许多数据库的元数据都是存储在mysql中的，例如hive、startrockes，因此可以通过mysql中的“information_schema.TABLES”表来查询对应数据库或对应数据表的具体信息。

1、查询各个数据库中的数据条数和数据大小

SELECT
	TABLE_SCHEMA AS '数据库',
	sum( table_rows ) AS '记录数',
	sum(
	TRUNCATE ( data_length / 1024 / 1024, 2 )) AS '数据容量(MB)',
	sum(
	TRUNCATE ( index_length / 1024 / 1024, 2 )) AS '索引容量(MB)'
FROM
	information_schema.TABLES
GROUP BY
	TABLE_SCHEMA
ORDER BY
	sum( data_length ) DESC,
	sum( index_length ) DESC;

2、查询各个数据表中的数据条数和数据大小

SELECT
	table_schema AS '数据库',
	table_name AS '表名',
	table_rows AS '记录数',
	TRUNCATE ( data_length / 1024 / 1024, 2 ) AS '数据容量(MB)',
	TRUNCATE ( index_length / 1024 / 1024, 2 ) AS '索引容量(MB)' 
FROM
	information_schema.TABLES 
ORDER BY
	data_length DESC,
	index_length DESC;

3、查看指定数据库容量大小

SELECT
	table_schema AS '数据库',
	sum( table_rows ) AS '记录数',
	sum(
	TRUNCATE ( data_length / 1024 / 1024, 2 )) AS '数据容量(MB)',
	sum(
	TRUNCATE ( index_length / 1024 / 1024, 2 )) AS '索引容量(MB)' 
FROM
	information_schema.TABLES 
WHERE
	table_schema = 'test';

4、查看指定数据库各表容量大小

SELECT
	table_schema AS '数据库',
	table_name AS '表名',
	table_rows AS '记录数',
	TRUNCATE ( data_length / 1024 / 1024, 2 ) AS '数据容量(MB)',
	TRUNCATE ( index_length / 1024 / 1024, 2 ) AS '索引容量(MB)' 
FROM
	information_schema.TABLES 
WHERE
	table_schema = 'test' 
ORDER BY
	data_length DESC,
	index_length DESC;

5、查看指定数据库各表的列数

SELECT TABLE_NAME, COUNT(*) AS COLUMN_COUNT
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'test'
GROUP BY TABLE_NAME;