新增評論

評論有三種型別：

 # This comment continues to the end of line

-- This comment continues to the end of line

/* This is an in-line comment */ 

/*
This is a
multiple-line comment
*/

例：

SELECT * FROM t1; -- this is comment

CREATE TABLE stack(
    /*id_user int,
    username varchar(30),
    password varchar(30)
    */
    id int
);

-- 方法要求在註釋開始之前在 -- 之後跟一個空格，否則它將被解釋為命令並且通常會導致錯誤。

#This comment works
/*This comment works.*/
--This comment does not.