查看information_schema.tables：
DESC information_schema.TABLES
TABLE_SCHEMA ---->库名
TABLE_NAME ---->表名
ENGINE ---->引擎
TABLE_ROWS ---->表的行数
AVG_ROW_LENGTH ---->表中行的平均行（字节）
INDEX_LENGTH ---->索引的占用空间大小（字节）
使用案例：
查询整个数据库中所有库和所对应的表信息：
SELECT table_schema,GROUP_CONCAT(table_name)
FROM information_schema.tables
GROUP BY table_schema;
统计所有库下的表个数：
SELECT table_schema,COUNT(table_name)
FROM information_schema.TABLES
GROUP BY table_schema
查询所有innodb引擎的表及所在的库：
SELECT table_schema,table_name,ENGINE FROM information_schema.`TABLES`
WHERE ENGINE='innodb';
统计world数据库下每张表的磁盘空间占用：
SELECT table_name,CONCAT((TABLE_ROWS*AVG_ROW_LENGTH+INDEX_LENGTH)/1024," KB") AS size_KB
FROM information_schema.tables WHERE TABLE_SCHEMA='world';
统计所有数据库的总的磁盘空间占用：
SELECT
TABLE_SCHEMA,
CONCAT(SUM(TABLE_ROWS*AVG_ROW_LENGTH+INDEX_LENGTH)/1024," KB") AS Total_KB
FROM information_schema.tables
GROUP BY table_schema;
mysql -uroot -p123 -e "SELECT TABLE_SCHEMA,CONCAT(SUM(TABLE_ROWS*AVG_ROW_LENGTH+INDEX_LENGTH)/1024,' KB') AS Total_KB FROM information_schema.tables GROUP BY table_schema;"
生成整个数据库下的所有表的单独备份语句：
# 模板语句：
mysqldump -uroot -p123 world city >/tmp/world_city.sql
# 实例1：
SELECT CONCAT("mysqldump -uroot -p123 ",table_schema," ",table_name," >/tmp/",table_schema,"_",table_name,".sql" )
FROM information_schema.tables
WHERE table_schema NOT IN('information_schema','performance_schema','sys')
INTO OUTFILE '/tmp/bak.sh' ;
# PS：字符串拼接函数
CONCAT("mysqldump -uroot -p123 ",table_schema," ",table_name," >/tmp/",table_schema,"_",table_name,".sql" )
107张表，都需要执行以下2条语句：
# 107张表，需要执行的2条语句：
ALTER TABLE world.city DISCARD TABLESPACE;
ALTER TABLE world.city IMPORT TABLESPACE;
# 实现第一条语句：
SELECT CONCAT("alter table ",table_schema,".",table_name," discard tablespace")
FROM information_schema.tables
WHERE table_schema='world'
INTO OUTFILE '/tmp/dis.sql';
