Question

I’m baffled as to what this SQL statement means:

SELECT exhibitor_categories+0 from exhibitor_registry

What is exhibitor_categories+0 ? It returns a number for each row returned.

exhibitor_categories is defined as:

set('contemporary', 'classical impression / transitional', 'outdoor', 'home accessories')

Thanks for your time 🙂

Answer 1

It implicity converts the set value to an INTEGER.

A set is treated as a bitmap, so the first value sets bit 0, the second value sets bit 1 etc.

mysql> CREATE TABLE exhibitor_registry(exhibitor_categories set('contemporary',
'classical impression / transitional', 'outdoor', 'home accessories') NOT NULL);

Query OK, 0 rows affected (0.08 sec)

mysql> INSERT
    -> INTO    exhibitor_registry
    -> VALUES  ('contemporary,classical impression / transitional,outdoor');
Query OK, 1 row affected (0.03 sec)

mysql> SELECT  exhibitor_categories
    -> FROM    exhibitor_registry;
+----------------------------------------------------------+
| exhibitor_categories                                     |
+----------------------------------------------------------+
| contemporary,classical impression / transitional,outdoor |
+----------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT  exhibitor_categories + 0
    -> FROM    exhibitor_registry;
+--------------------------+
| exhibitor_categories + 0 |
+--------------------------+
|                        7 |
+--------------------------+
1 row in set (0.00 sec)