Diamond Notes

Thanks to David, our Jr. DBA, we get the tip of the day. Did you realize that NULL (the topic of another post here) is not equal to the empty string (’ ‘). It is true. If you compare a NULL and an empty string you can see this:

mysql> select ‘ ‘ is NULL;
+————-+
| ‘ ‘ is null |
+————-+
| 0 |
+————-+
1 row in set (0.05 sec)

mysql> select ‘ ‘ is not NULL;
+—————–+
| ‘ ‘ is not NULL |
+—————–+
| 1 |
+—————–+
1 row in set (0.00 sec)

The zero returned means false, the one means true. This has implications to your code. For example, since an empty string is not NULL it can be inserted into a column that is set to NOT NULL.

For a more in depth discussion take a look here: http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html