如何从不同的数据库访问 table 的行

Question

我正在创建一个存储过程，使用@dbname、@schemaname 和@tablename 作为参数，objective 计算 table 的每一列中的空值, 但我无法从不同的数据库访问数据。

我正在尝试这样的事情

create or alter proc testnulls(
       @dbname     sysname = N'master', 
      @schemaname sysname = N'dbo', 
      @tablename  sysname = N'spt_values'
      )
as

DECLARE @sql nvarchar(max) 

select @sql = @sql + '
   sum(case when [' + c.name + '] is null then 1 else 0 end) as [' + c.name + '_NULLS]'
fROM sys.columns AS c 
INNER JOIN sys.all_objects AS t
ON c.[object_id] = t.[object_id]
INNER JOIN sys.schemas AS s
ON t.[schema_id] = s.[schema_id]
where t.name = @tablename
and s.name=@schemaname

set @sql = @sql + ' from '+ QUOTENAME(@dbname)+  N'.'+ QUOTENAME(@schemaname)+ N'.' + QUOTENAME(@tablename)
select @sql

Answer 1

只能说，不好看；动态动态 SQL 永远不会。不会撒谎，我真的不想解释这是在做什么，一团糟。如果需要，我建议使用我放入其中的 PRINT 语句来调试它。

CREATE OR ALTER PROC dbo.testnulls @dbname     sysname = N'master', 
                                   @schemaname sysname = N'dbo', 
                                   @tablename  sysname = N'spt_values' AS
BEGIN 

    --DECLARE @dbname     sysname = N'master', 
    --        @schemaname sysname = N'dbo', 
    --        @tablename  sysname = N'spt_values';

    DECLARE @SQL nvarchar(MAX), @DSQL nvarchar(MAX);

    SET @SQL = N'SET @DSQL = N''SELECT '' + STUFF((SELECT N'', COUNT('' + QUOTENAME(c.[name]) + N'') AS '' + QUOTENAME(CONCAT(c.[name],N''_NULL''))
                                                   FROM ' + QUOTENAME(@dbname) + N'.sys.schemas s
                                                         JOIN ' + QUOTENAME(@dbname) + N'.sys.all_objects o ON s.schema_id = o.schema_id
                                                         JOIN ' + QUOTENAME(@dbname) + N'.sys.columns c ON o.object_id = c.object_id
                                                   WHERE s.[name] = @schemaname
                                                     AND o.[name] = @tablename
                                                   FOR XML PATH(N''''),TYPE).value(''(./text())[1]'',''nvarchar(MAX)''),1,2,N'''') + 
                             N''FROM ' + QUOTENAME(@dbname) + N'.' + QUOTENAME(@schemaname) + N'.' + QUOTENAME(@tablename) + N';''
               EXEC sys.sp_executesql @DSQL, N''@schemaname sysname, @tablename sysname'', @schemaname, @tablename;';

    EXEC sys.sp_executesql @SQL, N'@schemaname sysname, @tablename sysname, @DSQL nvarchar(MAX) OUTPUT', @schemaname, @tablename, @DSQL OUT;

    PRINT @DSQL;
    PRINT @SQL;
END;

如何从不同的数据库访问 table 的行

How to access rows of a table from a different database

sql

sql-server

ssms