Select 列名称基于两个单独的 table 和数据库中的条件

Question

我在两个单独的数据库中有相同的 table（架构可能不同，所以我使用 'intersect'）：

来自数据库 1 的 MyTable
来自数据库 2 的 MyTable

当当前列的行在 Database1 中具有 NULL 值而在 Database2 中具有 NOT NULL 时，我想获取列名，如果可能的话还包括数据。

查询可以如下所示：

SELECT (
    SELECT COLUMN_NAME FROM Database1.INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='MyTable' AND TABLE_SCHEMA='dbo'
    INTERSECT
    SELECT COLUMN_NAME FROM Database2.INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='MyTable' AND TABLE_SCHEMA='dbo'
) /* +data ? */
FROM Database1.dbo.MyTable AS MyTable1 INNER JOIN
Database2.dbo.MyTable AS MyTable2 ON MyTable1.id = MyTable2.id
WHERE MyTable1.COLUMN_NAME IS NULL AND MyTable2.COLUMN_NAME IS NOT NULL
OR MyTable2.COLUMN_NAME IS NULL AND MyTable1.COLUMN_NAME IS NOT NULL

但这显然是错误的。

Answer 1

为此你需要动态 SQL，它不会很漂亮。

DECLARE @sql     nvarchar(max) = N'SELECT t1.id',
        @sel     nvarchar(max) = N'', 
        @clauses nvarchar(max) = N'';
  
;WITH src(col, name) AS
(
      SELECT QUOTENAME(c.name), c.name 
        FROM Database1.sys.columns AS c
        INNER JOIN Database1.sys.tables AS t
        ON c.[object_id] = t.[object_id]
        WHERE t.name = N'MyTable' AND t.schema_id = 1
      INTERSECT 
      SELECT QUOTENAME(c.name), c.name 
        FROM Database2.sys.columns AS c
        INNER JOIN Database2.sys.tables AS t
        ON c.[object_id] = t.[object_id]
        WHERE t.name = N'MyTable' AND t.schema_id = 1
),
clauses(clause, sel) AS
(
  SELECT clause = char(13) + char(10)
      + N'  OR (   (t1.' + col + N' IS NULL AND t2.' + col + N' IS NOT NULL)'
      + char(13) + char(10) 
      + '       OR (t1.' + col + N' IS NOT NULL AND t2.' + col + N' IS NULL))',
    sel = N',' + char(13) + char(10) 
      + N'  t1_' + name + N' = t1.' + col 
      + N', t2_' + name + N' = t2.' + col
  FROM src
  WHERE name <> N'id'
)
SELECT @sel += sel, @clauses += clause FROM clauses;
  
SELECT @sql += @sel 
   + char(13) + char(10) + N' FROM Database1.dbo.MyTable AS t1'
   + char(13) + char(10) + N' INNER JOIN Database2.dbo.MyTable AS t2'
   + char(13) + char(10) + N' ON t1.id = t2.id AND (1 = 2' + @clauses + N');';
  
SELECT @sql;
--EXEC sys.sp_executesql @sql;

输出（假设 MyTable 具有公共列 id、x 和 y）：

SELECT t1.id,
  t1_x = t1.[x], t2_x = t2.[x],
  t1_y = t1.[y], t2_y = t2.[y]
 FROM Database1.dbo.MyTable AS t1
 INNER JOIN Database2.dbo.MyTable AS t2
 ON t1.id = t2.id AND (1 = 2
  OR (   (t1.[x] IS NULL AND t2.[x] IS NOT NULL)
       OR (t1.[x] IS NOT NULL AND t2.[x] IS NULL))
  OR (   (t1.[y] IS NULL AND t2.[y] IS NOT NULL)
       OR (t1.[y] IS NOT NULL AND t2.[y] IS NULL)));

Select 列名称基于两个单独的 table 和数据库中的条件

Select column names based on condition in two separate table and database

sql

database

sql-server

sql-server-2008