MySQL common functions

    Be careful ： The function in this article contains Chinese characters , Don't copy , Type it yourself .

1. Maximum ：max

2. Round function ：

    round（x）： Returns the closest parameter x The integer value . for example round（3.14） return 3.

    round（x,y）：x For input parameters ,y To reserve decimal places .y Keep to ten digits when it is negative , Bits are 0.round(123.23)

3. The average ：avg

4. The absolute value ：abs( Value data );

5. Substitution function ：replace（'abcdefg','abc','aaa'）; The string ’abcdefg‘ Medium abc Replace with ’aaa'.

6.right(str,length),left(str,length), Intercept the right / The string on the left .

    substring(str,pos) From pos Start intercepting a string , Until the end

    substring（str,pos,length） From pos Start intercepting a string , Intercept length Characters .（pos When it's negative , It's the last to start intercepting ）.

7. String connection ：concat('sss','aaa') take sss Same as aaa Connect . There are null When to return to null.

                    concat_ws（‘,’,‘aaa’,'sss'）. The first string is the delimiter , The result is ‘aaa,sss’.

8. To string ：

    cast（'132' as signed） CONVERT('123',SIGNED); To int.

Available types 　

     Binary system , Syntaxis binary The effect of prefixes : BINARY
     Character , With parameters : CHAR()
     date : DATE
     Time : TIME
     Date time type : DATETIME
     Floating point numbers : DECIMAL
     Integers : SIGNED
     Unsigned integer : UNSIGNED