MySQL常用的查询命令

MySQL常用的查询命令

author： headsen chen   2017-10-19  10:15:25

个人原创。转载请注明作者，出处，否则依法追究法律责任

1,查询现在的时间：
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2017-09-22 11:22:17 |
+---------------------+
1 row in set (0.00 sec)

2，查询主从灾备的主的server_id:
mysql> show global variables like 'server_id';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id | 1 |
+---------------+-------+
1 row in set (0.00 sec)

3,查询数据库是否开启了二进制日志：
mysql> show global variables like 'log_bin';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| log_bin | ON |
+---------------+-------+
1 row in set (0.00 sec)

4，将查询的数据作为插入内容：
mysql> insert into c2(id) select * from c1;
Query OK, 100000 rows affected (0.05 sec)
Records: 100000 Duplicates: 0 Warnings: 0

mysql> desc c1; --------------确保c1的查询出来的内容要和c2表要插入的内容在字段上一致。
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.00 sec)

5，向某张表中插入另外一张表的某个字段的所有值
mysql> create table c51(id int,name char(30));
Query OK, 0 rows affected (0.01 sec)

mysql> insert into c51(id) select * from chen.c3; （直插入id字段的值，其他字段的不插入，不插入的采取默认值：NULL或者空）
Query OK, 10000 rows affected (0.00 sec)
Records: 10000 Duplicates: 0 Warnings: 0

mysql> select count(*) from c51;
+----------+
| count(*) |
+----------+
| 10000 |
+----------+
1 row in set (0.00 sec)

mysql>

默认值为非空的name字段（加上 name char not null的情况）
| 9997 | |
| 9998 | |
| 9999 | |
| 10000 | |
+-------+------+
10000 rows in set (0.01 sec)

默认值为NULL的name字段（ name char 的情况）
| 9996 | NULL |
| 9997 | NULL |
| 9998 | NULL |
| 9999 | NULL |
| 10000 | NULL |
+-------+------+
10000 rows in set (0.00 sec)

5，将某个文件中内容导入到表中：
[root@paris mysql]# seq 1 100000 >/a/a
mysql> load data infile '/a/a' into table c1;
Query OK, 100000 rows affected (0.05 sec)
Records: 100000 Deleted: 0 Skipped: 0 Warnings: 0

mysql> select count(*) from c1;
+----------+
| count(*) |
+----------+
| 100000 |
+----------+
1 row in set (0.00 sec)

6，查看MySQL的主从复制的从设备的运行状况：
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 10.0.0.2
Master_User: haha
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: binlog.000003
Read_Master_Log_Pos: 106
Relay_Log_File: slave_relay_log.000009
Relay_Log_Pos: 248
Relay_Master_Log_File: binlog.000003
Slave_IO_Running: Yes ---------------------------------- 确保这两个线程是正确的开启状态
Slave_SQL_Running: Yes ---------------------------------- ..............................

7，互为主从的mysql的配置文件：
配置前提是两个数据库的内容是一致的。若不一致，先要手动做到一致。

10.0.0.2：[root@paris mysql]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

server_id=1
log_bin=binlog
log_bin_index=binlog.index

master_host=10.0.0.3
master_user=haha
master_password=123
relay_log=slave3_relay_log
relay_log_index=slave3_relay_log.index

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

10.0.0.3：[root@localhost mysql]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

server_id=2
master_host=10.0.0.2
master_user=haha
master_password=123
relay_log=slave_relay_log
relay_log_index=slave_relay_log.index

log_bin=binlog4
log_bin_index=binlog4.index

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

8，热备份命令总结：

全备：
[root@localhost mysql]# mysqldump -u root -p --all-databases -x >/a/all.sql
恢复：[root@localhost mysql]# mysql -u root -p </a/all.sql

实例：
[root@localhost mysql]# rm -rf *
[root@localhost mysql]# ls
[root@localhost mysql]# service mysqld start
[root@localhost mysql]# mysql -u root -p </a/all.sql
mysql> show tables;
+----------------+
| Tables_in_chen |
+----------------+
| c1 |
| c2 |
| c3 |
| c4 |
| c5 |
| c6 |
| c7 |
| c8 |
+----------------+
8 rows in set (0.00 sec) ------------- 数据未丢失

单个数据库备份：
备份：[root@localhost mysql]# mysqldump -u root -p --database chen -x >/a/chen.sql
恢复：[root@localhost mysql]# mysql -u root -p </a/chen.sql ---------------------（和全库备份的命令一样）

实例：
[root@localhost mysql]# mysqldump -u root -p --database chen -x >/a/chen.sql
mysql> drop database chen;
[root@localhost mysql]# mysql -u root -p </a/chen.sql
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| chen |
| mysql |
| test |
+--------------------+
4 rows in set (0.00 sec)

但张表的备份：
备份：[root@localhost mysql]# mysqldump -u root -p chen c1 c2 >/a/biao.sql
Enter password:
恢复：[root@localhost mysql]# mysql -u root -p chen </a/biao.sql
Enter password:

实例：
[root@localhost mysql]# mysqldump -u root -p chen c1 c2 >/a/biao.sql
mysql> drop table c1,c2;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+----------------+
| Tables_in_chen |
+----------------+
| c3 |
| c4 |
| c5 |
| c6 |
| c7 |
| c8 |
+----------------+
6 rows in set (0.00 sec)

[root@localhost mysql]# mysql -u root -p chen </a/biao.sql
Enter password:
mysql> show tables;
+----------------+
| Tables_in_chen |
+----------------+
| c1 |
| c2 |
| c3 |
| c4 |
| c5 |
| c6 |
| c7 |
| c8 |
+----------------+
8 rows in set (0.00 sec)

mysql> select count(*) from c2;
+----------+
| count(*) |
+----------+
| 100000 |
+----------+
1 row in set (0.00 sec)

9,在表中的数据全部插入原表中
mysql> insert into c1 select * from c1;
（省略values 选项，直接接源）