mysql - if 和 col_length 语法

Question

声明:

if col_length('memes', 'rating_test') is null 
    begin 
    alter table `memes` add column `rating_test` varchar(36) 
    end  

错误消息:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'if col_length('memes', 'rating_test') is null begin alter table `memes` add colu' at line 1

为什么会产生上述错误消息？

Answer 1

你的语法不正确，使用这个语法它应该可以工作。

    If Exists (Select 1 from INFORMATION_SCHEMA.TABLES Where  Table_Name = N'YourTableName')
BEGIN
    If(COL_LENGTH('[TableName]','ColumnName') is NULL)
    BEGIN
        Alter Table [TableName]
        Add ColumnName DataType(Size) NULL
    END
END
GO