Don't sum up columns with + in a sql-query if NULL-Values can be present.

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MySQL and PostgreSQL cannot sum up NULL values with the + value. The sum value will be NULL.

MySQL:

mysql> select 1 + 2 + 3;
+-----------+
| 1 + 2 + 3 |
+-----------+
|         6 |
+-----------+
1 row in set (0,00 sec)

mysql> select 1 + NULL + 3;
+--------------+
| 1 + NULL + 3 |
+--------------+
|         NULL |
+--------------+
1 row in set (0,00 sec)

Postgres:

test_database=# select 1 + 2 + 3;

 ?column? 
----------
        6
(1 row)

test_database=# select 1 + NULL + 3;

 ?column? 
----------
         
(1 row)

If you want to do additions in the database:

• use SUM if it's an option to sum up a column of a result set instead of expressions (SUM ignores NULL values)
• wrap columns with: COALESCE(column, 0)(COALESCE takes the first non-null argument)