str 函数 将小数转换为varchar类型

float_expression                               

Is an expression of approximate numeric (float) data type with a decimal point.                

length                               

Is the total length. This includes decimal point, sign, digits, and spaces. The default is 10.

decimal                               

Is the number of places to the right of the decimal point. decimal must be less than or equal to 16. If decimal is more than 16 then the result is truncated to sixteen places to the right of the decimal point.

SELECT STR(123.45, 6, 1);

结果是 123.5，类型是Varchar