格式化浮点数 format(number, length);

Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. If D is 0, the result has no decimal point or fractional part. D should be a constant value.

mysql> SELECT FORMAT(12332.123456, 4);
       -> '12,332.1235'
mysql> SELECT FORMAT(12332.1,4);
       -> '12,332.1000'
mysql> SELECT FORMAT(12332.2,0);
      -> '12,332'

rpad 和 lpad 给定位数,不足补充自定义字符
Returns the string str,right-padded with the string padstr to a length of len characters. If
str is longer than len, the return value is shortened to len characters.

mysql> SELECT RPAD('hi',5,'?'); 
            -> 'hi???'
 mysql> SELECT RPAD('hi',1,'?'); 
           -> 'h'
mysql>SELET RPAD(12, 5 ,0);

This function is multi-byte safe. 


Returns the string str, left-padded with the string padstr to a length of lencharacters. If str is longer than len, the return value is shortened to lencharacters.

mysql> SELECT LPAD('hi',4,'??');
       -> '??hi'
mysql> SELECT LPAD('hi',1,'??');
      -> 'h'

mysql>SELECT LPAD(12, 5 , 0)