MySQL quick check
Because I often forget some mysql statements, keywords, operations, etc. in my daily work and study, I recently took some time to write the following content about mysql. It's like a dictionary
Reset mysql password
Data type
operator
Common functions Basic operations of
data integrity
database
This article operates
on data in the table
Subquery
Multi-table connection
Index
view
Preprocessing SQL statements
Custom functions and stored procedures
Programming in MySQL
Operations on the table itself
View table
view all
1 show tables;
2 SHOW TABLE STATUS
[{
FROM | IN} 数据库名]
[LIKE 'pattern' | WHERE where筛选表达式]
show table status类似show tables，但会显示更多信息
mysql> show table status from sys;
+-----------------------------------------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+-----------------------------------------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+--------------------+----------+----------------+---------+
| host_summary | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 2021-03-08 19:30:21 | NULL | NULL | NULL | NULL | NULL | VIEW |
| host_summary_by_file_io | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 2021-03-08 19:30:21 | NULL | NULL | NULL | NULL | NULL | VIEW |
...
# 使用show tables时
mysql> use sys;
mysql> show tables;
+-----------------------------------------------+
| Tables_in_sys |
+-----------------------------------------------+
| host_summary |
| host_summary_by_file_io |
| host_summary_by_file_io_type |
...
View table structure
1 describe tb_name;
desc是describe的缩写
# 查看表结构详细信息
2 show create table 表名;
mysql> use sys;
mysql> desc host_summary;
+------------------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+---------------+------+-----+---------+-------+
| host | varchar(255) | YES | | NULL | |
...
mysql> show create table host_summary;
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View | character_set_client | collation_connection |
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| host_summary | CREATE ALGORITHM=TEMPTABLE DEFINER=`mysql.sys`@`localhost` SQL SECURITY INVOKER VIEW `host_summary` (`host`,`statements`,`statement_latency`,`statement_avg_latency`,`table_scans`,`file_ios`,`file_io_latency`,`current_connections`,`total_connections`,`unique_users`,`current_memory`,`total_memory_allocated`) AS select if((`performance_schema`.`accounts`.`HOST` is null),'background',`performance_schema`.`accounts`.`HOST`) AS `host`,sum(`stmt`.`total`) AS `statements`,format_pico_time(sum(`stmt`.`total_latency`)) AS `statement_latency`,format_pico_time(ifnull((sum(`stmt`.`total_latency`) / nullif(sum(`stmt`.`total`),0)),0)) AS `statement_avg_latency`,sum(`stmt`.`full_scans`) AS `table_scans`,sum(`io`.`ios`) AS `file_ios`,format_pico_time(sum(`io`.`io_latency`)) AS `file_io_latency`,sum(`performance_schema`.`accounts`.`CURRENT_CONNECTIONS`) AS `current_connections`,sum(`performance_schema`.`accounts`.`TOTAL_CONNECTIONS`) AS `total_connections`,count(distinct `performance_schema`.`accounts`.`USER`) AS `unique_users`,format_bytes(sum(`mem`.`current_allocated`)) AS `current_memory`,format_bytes(sum(`mem`.`total_allocated`)) AS `total_memory_allocated` from (((`performance_schema`.`accounts` join `x$host_summary_by_statement_latency` `stmt` on((`performance_schema`.`accounts`.`HOST` = `stmt`.`host`))) join `x$host_summary_by_file_io` `io` on((`performance_schema`.`accounts`.`HOST` = `io`.`host`))) join `x$memory_by_host_by_current_bytes` `mem` on((`performance_schema`.`accounts`.`HOST` = `mem`.`host`))) group by if((`performance_schema`.`accounts`.`HOST` is null),'background',`performance_schema`.`accounts`.`HOST`) | utf8mb4 | utf8mb4_0900_ai_ci |
+--------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
1 row in set (0.01 sec)
Add table
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] 表名
(字段名 数据类型 [完整性约束],...)
如果指定temporary，则创建的是临时表，
会话结束会自动释放，并且show tables看不到该表
mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)
mysql> create table t1(id int primary key, name char(10));
Query OK, 0 rows affected (0.12 sec)
mysql> desc t1;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | char(10) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
Delete table
DROP [TEMPORARY] TABLE [IF EXISTS]
表名1 [, 表名2] ...
[RESTRICT | CASCADE]
The RESTRICT and CASCADE keywords have no effect. These two keywords are used to facilitate portability from other databases.
Deleting a table will also delete the data in the table.
drop table t1; # 删除t1表
Modify table
Modify fields in table
ALTER TABLE 表名
[alter_option [, alter_option] ...]
[partition_options]
alter_option: alter操作，如增加、删除、修改等，下面详细介绍。
partition_options: 分区操作
Add field
ALTER TABLE 表名
ADD [COLUMN] 要增加的字段名 数据类型 完整性约束
[FIRST | AFTER 表中存在的字段名]
# 例如
alter table t1
add column sex char(1) not null default '女'
after name;
first and after specify the position of the new field. If not written, it will be added at the end by default. (Note: Do not add any characters after first)
You can also add multiple fields at the same time
ALTER TABLE 表名
ADD [COLUMN] 要增加的字段名 数据类型 完整性约束[,...]
# 例如
alter table t1
add sex char(1) default '男',
age int;
Add/remove integrity constraints for fields in the table
ALTER TABLE 表名
# 添加主键
ADD PRIMARY KEY(字段名,...)
# 为字段指定唯一约束
| ADD UNIQUE (字段名,...)
# 添加外键
| ADD FOREIGN KEY(字段名,...)
references 另一个表名(字段名,...)
# 为字段增加check约束
| ADD CHECK (expr)
# 为字段删除check
| DROP CHECK symbol
# 去除字段主键约束
| DROP PRIMARY KEY
# 去除字段外键约束
| DROP FOREIGN KEY fk_symbol
Modify fields
changeModify field
ALTER TABLE 表名
CHANGE [COLUMN] 旧字段名 新字段名 数据类型 完整性约束
[FIRST | AFTER 表中字段名]
mysql> desc t1;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | char(10) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> desc t1;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | char(10) | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> alter table t1
-> change name xingming varchar(12) not null
-> first; # 将name改成xingming并放在首位
Query OK, 0 rows affected (0.26 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t1;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| xingming | varchar(12) | NO | | NULL | |
| id | int | NO | PRI | NULL | |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
modify modify field
ALTER TABLE 表名
MODIFY [COLUMN]
字段名 新数据类型 [新完整性约束]
[FIRST | AFTER 字段名]
alter table t1
modify column
xingming char(10) unique
after id;
mysql> alter table t1
-> modify column
-> xingming char(10) unique
-> after id;
Query OK, 0 rows affected (0.21 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t1;
+----------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| xingming | char(10) | YES | UNI | NULL | |
+----------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
renameRename field
ALTER TABLE 表名
RENAME COLUMN 旧字段名 TO 新字段名
mysql> alter table t1 rename column xingming to name;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc t1;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | char(10) | YES | UNI | NULL | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
Delete field
ALTER TABLE 表名 DROP [COLUMN] 字段名
alter table t1 drop name;
Modify table name
ALTER TABLE 表名 RENAME [TO | AS] 新表名
mysql> alter table t1 rename to t2;
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t2 |
+----------------+
1 row in set (0.00 sec)
mysql> alter table t2 rename as t1;
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1 |
+----------------+
1 row in set (0.00 sec)