Why is the result of `select 'a'=0;` 1?

Question

mysql> SELECT \'a\'=\'b\'=\'c\';
+-------------+
| \'a\'=\'b\'=\'c\' |
+-------------+
|           1 |
+-------------+
mysql> select \'a\'=0, \'b\'=\'c\';
+---         


        

Answer 1

TEXT values are cast to INTEGER values by interpreting all the leading digits as a number. If there are no digits, it casts to 0.

So:

'123a' = 123
'4a' = 4
'a' = 0