mysql 分组前3条

测试数据

DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp`  (
  `empno` decimal(4, 0) NOT NULL,
  `ename` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `job` varchar(9) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `mgr` decimal(4, 0) NULL DEFAULT NULL,
  `hiredate` datetime(0) NULL DEFAULT NULL,
  `sal` decimal(7, 2) NULL DEFAULT NULL,
  `comm` decimal(7, 2) NULL DEFAULT NULL,
  `deptno` decimal(2, 0) NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of emp
-- ----------------------------
INSERT INTO `emp` VALUES (7369, 'SMITH', 'CLERK', 7902, '1980-12-17 00:00:00', 800.00, NULL, 20);
INSERT INTO `emp` VALUES (7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20 00:00:00', 1600.00, 300.00, 30);
INSERT INTO `emp` VALUES (7521, 'WARD', 'SALESMAN', 7698, '1981-02-22 00:00:00', 1250.00, 500.00, 30);
INSERT INTO `emp` VALUES (7566, 'JONES', 'MANAGER', 7839, '1981-04-02 00:00:00', 2975.00, NULL, 20);
INSERT INTO `emp` VALUES (7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28 00:00:00', 1250.00, 1400.00, 30);
INSERT INTO `emp` VALUES (7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01 00:00:00', 2850.00, NULL, 30);
INSERT INTO `emp` VALUES (7782, 'CLARK', 'MANAGER', 7839, '1981-06-09 00:00:00', 2450.00, NULL, 10);
INSERT INTO `emp` VALUES (7788, 'SCOTT', 'ANALYST', 7566, '1982-12-09 00:00:00', 3000.00, NULL, 20);
INSERT INTO `emp` VALUES (7839, 'KING', 'PRESIDENT', NULL, '1981-11-17 00:00:00', 5000.00, NULL, 10);
INSERT INTO `emp` VALUES (7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08 00:00:00', 1500.00, 0.00, 30);
INSERT INTO `emp` VALUES (7876, 'ADAMS', 'CLERK', 7788, '1983-01-12 00:00:00', 1100.00, NULL, 20);
INSERT INTO `emp` VALUES (7900, 'JAMES', 'CLERK', 7698, '1981-12-03 00:00:00', 950.00, NULL, 30);
INSERT INTO `emp` VALUES (7902, 'FORD', 'ANALYST', 7566, '1981-12-03 00:00:00', 3000.00, NULL, 20);
INSERT INTO `emp` VALUES (7934, 'MILLER', 'CLERK', 7782, '1982-01-23 00:00:00', 1300.00, NULL, 10);

# 开启外键约束
# SET FOREIGN_KEY_CHECKS = 1;
# 关闭外键约束
# SET FOREIGN_KEY_CHECKS = 0;

　查询

SELECT
    * 
FROM
    emp e 
WHERE
    ( SELECT count( 1 ) FROM emp WHERE deptno = e.deptno AND e.sal < sal ) < 3 
ORDER BY
    deptno,
    sal

结果

                                                             工资                部门
+-------+--------+-----------+------+---------------------+---------+--------+--------+
| empno | ename  | job       | mgr  | hiredate            | sal     | comm   | deptno |
+-------+--------+-----------+------+---------------------+---------+--------+--------+
|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 00:00:00 | 1300.00 |   NULL |     10 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 00:00:00 | 2450.00 |   NULL |     10 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 |   NULL |     10 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 00:00:00 | 2975.00 |   NULL |     20 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1982-12-09 00:00:00 | 3000.00 |   NULL |     20 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 00:00:00 | 3000.00 |   NULL |     20 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 00:00:00 | 1500.00 |   0.00 |     30 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 00:00:00 | 2850.00 |   NULL |     30 |
+-------+--------+-----------+------+---------------------+---------+--------+--------+