sql语言参考

字段去重查询

select distinct style from music

批量修改某字段

update music set style = "ost"  where style like "%影视剧%"

先查询，再添加或修改数据字段

select * from music where language  is null

update music set language = "外国" where language is null

mysql的sql实现

mysql> alter table 国产 rename to guochan;
习惯上函数用大写，但小写也可以
mysql> select now();
select ascii('f');
返回字符串str的第一个字符的ASCII值(str是空串时返回0),总是加单引号。
select CHAR(77,121,83,86,77);

增删改查语句

MariaDB [EMP]> insert into Employees values (100,18,'aa','bb');
Query OK, 1 row affected (0.02 sec)

MariaDB [EMP]> insert into Employees values (101,19,'a2','b2');
Query OK, 1 row affected (0.02 sec)

MariaDB [EMP]> insert into Employees values (101,19,'zara','b3');
Query OK, 1 row affected (0.01 sec)

MariaDB [EMP]> insert into Employees values (105,30,'a4','b4');
Query OK, 1 row affected (0.01 sec)

MariaDB [EMP]> select * from Employees;
+-----+-----+-------+------+
| id  | age | first | last |
+-----+-----+-------+------+
| 100 |  18 | aa    | bb   |
| 101 |  19 | a2    | b2   |
| 101 |  19 | zara  | b3   |
| 105 |  30 | a4    | b4   |
+-----+-----+-------+------+
4 rows in set (0.00 sec)

MariaDB [EMP]> UPDATE Employees SET id=102 WHERE first='zara';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [EMP]> select * from Employees;
+-----+-----+-------+------+
| id  | age | first | last |
+-----+-----+-------+------+
| 100 |  18 | aa    | bb   |
| 101 |  19 | a2    | b2   |
| 102 |  19 | zara  | b3   |
| 105 |  30 | a4    | b4   |
+-----+-----+-------+------+
4 rows in set (0.00 sec)

MariaDB [EMP]> delete from Employees where id=105;
MariaDB [EMP]> select * from Employees;
+-----+-----+-------+------+
| id  | age | first | last |
+-----+-----+-------+------+
| 100 |  18 | aa    | bb   |
| 101 |  19 | a2    | b2   |
| 102 |  19 | zara  | b3   |
+-----+-----+-------+------+
3 rows in set (0.00 sec)

MariaDB [EMP]> insert into Employees values(108,29,'wu','ma');
Query OK, 1 row affected (0.03 sec)

MariaDB [EMP]> insert into Employees values(109,26,'wang','wei');
Query OK, 1 row affected (0.02 sec)

MariaDB [EMP]> select * from Employees;
+-----+-----+-------+------+
| id  | age | first | last |
+-----+-----+-------+------+
| 100 |  18 | aa    | bb   |
| 101 |  19 | a2    | b2   |
| 102 |  19 | zara  | b3   |
| 108 |  29 | wu    | ma   |
| 109 |  26 | wang  | wei  |
+-----+-----+-------+------+
5 rows in set (0.00 sec)

show variables like '%FOREIGN%';
SET FOREIGN_KEY_CHECKS=0;

delete from geographical_position where type = 1
select distinct type from geographical_position

mysql> create user 'ab'@'localhost' identified by 'weeee';
mysql> select user,host,password from mysql.user;

INSERT(str,pos,len,newstr)
instr

mysql> select instr('contents','t');
+-----------------------+
| instr('contents','t') |
+-----------------------+
|                     4 |
+-----------------------+
1 row in set (0.00 sec)

mysqldump -u root -d -R --add-drop-table spa >spa.sql
sed -i '1i\use spa;' spa.sql
sed -i '1i\create database spa;' spa.sql
sed -i '1i\drop database if exists spa;' spa.sql
mysqldump -u root   --add-drop-table spa action_buttons>>spa.sql
mysqldump -u root   --add-drop-table spa menu>>spa.sql
mysqldump -u root   --add-drop-table --extended-insert=false spa tb_sequence>>spa.sql
mysqldump -u root   --add-drop-table spa role --where="id=20" >>spa.sql
mysqldump -u root   --add-drop-table spa role_button_relation --where="role_id=20" >>spa.sql
mysqldump -u root   --add-drop-table spa user_role_relation --where="role_id=20" >>spa.sql
mysqldump -u root   --add-drop-table spa system_user --where="username='admin'" >>spa.sql

-d, --no-data       No row information.
-R, --routines      Dump stored routines (functions and procedures).

select * from tb_sequence limit 0,1
limit是mysql的语法
select * from table limit m,n
其中m是指记录开始的index，从0开始，表示第一条记录
n是指从第m+1条开始，取n条。
select * from tablename limit 2,4
即取出第3条至第6条，4条记录

[root@db mysql]# mysqlshow
[root@db mysql]# mysql -e 'select user,password,host from mysql.user'
mysql> delete from user where user = '';    删除匿名用户
mysql> drop user ''@localhost ;