Question

I have a postgresql database which look like the following :

+---------------+---------------- ------+------------ ---+
|  id (bigint)  |  name (varying(255))  |  price (real)  |
+---------------+---------------- ------+------------ ---+
|       1       |          name 1       |        0.33    |
+---------------+---------------- ------+------------ ---+
|       1       |          name 2       |        1.33    |
+---------------+---------------- ------+------------ ---+
|       1       |          name 3       |        1       |
+---------------+---------------- ------+------------ ---+

And then the results of my queries :

SELECT * FROM my_table WHERE price = 1    -- OK (one row returned)
SELECT * FROM my_table WHERE price = 1.0  -- OK (one row returned)
SELECT * FROM my_table WHERE price = 1.33 -- FAIL (no row returned)
SELECT * FROM my_table WHERE price = 0.33 -- FAIL (no row returned)

When the value can’t be cast to an non-floating value no lines are returned by postgresql.

I can’t figure out why. Have you the same problem ? How can I fix this ?

Answer 1

One solution I see is to use explicit cast to real datatype:

SELECT * FROM my_table WHERE price = 0.33::real;
 id |  name  | price 
----+--------+-------
  1 | name 1 |  0.33

SELECT * FROM my_table WHERE price = 1.33::real;
 id |  name  | price 
----+--------+-------
  1 | name 2 |  1.33

According to documentation:

A numeric constant that contains neither a decimal point nor an
exponent is initially presumed to be type integer if its value fits in
type integer (32 bits); otherwise it is presumed to be type bigint if
its value fits in type bigint (64 bits); otherwise it is taken to be
type numeric. Constants that contain decimal points and/or exponents
are always initially presumed to be type numeric.

Note that:

SELECT 1.33::numeric = 1.33::real;
 ?column? 
----------
 f
(1 row)