SQL返回表的前两列

是否存在只返回表的前两列而不知道字段名的SQL术语

差不多

SELECT Column(1), Column(2) FROM Table_Name

---

还是我必须走很长的路，先找出列名？我该怎么做呢？

SQL不了解列的顺序。您需要知道列名才能获得它们

您可以查询信息模式以获取列名。例如：

SELECT column_name
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE table_name = 'tbl_name'
  ORDER BY ordinal_position
  LIMIT 2;

---

你必须先得到列名。大多数平台支持这一点：

select column_name,ordinal_position
  from information_schema.columns
 where table_schema = ...
   and table_name = ...
   and ordinal_position <= 2

---

您可以查询表的sysobject以找出前两列，然后动态生成所需的SQL语句

如果您想要一个可以反复查询的永久对象，请为每个表创建一个仅返回前2列的视图。可以将列命名为Column1和Column2，也可以使用现有名称

如果要在不执行任何预处理步骤的情况下从任何表返回前两列，请创建一个查询系统信息的存储过程，并执行从表返回前两列的动态查询

还是我必须走很长的路，先找出列名？我该怎么做

手工操作很容易。 先运行这个

select * from tbl where 1=0

此语句适用于所有主要DBMS，无需任何系统目录。 这将提供所有列名，然后只需键入前两个

select colname1, colnum2 from tbl

在那里

declare @select varchar(max)
set @select = 'select '

select @select=@select+COLUMN_NAME+','
from information_schema.columns
where table_name = 'TABLE' and ordinal_position <= 2

set @select=LEFT(@select,LEN(@select)-1)+' from TABLE'
exec(@select)

---

不久前，我编写了一个存储过程来完成这项工作。即使在关系理论中没有技术列顺序，SSMS也不是完全相关的。系统存储列的插入顺序，并为其分配ID。使用典型的SELECT*语句遵循此顺序，这就是SELECT语句每次返回相同顺序的原因。实际上，用任何东西选择*都不是一个好主意，因为它不会锁定列或行的结果顺序。也就是说，我认为人们太执着于“你不应该这样做”，以至于他们无法编写真正能够做到这一点的脚本。事实上，存在可预测的系统行为，所以如果任务不是非常重要，为什么不使用它呢

这个存储过程当然有一些警告，并且是用T-SQL编写的，但是如果您希望只返回所有具有相同SELECT*行为的值，那么这对您来说应该非常容易。输入表名、列数，然后按F5键。它按从左到右的顺序返回它们，与您预期的相同。我将其限制为仅5列，但如果需要，您可以编辑逻辑。接受临时表和永久表

仅执行部分列“MyTable”，3

/*------------------------------------------------------------------------------------------------------------------

    Document Title: The Unknown SELECT SPROC.sql

    Created By: CR
    Date: 4.28.2013

    Purpose: Returns all results from temp or permanent table when not knowing the column names

    SPROC Input Example: EXEC OnlySomeColumns 'MyTable', 3

--------------------------------------------------------------------------------------------------------------------*/

    IF OBJECT_ID ('OnlySomeColumns', 'P') IS NOT NULL
    DROP PROCEDURE OnlySomeColumns;

    GO

        CREATE PROCEDURE OnlySomeColumns 
                @TableName      VARCHAR (1000),
                @TotalColumns   INT

    AS

        DECLARE @Column1        VARCHAR (1000), 
                @Column2        VARCHAR (1000), 
                @Column3        VARCHAR (1000), 
                @Column4        VARCHAR (1000), 
                @Column5        VARCHAR (1000), 
                @SQL            VARCHAR (1000),
                @TempTable      VARCHAR (1000),
                @PermanentTable VARCHAR (1000),
                @ColumnNamesAll VARCHAR (1000)

        --First determine if this is a temp table or permanent table
        IF @TableName     LIKE '%#%' BEGIN SET @TempTable      = @TableName END --If a temporary table
        IF @TableName NOT LIKE '%#%' BEGIN SET @PermanentTable = @TableName END --If a permanent column name

    SET NOCOUNT ON

        --Start with a few simple error checks
        IF ( @TempTable = 'NULL' AND @PermanentTable = 'NULL' )
            BEGIN
                RAISERROR ( 'ERROR: Please select a TempTable or Permanent Table.',16,1 ) 
            END

        IF ( @TempTable <> 'NULL' AND @PermanentTable <> 'NULL' )
            BEGIN
                RAISERROR ( 'ERROR: Only one table can be selected at a time. Please adjust your table selection.',16,1 ) 
            END

        IF ( @TotalColumns IS NULL )
            BEGIN
                RAISERROR ( 'ERROR: Please select a value for @TotalColumns.',16,1 ) 
            END

    --Temp table to gather the names of the columns
    IF Object_id('tempdb..#TempName') IS NOT NULL DROP TABLE #TempName
    CREATE TABLE #TempName ( ID INT, Name VARCHAR (1000) )

        --Select the column order from a temp table
        IF @TempTable <> 'NULL'
            BEGIN       
                --Verify the temp table exists
                IF NOT EXISTS ( SELECT  1 
                                FROM    tempdb.sys.columns
                                WHERE   object_id = object_id ('tempdb..' + @TempTable +'') )
                BEGIN 
                    RAISERROR ( 'ERROR: Your TempTable does not exist - Please select a valid TempTable.',16,1 ) 
                            RETURN 
                        END 

                SET @SQL = 'INSERT INTO #TempName
                            SELECT  column_id AS ID, Name 
                            FROM    tempdb.sys.columns
                            WHERE   object_id = object_id (''tempdb..' + @TempTable +''')
                            ORDER BY    column_id'
                EXEC (@SQL) 
            END

        --From a permanent table
        IF @PermanentTable <> 'NULL'
            BEGIN       
                --Verify the temp table exists
                IF NOT EXISTS ( SELECT  1
                                FROM    syscolumns
                                WHERE   id =  ( SELECT id 
                                                FROM sysobjects 
                                                WHERE Name = '' + @PermanentTable + '' ) ) 
                BEGIN 
                    RAISERROR ( 'ERROR: Your Table does not exist - Please select a valid Table.',16,1 ) 
                            RETURN 
                        END 

                SET @SQL = 'INSERT INTO #TempName
                            SELECT   colorder AS ID, Name
                            FROM     syscolumns
                            WHERE id = ( SELECT id 
                                         FROM sysobjects 
                                         WHERE Name = ''' + @PermanentTable + ''' )
                            ORDER BY colorder'
                EXEC (@SQL)
            END

        --Set the names of the columns
        IF @TotalColumns >= 1 BEGIN SET @Column1 = (SELECT Name FROM #TempName WHERE ID = 1) END
        IF @TotalColumns >= 2 BEGIN SET @Column2 = (SELECT Name FROM #TempName WHERE ID = 2) END
        IF @TotalColumns >= 3 BEGIN SET @Column3 = (SELECT Name FROM #TempName WHERE ID = 3) END
        IF @TotalColumns >= 4 BEGIN SET @Column4 = (SELECT Name FROM #TempName WHERE ID = 4) END
        IF @TotalColumns >= 5 BEGIN SET @Column5 = (SELECT Name FROM #TempName WHERE ID = 5) END

    --Create a select list of only the column names you want
    IF Object_id('tempdb..#FinalNames') IS NOT NULL DROP TABLE #FinalNames
    CREATE TABLE #FinalNames ( ID INT, Name VARCHAR (1000) )

            INSERT  #FinalNames
            SELECT  '1' AS ID, @Column1 AS Name UNION ALL
            SELECT  '2' AS ID, @Column2 AS Name UNION ALL
            SELECT  '3' AS ID, @Column3 AS Name UNION ALL
            SELECT  '4' AS ID, @Column4 AS Name UNION ALL
            SELECT  '5' AS ID, @Column5 AS Name

            --Comma Delimite the names to insert into a select statement. Bracket the names in case there are spaces 
            SELECT  @ColumnNamesAll = COALESCE(@ColumnNamesAll + '], [' ,'[') + Name
            FROM    #FinalNames
            WHERE   Name IS NOT NULL
            ORDER BY ID

            --Add an extra bracket at the end to complete the string
            SELECT  @ColumnNamesAll = @ColumnNamesAll + ']'

        --Tell the user if they selected to many columns
        IF ( @TotalColumns > 5 AND EXISTS (SELECT 1 FROM #FinalNames WHERE Name IS NOT NULL) )
            BEGIN
                SELECT 'This script has been designed for up to 5 columns' AS ERROR
                UNION ALL
                SELECT 'Only the first 5 columns have been selected' AS ERROR
            END

        IF Object_id('tempdb..#FinalNames') IS NOT NULL DROP TABLE ##OutputTable

        --Select results using only the Columns you wanted
        IF @TempTable <> 'NULL'
            BEGIN
                SET @SQL = 'SELECT  ' + @ColumnNamesAll + '
                            INTO    ##OutputTable
                            FROM     ' + @TempTable + ' 
                            ORDER BY 1'
                EXEC (@SQL)
            END

        IF @PermanentTable <> 'NULL'
            BEGIN
                SET @SQL = 'SELECT  ' + @ColumnNamesAll + '
                            INTO    ##OutputTable
                            FROM     ' + @PermanentTable + ' 
                            ORDER BY 1'
                EXEC (@SQL) 
            END

    SELECT  *
    FROM    ##OutputTable

    SET NOCOUNT OFF

使用for xml path的动态查询也将完成此任务：

declare @sql varchar(max)
set @sql = (SELECT top 2 COLUMN_NAME + ',' from information_schema.columns where table_name = 'YOUR_TABLE_NAME_HERE' order by ordinal_position for xml path(''))
set @sql = (SELECT replace(@sql +' ',', ',''))
exec('SELECT ' + @sql + ' from YOUR_TABLE_NAME_HERE')

---

请参阅：如果您不知道列名，为什么要查询表？SQL Server Express 2008的错误超出了2位的限制-我可能应该提到我使用的是什么。除了一个非常流行的数据库管理系统名为OracleIt外，它为您提供了前两列，因为顺序位置条件。只要换成小于。