how pdo_sqlsrv driver convert float type to string?

Question

I set some table's column type to float and length to 53, set it's value is 38.8, when i use sqlsrv driver for a query, it's ok , it's show value is 38.8. But,when i use pdo_sqlsrv driver for a query ,it's show value is 38.799999999999997, it's why?

Answer 1

Decimal number 38.8 is periodic when converted to binary:

100110.1100110011001100110011001100110011001100110011001100110011001100110
       ^^^^
       Repeats forever

Thus it cannot be stored exactly in a computer if you chose a regular numeric format (which always have fixed storage sizes).

It doesn't really matter: since you've established you only want 8 decimals, you should get the correct value when discarding the rest:

ini_set('precision', 30);
var_dump( 38.8, number_format(38.8, 8) );

float(38.7999999999999971578290569596)
string(11) "38.80000000"

However, if 8 ^th decimal is actually important for you, you should switch the column type to DECIMAL , which stores numbers internally as strings, thus keeps the exact decimal representation.