sql - SQL 模式和值

Question

我有一个我想做的选择声明。我要选择

SELECT COLUMN_NAME AS FieldName FROM   
INFORMATION_SCHEMA.COLUMNS 
WHERE TABLE_NAME = 'table1'

但是我想创建另一个名为 Value 的列，它是 table1 中的特定行，所以我有列名的行和相应的单个值。关于如何解决这个问题的任何想法？

Answer 1

以下查询为每列生成一个值（最小值）：

    SELECT '''select '+COLUMN_NAME+''' AS FieldName, (select cast(MIN('+COLUMN_NAME+') as varchar(8000)) from '+const.tablename+')'
    FROM INFORMATION_SCHEMA.COLUMNS c cross join
         (select 'AllCurveNames' as tablename) const
    WHERE c.TABLE_NAME = const.tablename

但是，这会为每一行生成一个单独的查询。要将它们组合在一起，您需要一个字符串聚合连接。这就是您在 SQL Server 中的操作方式：

    declare @sql varchar(max);

    SELECT @sql = (select 'select '''+COLUMN_NAME+''' AS FieldName, (select cast(MIN('+COLUMN_NAME+') as varchar(8000)) from '+const.tablename + ') union all '
                   FROM INFORMATION_SCHEMA.COLUMNS c cross join
                        (select WHATEVER as tablename) const
                   WHERE c.TABLE_NAME = const.tablename
                   for xml path('')
                  );
    select @sql = LEFT(@sql, len(@sql) - 9);
    exec(@sql);

Answer 2

使用交叉连接，如果您只是从两个没有连接的表中选择（即from t1, t2），则这是隐式的：

SELECT COLUMN_NAME AS FieldName,
       Table1.MyField
FROM
    INFORMATION_SCHEMA.COLUMNS, Table1
WHERE
    TABLE_NAME = 'table1'
AND
    MyTable.ID = 123

Answer 3

我实际上想出了一个疯狂的解决方案，但它确实有效：

declare @tbl_name as varchar(255)
declare @field as varchar(255)
declare @val as varchar(255)
declare @SQL as nvarchar(4000)

create table #tbl ( [FieldName][varchar](255), [FieldVal][varchar](255))

set @tbl_name = 'table1'

DECLARE mah_cursor CURSOR FAST_FORWARD 
FOR 
SELECT COLUMN_NAME FROM  
INFORMATION_SCHEMA.COLUMNS 
WHERE TABLE_NAME = @tbl_name

OPEN mah_cursor

FETCH NEXT FROM mah_cursor INTO @field 

WHILE @@FETCH_STATUS = 0
BEGIN



set @SQL = 'set @val = (Select top 1 ' + @field + ' from ' + @tbl_name + ')' 
print @SQL


exec sp_executesql @query = @SQL, @params = N'@val varchar(255) OUTPUT', @val = @val      OUTPUT

 insert into #tbl ([FieldName],[FieldVal] ) values (@field, @val)

 FETCH NEXT FROM mah_cursor INTO @field
 END

CLOSE mah_cursor 
DEALLOCATE mah_cursor 

select * from #tbl

drop table #tbl

它遍历每个值并添加它。Fast_Forward 功能优化查询以获得高性能