Table name as variable

Question

I am trying to execute this query:

declare @tablename varchar(50)
set @tablename = 'test'
select * from @tablename

This produces the following error:

Msg 1087, Level 16, State 1, Line 5

Must declare the table variable "@tablename".

What's the right way to have table name populated dynamically?

Answer 1

Declare @fs_e int, @C_Tables CURSOR, @Table varchar(50)

SET @C_Tables = CURSOR FOR
        select name from sysobjects where OBJECTPROPERTY(id, N'IsUserTable') = 1 AND name like 'TR_%'
OPEN @C_Tables
FETCH @C_Tables INTO @Table
    SELECT @fs_e = sdec.fetch_Status FROM sys.dm_exec_cursors(0) as sdec where sdec.name = '@C_Tables'

WHILE ( @fs_e <> -1)
    BEGIN
        exec('Select * from '+ @Table)
        FETCH @C_Tables INTO @Table
        SELECT @fs_e = sdec.fetch_Status FROM sys.dm_exec_cursors(0) as sdec where sdec.name = '@C_Tables'
    END

Answer 2

Also, You can use this...

DECLARE @SeqID varchar(150);
DECLARE @TableName varchar(150);  
SET @TableName = (Select TableName from Table);
SET @SeqID = 'SELECT NEXT VALUE FOR '+ @TableName + '_Data'
exec (@SeqID)

Answer 3

Change your last statement to this:

EXEC('SELECT * FROM ' + @tablename)

This is how I do mine in a Stored Procedure. The first block will declare the variable, and set the table name based on the current year and month name, in this case TEST_2012OCTOBER. I then check if it exists in the DB already, and remove if it does. Then the next block will use a SELECT INTO Statement to create the table and populate it with records from another table with parameters.

--DECLARE TABLE NAME VARIABLE DYNAMICALLY
DECLARE @table_name varchar(max)
SET @table_name = 
    (SELECT 'TEST_'
            + DATENAME(YEAR,GETDATE())
            + UPPER(DATENAME(MONTH,GETDATE())) )

--DROP THE TABLE IF IT ALREADY EXISTS
IF EXISTS(SELECT name 
          FROM sysobjects 
          WHERE name = @table_name AND xtype = 'U')

BEGIN
    EXEC('drop table ' +  @table_name)
END

--CREATES TABLE FROM DYNAMIC VARIABLE AND INSERTS ROWS FROM ANOTHER TABLE
EXEC('SELECT * INTO ' + @table_name + ' FROM dbo.MASTER WHERE STATUS_CD = ''A''')

Answer 4

Table names and column names need to be static, if the query is static. For dynamic table or column names, you should generate the full SQL dynamically, and use sp_executesql to execute it.

More details here: The curse and blessings of dynamic SQL

Answer 5

You can't use a table name for a variable, you'd have to do this instead:

DECLARE @sqlCommand varchar(1000)
SET @sqlCommand = 'SELECT * from yourtable'
EXEC (@sqlCommand)

Answer 6

Use sp_executesql to execute any SQL, e.g.

DECLARE @tbl    sysname,
        @sql    nvarchar(4000),
        @params nvarchar(4000),
        @count  int

DECLARE tblcur CURSOR STATIC LOCAL FOR
   SELECT object_name(id) FROM syscolumns WHERE name = 'LastUpdated'
   ORDER  BY 1
OPEN tblcur

WHILE 1 = 1
BEGIN
   FETCH tblcur INTO @tbl
   IF @@fetch_status <> 0
      BREAK

   SELECT @sql =
   N' SELECT @cnt = COUNT(*) FROM dbo.' + quotename(@tbl) +
   N' WHERE LastUpdated BETWEEN @fromdate AND ' +
   N'                           coalesce(@todate, ''99991231'')'
   SELECT @params = N'@fromdate datetime, ' +
                    N'@todate   datetime = NULL, ' +
                    N'@cnt      int      OUTPUT'
   EXEC sp_executesql @sql, @params, '20060101', @cnt = @count OUTPUT

   PRINT @tbl + ': ' + convert(varchar(10), @count) + ' modified rows.'
END

DEALLOCATE tblcur