OR, ||Logical OR. When both operands are non-NULL, the result is 1 if any operand is non-zero, and 0 otherwise. With a NULL operand, the result is 1 if the other operand is non-zero, and NULL otherwise. If both operands are NULL, the result is NULL.
For this operator, short-circuit evaluation can be used.
In Oracle mode, || ignores null.
SELECT 1 || 1;
+--------+
| 1 || 1 |
+--------+
| 1 |
+--------+
SELECT 1 || 0;
+--------+
| 1 || 0 |
+--------+
| 1 |
+--------+
SELECT 0 || 0;
+--------+
| 0 || 0 |
+--------+
| 0 |
+--------+
SELECT 0 || NULL;
+-----------+
| 0 || NULL |
+-----------+
| NULL |
+-----------+
SELECT 1 || NULL;
+-----------+
| 1 || NULL |
+-----------+
| 1 |
+-----------+In Oracle mode:
SELECT 0 || NULL;
+-----------+
| 0 || NULL |
+-----------+
| 0 |
+-----------+This page is licensed: GPLv2, originally from fill_help_tables.sql