（简单）SQL练习14：从titles表获取按照title进行分组，注意对于重复的emp_no进行忽略

题目描述

从 titles 表获取按照 title 进行分组，每组个数大于等于2，给出 title 以及对应的数目t。 注意对于重复的 emp_no 进行忽略(即 emp_no 重复的 title 不计算，title 对应的数目 t 不增加)。

CREATE TABLE IF NOT EXISTS `titles` (
`emp_no` int(11) NOT NULL,
`title` varchar(50) NOT NULL,
`from_date` date NOT NULL,
`to_date` date DEFAULT NULL);


INSERT INTO titles VALUES(10001,'Senior Engineer','1986-06-26','9999-01-01');
INSERT INTO titles VALUES(10002,'Staff','1996-08-03','9999-01-01');
INSERT INTO titles VALUES(10003,'Senior Engineer','1995-12-03','9999-01-01');
INSERT INTO titles VALUES(10004,'Engineer','1986-12-01','1995-12-01');
INSERT INTO titles VALUES(10004,'Senior Engineer','1995-12-01','9999-01-01');
INSERT INTO titles VALUES(10005,'Senior Staff','1996-09-12','9999-01-01');
INSERT INTO titles VALUES(10005,'Staff','1989-09-12','1996-09-12');
INSERT INTO titles VALUES(10006,'Senior Engineer','1990-08-05','9999-01-01');
INSERT INTO titles VALUES(10007,'Senior Staff','1996-02-11','9999-01-01');
INSERT INTO titles VALUES(10007,'Staff','1989-02-10','1996-02-11');
INSERT INTO titles VALUES(10008,'Assistant Engineer','1998-03-11','2000-07-31');
INSERT INTO titles VALUES(10009,'Assistant Engineer','1985-02-18','1990-02-18');
INSERT INTO titles VALUES(10009,'Engineer','1990-02-18','1995-02-18');
INSERT INTO titles VALUES(10009,'Senior Engineer','1995-02-18','9999-01-01');
INSERT INTO titles VALUES(10010,'Engineer','1996-11-24','9999-01-01');
INSERT INTO titles VALUES(10010,'Engineer','1996-11-24','9999-01-01');

考察知识点

COUNT，GROUP BY，DISTINCT。

解题思路

这题的解法和上一题类似，只需要在使用 COUNT() 时添加 DISTINCT 确保 emp_no 的唯一性即可。

SELECT title, count(DISTINCT emp_no) AS t
FROM titles
GROUP BY title
HAVING t >= 2

题目来源：牛客网-SQL数据库实战题

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