Add a column to a table, if it does not already exist

2018-07-03 21:23:43

I want to write a query for MS SQL Server that adds a column into a table. But I don't want any error display, when I run/execute the following query.

I am using this sort of query to add a table ...

IF EXISTS (
       SELECT *
       FROM   sys.objects
       WHERE  OBJECT_ID = OBJECT_ID(N'[dbo].[Person]')
              AND TYPE IN (N'U')
   )

But I don't know how to write this query for a column.

您可以通过使用sys.columns表io sys.objects来使用类似的结构。

IF NOT EXISTS (
  SELECT * 
  FROM   sys.columns 
  WHERE  object_id = OBJECT_ID(N'[dbo].[Person]') 
         AND name = 'ColumnName'
)

IF COL_LENGTH('table_name', 'column_name') IS NULL
BEGIN
    ALTER TABLE table_name
    ADD [column_name] INT
END

Another alternative. I prefer this approach because it is less writing but the two accomplish the same thing.

IF COLUMNPROPERTY(OBJECT_ID('dbo.Person'), 'ColumnName', 'ColumnId') IS NULL
BEGIN
    ALTER TABLE Person 
    ADD ColumnName VARCHAR(MAX) NOT NULL
END

I also noticed yours is looking for where table does exist that is obviously just this

 if COLUMNPROPERTY( OBJECT_ID('dbo.Person'),'ColumnName','ColumnId') is not null

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