX t_users_ix1 ON t_users (uid,`name`);

CREATE INDEX t_users_roles_ix1 ON t_users_roles (rid,uid);

INSERT INTO t_users (uid,`name`)
SELECT d.d*100000+e.d*10000+u.d*1000+h.d*100+t.d*10+o.d+1 AS uid
     , CONCAT('NAME',LPAD(d.d*100000+e.d*10000+u.d*1000+h.d*100+t.d*10+o.d+1,8,'-')) AS `name`
  FROM (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) o
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) h
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) u
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) e
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) d 
;

-- 1000000 row(s) affected.

INSERT INTO t_users_roles (uid,rid)
SELECT d.d*100000+e.d*10000+u.d*1000+h.d*100+t.d*10+o.d+1 AS uid
     , r.rid
  FROM (SELECT 1 AS rid UNION ALL SELECT 2 UNION ALL SELECT 3) r
 CROSS
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) o
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) t
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) h
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) u
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) e
  JOIN (SELECT 0 AS d UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) d
 WHERE (d.d*100000+e.d*10000+u.d*1000+h.d*100+t.d*10+o.d+1) % 100000 <> 0
;
-- 2999970 row(s) affected

OPTIMIZE TABLE t_users;
OPTIMIZE TABLE t_users_roles;

SHOW STATUS LIKE 'Qcache_hits' ;
-- Variable_name  Value    
-- -------------  ---------
-- Qcache_hits    1117342  

SHOW VARIABLES LIKE 'version' ; 
-- Variable_name  Value       
-- -------------  ------------
-- version        5.1.53-log

-- table size from the file system
$ du -sh DATA/test/t_users*.ibd
72M     DATA/test/t_users.ibd
133M    DATA/test/t_users_roles.ibd


-- anti-join query
SELECT SQL_NO_CACHE u.uid
     , u.name
  FROM t_users u
  LEFT
  JOIN t_users_roles r
    ON r.uid = u.uid
   AND r.rid IN (2,3)
 WHERE r.uid IS NULL ;

-- Exec: 1.095 sec
-- Exec: 1.090 sec
-- Exec: 1.091 sec
-- Exec: 1.087 sec
-- Exec: 1.090 sec
-- avg 5 executions: 1.091 sec    


-- not exists query
SELECT SQL_NO_CACHE u.uid
     , u.name
  FROM t_users u
 WHERE NOT EXISTS
       ( SELECT 1
           FROM t_users_roles r
          WHERE r.uid = u.uid
            AND r.rid IN (2,3)
       ) ;

-- Exec: 2.071 sec
-- Exec: 2.066 sec
-- Exec: 2.059 sec
-- Exec: 2.065 sec
-- Exec: 2.070 sec
-- avg 5 executions: 2.066 sec

-- not in query
SELECT SQL_NO_CACHE u.uid
     , u.name
  FROM t_users u
 WHERE u.uid NOT IN
       ( SELECT r.uid
           FROM t_users_roles r
          WHERE r.uid IS NOT NULL
            AND r.rid IN (2,3)
       ) ;

-- Exec: 2.022 sec 
-- Exec: 2.023 sec 
-- Exec: 2.014 sec
-- Exec: 2.026 sec
-- Exec: 2.016 sec
-- avg 5 executions: 2.020 sec

SHOW STATUS LIKE 'Qcache_hits' ;
-- Variable_name  Value    
-- -------------  ---------
-- Qcache_hits    1117342  

EXPLAIN output for three statements:

-- ANTI JOIN
id  select_type         table   type            possible_keys              key          key_len  ref       rows   filtered  Extra                                 
--  ------------------  ------  --------------  -------------------------  -----------  -------  -----  -------  --------  ------------------------------------
 1  SIMPLE              u       index                                      t_users_ix1  57              1000423    100.00  Using index
 1  SIMPLE              r       ref             PRIMARY,t_users_roles_ix1  PRIMARY      4        u.uid        1    100.00  Using where; Using index; Not exists

-- NOT EXISTS
id  select_type         table   type            possible_keys              key          key_len  ref       rows  filtered  Extra                     
--  ------------------  ------  --------------  -------------------------  -----------  -------  -----  -------  --------  --------------------------
 1  PRIMARY             u       index                                      t_users_ix1  57              1000423    100.00  Using where; Using index
 2  DEPENDENT SUBQUERY  r       ref             PRIMARY,t_users_roles_ix1  PRIMARY      4        u.uid        1    100.00  Using where; Using index

-- NOT IN
id  select_type         table   type            possible_keys              key          key_len  ref        rows  filtered  Extra                     
--  ------------------  ------  --------------  -------------------------  -----------  -------  ------  -------  --------  --------------------------
 1  PRIMARY             u       index                                      t_users_ix1  57               1000423    100.00  Using where; Using index
 2  DEPENDENT SUBQUERY  r       index_subquery  PRIMARY,t_users_roles_ix1  PRIMARY      4        func          1    100.00  Using index; Using where

关于MYSQL:如果一个连接行符合条件，则排除多行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14710632/