MySQL - Table 'my_table' was not locked with Lock Tables

If in one session, you locked one table but want to select from another table, you must either lock that table too or unlock all tables.

mysql> LOCK TABLES t1 READ;
mysql> SELECT COUNT(*) FROM t1;
+----------+
| COUNT(*) |
+----------+
|        3 |
+----------+
mysql> SELECT COUNT(*) FROM t2;
ERROR 1100 (HY000): Table 't2' was not locked with LOCK TABLES

The solution for me was to unlock the tables. They had been locked by a previous query which failed before reaching the unlock tables statement.

UNLOCK TABLES
SELECT ...