MySQL common commands
1. Check the space occupied by each database
select table_schema,concat(round(sum((DATA_LENGTH+INDEX_LENGTH)/1024/1024),2),'M') from information_schema.tables group by table_schema;
2. Match ''
LIKE '\\\%';
3. Execute SQL file
source sql脚本绝对路径;
4.SQL statement defines variables:
select @param1 from (select @param1:=0,@param2:='123',@param3:='456') t
5. Connect to MySQL client
mysql -uroot -p123 -h10.0.0.52 -P3306
6.LPAD function
LPAD(str,len,padstr)
Returns the string str, left-padded with the string padstr to the length of len characters. If str is greater than len, the return value is shortened to len characters.
7.STR_TO_DATE(str,format) function
The STR_TO_DATE(str,format) function converts the time format string (str) into a DATETIME type value according to the provided display format (format). For example:
SELECT STR_TO_DATE('2017-01-06 10:20:30','%Y-%m-%d %H:%i:%s') AS result;
8.DATE_FORMAT(date,format) function
The DATE_FORMAT(date,format) function converts the date in the database into the corresponding string format.
9. Solve the Mysql group_concat length limit
SET GLOBAL group_concat_max_len=102400;
SET SESSION group_concat_max_len=102400;
验证：
SELECT @@global.group_concat_max_len; show variables like “group_concat_max_len”;
10. View master-slave synchronization
select * from performance_schema.replication_group_members;
11. Export all databases without data
mysqldump -u root -pmetadata@Tbds.com --no-data --all-databases > alldb.sql
12. Execute sql file (outside the client)
mysql -uroot -pmetadata@Tbds.com -h172.16.122.44 -e "set global read_only=off;source /root/alldb.sql"
13. Export specified libraries and data
mysqldump -h10.224.192.116 -uroot -pz3wgFBXc50KLV6U# --single-transaction hivemetastore > hivemetastore-source.sql
14. Modify the library name
rename table metastore.tab_name to hivemetastore.tab_name
15. Modify table name
alter table bucketing_cols rename to BUCKETING_COLS;
16. Check the number of database connections
show variables like '%max_connections%';
show status like 'Threads%';
17. Vertical display output
select * from inlong_offline_task_run \G;
18. Turn off foreign key checking
SET FOREIGN_KEY_CHECKS = 0;