列转行:利用max(case when then)
SELECT
`name`,
MAX(
CASE
WHEN course='语文' THEN
score
END
) AS 语文,
MAX(
CASE
WHEN course='数学' THEN
score
END
) AS 数学,
MAX(
CASE
WHEN course='英语' THEN
score
END
) AS 英语
FROM
student
GROUP BY `name`
;
合并字段显示:利用group_cancat(course,”:”,”score”)
SELECT
`name`,
GROUP_CONCAT(course, ":", score) AS 成绩
FROM
student
GROUP BY
`name`;
-- -- -- -- -- -- -- --- - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --- - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --- - -- -- -- -- -- -- -- -- -- -- -- -- -
-- 合并字段显示 : 去重、排序
SELECT rid,GROUP_CONCAT(DISTINCT gid ORDER BY gid)
FROM gt_lighting.res_lights
GROUP BY rid;
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
多来点面试题:
计算各班级及格人数:
SELECT class,SUM(CASE WHEN score >= 60 THEN 1 END) AS '及格',SUM(CASE WHEN score < 60 THEN 1 END) AS '不及格'
FROM gradeTable
GROUP BY class;
或者:
SELECT succ.class,succ.su AS '及格',fail.fa AS '不及格' FROM
(
SELECT class,COUNT() AS su
FROM gradeTable
WHERE score >=
GROUP BY class
) AS succ,
(
SELECT class,COUNT() AS fa
FROM gradeTable
WHERE score <
GROUP BY class
) AS fail
WHERE succ.class = fail.class;
Console :
啦啦啦
啦啦啦