查询排序

顺序

SELECT * FROM `website` ORDER BY `id` ASC;

SELECT * FROM `runoob_tbl` ORDER BY `runoob_submission_date` ASC;

倒序

SELECT * FROM `website` ORDER BY `id` DESC;

SELECT * FROM `runoob_tbl` ORDER BY `runoob_submission_date` DESC;

去重

单字段去重

SELECT DISTINCT `runoob_submission_date` FROM `runoob_tbl`;

分组去重

SELECT * FROM `runoob_tbl` GROUP BY `runoob_submission_date`;

SELECT * FROM `runoob_tbl` GROUP BY `runoob_submission_date` ORDER BY `runoob_submission_date` ASC;

计数

计数(不含null)

SELECT COUNT(`runoob_submission_date`) AS 'total' FROM `runoob_tbl`;

去重计数(不含null)

SELECT COUNT(DISTINCT `runoob_submission_date`) AS 'total' FROM `runoob_tbl`;

分组计数(含null)

SELECT `runoob_submission_date` AS 'date', COUNT(*) as 'count' FROM `runoob_tbl` GROUP BY `runoob_submission_date`;

表数据总条目数

SELECT COUNT(*) AS 'total' FROM `runoob_tbl`;

条件查询

WHERE条件子句

SELECT * FROM `runoob_tbl` WHERE `runoob_id` = 1;

SELECT * FROM `runoob_tbl` WHERE `runoob_author` LIKE '%.com%';

SELECT * FROM `runoob_tbl` WHERE `runoob_submission_date` < "2015-05-02 00:00:00";

组合查询

不带重复的组合查询

SELECT `country` FROM `website`

UNION

SELECT `country` FROM `apps`

ORDER BY `country`;

带重复的组合查询

SELECT `country` FROM `website`

UNION ALL

SELECT `country` FROM `apps`

ORDER BY `country`;

联合查询

SELECT

a.teacher_name,

a.teacher_grader,

c.course_name,

b.class_name

FROM

t_teacher a

INNER JOIN

t_class b

INNER JOIN

t_course c

INNER JOIN

t_teacher_class z ON z.teacher_id = a.id

AND z.class_id = b.id

AND a.course_id = c.id

WHERE

a.teacher_name LIKE '%董%';