What is the usage of substr function in database?

Usage of the substr function in the database: 1. [SUBSTR(str,pos,len)] intercepts len characters from the position starting from pos; 2. [SUBSTR(str,pos)] starts from the position of pos, Cut to the end.

Usage of substr function in database:

1, SUBSTR(str,pos,len): From the starting position of pos, intercept len ​​characters

substr(string ,1,3) ：取string左边第1位置起，3字长的字符串。

So the result is: str

substr(string, -1,3)：取string右边第1位置起，3字长的字符串。显然右边第一位置起往右不够3字长。

The result can only be: g

substr(string, -3,3)：取string右边第3位置起，3字长的字符串。

The result is: ing

2, SUBSTR(str,pos): The starting position of pos, intercepted until the end

substr(string ,4) : 从右第4位置截取到最后

The result is: ing

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