Question

我对SQL有初学者知识，我想知道这是否可以在SQL中使用。

SQL查询1＆gt;＆gt;

select distinct(id) as active_pod from schema_naming

查询1输出＆gt;＆gt;

active_pod
DB_1
DB_2
... 
DB_20

SQL查询2＆gt;＆gt;

select * from DB_1.mapping UNION
select * from DB_2.mapping UNION
....
select * from DB_20.mapping UNION

由于我对SQL的了解有限，我现在首先运行＃1查询，每次更改查询2中的DB_1，DB2，... DB_20并运行＃2。

但是，我想知道在一个查询中是否有这种方法，所以我不必手动更改＃2查询中的DB编号，也不必每行合并。

像这样......（但不知道如何处理工会）

select * from {
select distinct id from schema_naming}.user_map

如果有人能够阐明这一点，那就太好了。（我试图在Oracle SQL上执行此操作）

提前谢谢。

Answer 1

你想要得到这样的东西吗？

SELECT 'SELECT * FROM ' || active_pod  || '.' || 'Mapping UNION'
FROM
(
select distinct(id) as active_pod from schema_naming
) as DT;

Answer 2

这绝对是一个黑客，但它可能会让你的生活更轻松，直到提出更好的解决方案。基本上使用查询来生成第二个查询，只需要手动编辑就可以删除最后一行中不必要的UNION。

SELECT 'SELECT * FROM ' || ACTIVE_POD || '.MAPPING UNION' AS QUERY
FROM SCHEMA_NAMING

结果：

SELECT * FROM DB_1.MAPPING UNION
SELECT * FROM DB_2.MAPPING UNION
SELECT * FROM DB_3.MAPPING UNION
SELECT * FROM DB_4.MAPPING UNION
SELECT * FROM DB_5.MAPPING UNION
SELECT * FROM DB_6.MAPPING UNION
SELECT * FROM DB_7.MAPPING UNION
SELECT * FROM DB_8.MAPPING UNION
SELECT * FROM DB_9.MAPPING UNION
SELECT * FROM DB_10.MAPPING UNION
SELECT * FROM DB_11.MAPPING UNION
SELECT * FROM DB_12.MAPPING UNION
SELECT * FROM DB_13.MAPPING UNION
SELECT * FROM DB_14.MAPPING UNION
SELECT * FROM DB_15.MAPPING UNION
SELECT * FROM DB_16.MAPPING UNION
SELECT * FROM DB_17.MAPPING UNION
SELECT * FROM DB_18.MAPPING UNION
SELECT * FROM DB_19.MAPPING UNION
SELECT * FROM DB_20.MAPPING UNION

Answer 3

或者，使用PL / SQL块：

BEGIN
For i in (SELECT 'SELECT * FROM ' || ACTIVE_POD || '.MAPPING UNION' AS QUERY
FROM SCHEMA_NAMING) loop
dbms_output.put_line(i.query);
end loop;
END

您的查询将显示在IDE的输出窗口中。

SQL连接for Loop？

3 个答案: