T-SQL检查存储过程中是否存在不存在的列

Question

I have a problem with IF NOT EXISTS statement. I have used the following code inside of using a stored procedure:

IF NOT EXISTS(SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS
                         WHERE TABLE_NAME = 'tableName'
                         AND COLUMN_NAME = @fieldName
                         AND TABLE_SCHEMA = 'dbo')   
BEGIN  
       DECLARE @paramDefinitions NVARCHAR(1000)

    SET @paramDefinitions=
     '@dataType nvarchar(100) OUTPUT'
        SET @typeQuery = 'SELECT @dataType =
                  CASE 
                  WHEN s.name = ''nvarchar'' THEN ''nvarchar('' + CAST(c.max_length AS varchar(4)) + '')'' 
                      WHEN s.name = ''varchar'' THEN ''varchar('' + CAST(c.max_length AS varchar(4)) + '')''
                      WHEN s.name = ''char'' THEN ''char('' + CAST(c.max_length AS varchar(4)) + '')''
              WHEN s.name = ''nchar'' THEN ''nchar('' + CAST(c.max_length AS varchar(4)) + '')''
             ELSE s.name 
              END                 
            FROM sys.views t JOIN sys.columns c ON t.object_id = c.object_id 
                              JOIN sys.types s ON c.user_type_id = s.user_type_id 
            WHERE t.name = ''tablename'' AND c.name =' + @tmpField

            EXEC sp_executesql @typeQuery, @paramDefinitions, @dataType OUTPUT

            SET @updateTable = 'Alter table dbo.tablename add ' + @field +' '+ @dataType 
            print @updateTable

        EXEC sp_executesql @updateTable  
END

If I now start the SP it tries to recreate the already existing columns, but it will also create any new column. If I change it to IF EXISTS it won't do anything.

If I run the select statement by itself I get a 1 as a result if the column exists and nothing if it doesn't. Where is my mistake? Is it not possible to use IF NOT EXISTS for this purpose?

Answer 1

If I want to check if a table contains some column, I use COLUMNPROPERTY :

IF COLUMNPROPERTY(object_id('[dbo].[TABLE]'), 'COLUMN_NAME', 'AllowsNull') is NULL
BEGIN
SELECT 'The column does not exists'
END