Question

我有4个具有相似模式的数据库，我正在尝试创建一个查询，只返回仅存在于数据库1中的表，列对，而不存在于数据库2,3或4中。

目前，我可以通过以下查询返回数据库1和2之间的对称差异...

select table_name, column_name from (
        select table_name, column_name from [Database1].information_schema.columns
        union all
        select table_name, column_name from [Database2].information_schema.columns) as tmp
        group by table_name, column_name having count(*) = 1

但是，在尝试仅隔离数据库1中的那些列并在所有4个数据库中执行相同操作时，事情变得越来越复杂。这个查询最干净的解决方案是什么？

Answer 1

SELECT
     D1.table_name,
     D1.column_name
FROM
     Database1.information_schema.columns D1
LEFT OUTER JOIN Database2.information_schema.columns D2 ON
     D2.table_name = D1.table_name AND
     D2.column_name = D1.column_name
LEFT OUTER JOIN Database3.information_schema.columns D3 ON
     D3.table_name = D1.table_name AND
     D3.column_name = D1.column_name
LEFT OUTER JOIN Database4.information_schema.columns D4 ON
     D4.table_name = D1.table_name AND
     D4.column_name = D1.column_name
WHERE
     D2.table_name IS NULL AND
     D3.table_name IS NULL AND
     D4.table_name IS NULL

Answer 2

我可以在第一次拍摄时提出这个问题，这可能是一个良好的开端。这还没有经过测试，只是另一种选择：

select table_name, column_name from [Database1].information_schema.columns d1
where table_name || '+' || column_name
not in (select table_name || '+' || column_name from [Database2].information_schema.columns)

and table_name || '+' || column_name
not in (select table_name || '+' || column_name from [Database3].information_schema.columns)

and table_name || '+' || column_name
not in(select table_name || '+' || column_name from [Database4].information_schema.columns)

在SQL数据库中查找唯一的表/列组合

2 个答案: