1 查询全部字段mysql
1.1 使用*通配符查询全部字段sql
SELECT * FROM 表名app
1.2 在SELECT语句中指定全部字段函数
SELECT id,name from users；ui
2 查询指定字段code
2.1 查询单个字段排序
SELECT 列名 FROM 表名；it
2.2 查询多个字段class
SELECT 列名1，列名2，列名3 ...列名n from 表名select
2.3 查询指定记录
SELECT 字段名1，字段名2，...，字段名n FROM 表名 where 查询条件
2.4 带in关键字的查询
mysql> SELECT f_id from fruits where f_name in(apple, orange);
ERROR 1054 (42S22): Unknown column 'apple' in 'where clause'
mysql> SELECT f_id from fruits where f_name in('apple','orange');
+------+
| f_id |
+------+
| a1 |
| bs1 |
+------+
2 rows in set (0.00 sec)
2.5 带between and的范围查询
mysql> select f_name from fruits where f_price between 5 and 11; +------------+ | f_name | +------------+ | apple | | blackberry | +------------+ 2 rows in set (0.00 sec)
2.6 带有like的字符匹配查询
能够和like一块儿匹配使用的通配符有 % 和 _
2.6.1 百分号通配符 % 匹配任意长度的字符，甚至包括零字符 %能够放在任意位置
mysql> select f_id,s_id,f_name from fruits where f_name like '%c%'; +------+------+------------+ | f_id | s_id | f_name | +------+------+------------+ | b1 | 101 | blackberry | +------+------+------------+ 1 row in set (0.00 sec)
2.6.2 下划线通配符 _ 一次只能匹配任意一个字符
select f_id, f_name from fruits where f_name like '____e'; +------+--------+ | f_id | f_name | +------+--------+ | a1 | apple | +------+--------+ 1 row in set (0.00 sec)
2.7 查询空值
select语句中使用 is NULL 子句，能够查询字段是否为空
mysql> select f_id, f_name from fruits where province is NULL; +------+--------+ | f_id | f_name | +------+--------+ | bs1 | orange | +------+--------+ 1 row in set (0.00 sec)
2.8 带and的多条件查询
使用and链接两个甚至多个查询条件，多个条件表达式之间用and分开
mysql> select * from fruits where f_price>6 and province is NOT NULL; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | b1 | 101 | blackberry | 10.20 | ShanDong | +------+------+------------+---------+----------+ 1 row in set (0.00 sec)
2.9 带or的多条件查询
mysql> select * from fruits where f_name = 'apple' or province is NULL; +------+------+--------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+--------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | bs1 | 102 | orange | 11.20 | NULL | +------+------+--------+---------+----------+ 2 rows in set (0.00 sec)
2.10 distinct 消除重复记录
mysql> select * from fruits; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 3 rows in set (0.00 sec) mysql> select distinct s_id from fruits; +------+ | s_id | +------+ | 101 | | 102 | +------+ 2 rows in set (0.00 sec)
2.11 对查询结果排序
2.11.1 单列排序
mysql> select * from fruits order by f_price; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 3 rows in set (0.00 sec) mysql> select * from fruits order by province; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | bs1 | 102 | orange | 11.20 | NULL | | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | +------+------+------------+---------+----------+ 3 rows in set (0.00 sec)
2.11.2 多列排序
在对多列排序的时候，只有在第一列有相同值的状况下，才会对第二列进行排序。
mysql> select * from fruits; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | | b11 | 101 | apple | 4.00 | NULL | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 4 rows in set (0.00 sec) mysql> select * from fruits order by f_name; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | b11 | 101 | apple | 4.00 | NULL | | b1 | 101 | blackberry | 10.20 | ShanDong | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 4 rows in set (0.00 sec) mysql> select * from fruits order by f_name,f_price; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | b11 | 101 | apple | 4.00 | NULL | | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 4 rows in set (0.00 sec)
2.11.3 指定排序方向
DESC 降序 ASC升序
mysql> select * from fruits; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | a1 | 101 | apple | 5.20 | HeNan | | b1 | 101 | blackberry | 10.20 | ShanDong | | b11 | 101 | apple | 4.00 | NULL | | bs1 | 102 | orange | 11.20 | NULL | +------+------+------------+---------+----------+ 4 rows in set (0.00 sec) mysql> select * from fruits order by f_price DESC; +------+------+------------+---------+----------+ | f_id | s_id | f_name | f_price | province | +------+------+------------+---------+----------+ | bs1 | 102 | orange | 11.20 | NULL | | b1 | 101 | blackberry | 10.20 | ShanDong | | a1 | 101 | apple | 5.20 | HeNan | | b11 | 101 | apple | 4.00 | NULL | +------+------+------------+---------+----------+ 4 rows in set (0.00 sec)
2.12 分组查询
2.12.1 建立分组
group by关键字一般和集合函数一块儿使用，如MAX(),MIN(),COUNT(),SUM(),AVG().
mysql> select s_id,count(*) as total from fruits group by s_id; +------+-------+ | s_id | total | +------+-------+ | 101 | 3 | | 102 | 1 | +------+-------+ 2 rows in set (0.01 sec)
mysql> select s_id,count(*) as total, group_concat(f_name) from fruits group by s_id; +------+-------+------------------------+ | s_id | total | group_concat(f_name) | +------+-------+------------------------+ | 101 | 3 | apple,blackberry,apple | | 102 | 1 | orange | +------+-------+------------------------+ 2 rows in set (0.00 sec)
2.12.2 使用having过滤分组
mysql> select s_id, count(*) as total from fruits group by s_id having count(*)>1; +------+-------+ | s_id | total | +------+-------+ | 101 | 3 | +------+-------+ 1 row in set (0.00 sec)
2.12.3 在group by子句中使用with rollup
使用with rollup关键自以后，最后一行会记录一条查询出的全部记录的总和，能够用来统计记录数量。
mysql> select s_id,count(*) as total from fruits group by s_id with rollup; +------+-------+ | s_id | total | +------+-------+ | 101 | 3 | | 102 | 1 | | NULL | 4 | +------+-------+ 3 rows in set (0.01 sec)
2.12.4 多字段分组
group by name1,name2