Question

我想从数据库的每个表中选择*。我该怎么办？

我尝试了以下脚本：

SELECT * 
  FROM 
     ( SELECT TABLE_NAME 
         FROM INFORMATION_SCHEMA.TABLES 
         WHERE TABLE_CATALOG = 'databasename'
     )

SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_CATALOG = 'databasename'已经返回了数据库的每个表名，但是如何从“列表”中选择所有内容？

Answer 1

在游标非常有用的极少数情况下，因为您需要迭代information_schema表，构建准备好的语句并执行它（请注意，一次只能向动态sql提交1条语句。

drop procedure if exists p;

delimiter $$

CREATE  PROCEDURE p()

begin 
     declare vtable_name varchar(100);
     declare done int;
    declare c7 cursor for SELECT   TABLE_NAME 
         FROM INFORMATION_SCHEMA.TABLES 
         WHERE TABLE_schema = 'sandbox' and table_type = 'base table' and table_name in ('t', 't1');

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    open c7;
    cursorloop:loop
        fetch c7 into vtable_name;
        if done = true then  
        leave cursorloop;
        end if;  
        set @sql = concat('select * from ', vtable_name,';');
        select @sql;
        prepare sqlstmt from @sql;
        execute sqlstmt;
        deallocate prepare sqlstmt; 
     end loop cursorloop;
    close c7;
 end $$

 delimiter ;

 call p();

请注意，出于说明目的，我限制了光标的选择，并限制了返回基表的内容（您可能会或可能不希望包含视图）

MariaDB [sandbox]> call p();
+------------------+
| @sql             |
+------------------+
| select * from t; |
+------------------+
1 row in set (0.00 sec)

+------+------+-------+
| id   | user | value |
+------+------+-------+
|    1 | A    | Cool  |
|    2 | A    | Cool  |
|    3 | A    | Cool  |
|    2 | A    | Warm  |
|    3 | A    | Warm  |
|    4 | B    | Cool  |
|    5 | C    | Cool  |
|    5 | C    | Warm  |
+------+------+-------+
8 rows in set (0.00 sec)

+-------------------+
| @sql              |
+-------------------+
| select * from t1; |
+-------------------+
1 row in set (0.04 sec)

+------+-------+
| sku  | stock |
+------+-------+
|    1 |     5 |
|    2 |     5 |
+------+-------+
2 rows in set (0.04 sec)

特别注意内置的sql语句。

从多个表名中选择*

1 个答案: