mysql - 如何从每个数据库(MySQL)的 information_Schema 中获取 n 行

Question

我不是 DBA 或......但我只是对编写查询非常感兴趣，比如学习它的技巧......现在我问自己这个问题:

How can I get n rows from information_Schema from each of databases? (Without knowing the number of databases)

例如......我们有3个数据库((information_Schema，stack，overflow) 我们不知道。

我想从每个数据库中获取 20 个表。我该怎么做？

还有一件事......请不要给我程序。

Answer 1

您可以使用以下内容来实现您想要的:

set @schema_name='';
set @num=0;

select table_schema, table_name FROM (
select 
  table_schema, 
  table_name, 
  @num := if(@schema_name = table_schema, @num + 1, 1) as dummy_1,
  @schema_name := table_schema as dummy_2,
  @num as row_number
  from information_schema.tables 
  group by table_schema, table_name
  having row_number <= 20) A ;