CAST to DECIMAL in MySQL

I am trying to cast to Decimal in MySQL like this:

CAST((COUNT(*) * 1.5) AS DECIMAL(2))

I'm trying to convert the number of rows in a table (times 1.5) to a floating point number with two digits after the point.

SQL code:

 SELECT CONCAT(Guardian.title, ' ', Guardian.forename, ' ', Guardian.surname) AS 'Guardian Name', COUNT(*) AS 'Number of Activities', (COUNT(*) * 1.5) AS 'Cost' FROM Schedule INNER JOIN Child ON Schedule.child_id = Child.id INNER JOIN Guardian ON Child.guardian = Guardian.id GROUP BY Guardian ORDER BY Guardian.surname, Guardian.forename ASC

It produces an error:

#1064 - You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use
near 'CAST((COUNT(*) * 1.5) AS DECIMAL(12,2))' at line 1.

Another try, this cast also doesn't work:

 SELECT CONCAT(Guardian.title, ' ', Guardian.forename, ' ', Guardian.surname) AS 'Guardian Name', COUNT(*) AS 'Number of Activities', CAST((COUNT(*) * 1.5) AS DECIMAL(8,2)) AS 'Cost' FROM Schedule INNER JOIN Child ON Schedule.child_id = Child.id INNER JOIN Guardian ON Child.guardian = Guardian.id GROUP BY Guardian ORDER BY Guardian.surname, Guardian.forename ASC

How do I use mysql to cast from integer to decimal?

5 Answers

From MySQL docs: Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC:

In standard SQL, the syntax DECIMAL(M) is equivalent to DECIMAL(M,0)

So, you are converting to a number with 2 integer digits and 0 decimal digits. Try this instead:

CAST((COUNT(*) * 1.5) AS DECIMAL(12,2)) 

MySQL casts to Decimal:

Cast bare integer to decimal:

select cast(9 as decimal(4,2)); //prints 9.00

Cast Integers 8/5 to decimal:

select cast(8/5 as decimal(11,4)); //prints 1.6000

Cast string to decimal:

select cast(".885" as decimal(11,3)); //prints 0.885

Cast two int variables into a decimal

mysql> select 5 into @myvar1;
Query OK, 1 row affected (0.00 sec)
mysql> select 8 into @myvar2;
Query OK, 1 row affected (0.00 sec)
mysql> select @myvar1/@myvar2; //prints 0.6250

Cast decimal back to string:

select cast(1.552 as char(10)); //shows "1.552"

DECIMAL has two parts: Precision and Scale. So part of your query will look like this:

CAST((COUNT(*) * 1.5) AS DECIMAL(8,2))

Precision represents the number of significant digits that are stored for values.
Scale represents the number of digits that can be stored following the decimal point.

I'm lazy:

0 + colname

Furthermore, this works for fixed with any number of decimal places, float, etc.

See also ROUND() and FORMAT().

An alternative, I think for your purpose, is to use the round() function:

select round((10 * 1.5),2) // prints 15.00

You can try it here: