SQLServer常用语句
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+ 检测某个列是否已经存在(在向表中添加一列之前执行):

    .. code-block :: sql
        
        IF NOT EXISTS ( SELECT  *
                    FROM    sys.columns
                    WHERE   object_id = OBJECT_ID('table_name')
                            AND name = 'column_name' )

+ 向表中添加一列并连接到另一张表的外键连接:
    
    .. code-block :: sql

        ALTER TABLE [dbo].[TableA] ADD [ColumnName] [DataType] NULL 
        GO
        ALTER TABLE [dbo].[TableA]  WITH CHECK ADD  CONSTRAINT [fk_TableA_ColumnName] FOREIGN KEY([ColumnName])
        REFERENCES [dbo].[TableB] ([id])
        GO
        ALTER TABLE [dbo].[TableA] CHECK CONSTRAINT [fk_TableA_ColumnName]