SQL to return first two columns of a table

Is there any SQL lingo to return JUST the first two columns of a table WITHOUT knowing the fie开发者_Go百科ld names?

Something like

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

Or do I have to go the long way around and find out the column names first? How would I do that?

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You have to get the column names first. Most platforms support this:

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

---

There it´s

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)

---

A dynamic query using for xml path will also do the job:

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')

---

I wrote a stored procedure a while back to do this exact job. Even though in relational theory there is no technical column order SSMS is not completely relational. The system stores the order in which the columns were inserted and assigns an ID to them. This order is followed using the typical SELECT * statement which is why your SELECT statements appear to return the same order each time. In practice its never a good idea to SELECT * with anything as it doesn't lock the result order in terms of columns or rows. That said I think people get so stuck on 'you shouldn't do this' that they don't write scripts that actually can do it. Fact is there is predictable system behavior so why not use it if the task isn't super important.

This SPROC of course has caveats and is written in T-SQL but if your looking to just return all of the values with the same behavior of SELECT * then this should do the job pretty easy for you. Put in your table name, the amount of columns, and hit F5. It returns them in order from left to right the same as you'd be expecting. I limited it to only 5 columns but you can edit the logic if you need any more. Takes both temp and permanent tables.

EXEC OnlySomeColumns '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

---

SQL doesn't understand the order of columns. You need to know the column names to get them.

You can look into querying the information_schema to get the column names. For example:

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

---

You can query the sysobject of the table to find out the first two column then dynamically generate the SQL statement you need.

---

If you want a permant object that you can query over and over again make a view for each table that only returns the first 2 columns. You can name the columns Column1 and Column2 or use the existing names.

If you want to return the first two columns from any table without any preprocessing steps create a stored procedure that queries the system information and executes a dynamic query that return the first two columns from the table.

---

Or do I have to go the long way around and find out the column names first? How would I do that?

It's pretty easy to do manually.
Just run this first

select * from tbl where 1=0

This statement works on all major DBMS without needing any system catalogs. That gives you all the column names, then all you need to do is type the first two

select colname1, colnum2 from tbl