enum vs boolean in case of multiple yes/no fields
I don't like the enum datatype for various reasons.

Boolean in MySQL is actually a tinyint with 0 being false and 1 being true, or no and yes respectively.

BOOL, BOOLEAN

These types are synonyms for TINYINT(1). A value of zero is considered false. Nonzero values are considered true:

mysql&gt; SELECT IF(0, 'true', 'false');
+------------------------+
| IF(0, 'true', 'false') |
+------------------------+
| false                  |
+------------------------+

mysql&gt; SELECT IF(1, 'true', 'false');
+------------------------+
| IF(1, 'true', 'false') |
+------------------------+
| true                   |
+------------------------+

mysql&gt; SELECT IF(2, 'true', 'false');
+------------------------+
| IF(2, 'true', 'false') |
+------------------------+
| true                   |
+------------------------+

However, the values TRUE and FALSE are merely aliases for 1 and 0, respectively, as shown here:

mysql&gt; SELECT IF(0 = FALSE, 'true', 'false');
+--------------------------------+
| IF(0 = FALSE, 'true', 'false') |
+--------------------------------+
| true                           |
+--------------------------------+

mysql&gt; SELECT IF(1 = TRUE, 'true', 'false');
+-------------------------------+
| IF(1 = TRUE, 'true', 'false') |
+-------------------------------+
| true                          |
+-------------------------------+

mysql&gt; SELECT IF(2 = TRUE, 'true', 'false');
+-------------------------------+
| IF(2 = TRUE, 'true', 'false') |
+-------------------------------+
| false                         |
+-------------------------------+

mysql&gt; SELECT IF(2 = FALSE, 'true', 'false');
+--------------------------------+
| IF(2 = FALSE, 'true', 'false') |
+--------------------------------+
| false                          |
+--------------------------------+

The last two statements display the results shown because 2 is equal to neither 1 nor 0. 


Source.

FYI, this can be very useful for various other things. An example you can see in this answer I recently gave.