OR
运算符说明
OR,||
逻辑运算符用作逻辑或运算。当两个操作数都非 null
时,如果操作数同时也非零,则返回结果为 true
,否则为 false
;对于 NULL
操作数,如果另一个操作数非零,则返回结果为 true
,否则为 NULL
;如果两个操作数都为 NULL
,则返回结果为 NULL
。
语法结构
> SELECT column_1 OR column_2 FROM table_name;
示例
mysql> select 1 or 1;
+--------+
| 1 or 1 |
+--------+
| true |
+--------+
1 row in set (0.01 sec)
mysql> select 1 or 0;
+--------+
| 1 or 0 |
+--------+
| true |
+--------+
1 row in set (0.00 sec)
mysql> select 0 or 0;
+--------+
| 0 or 0 |
+--------+
| false |
+--------+
1 row in set (0.01 sec)
mysql> select 0 or null;
+-----------+
| 0 or null |
+-----------+
| NULL |
+-----------+
1 row in set (0.00 sec)
mysql> select 1 or null;
+-----------+
| 1 or null |
+-----------+
| true |
+-----------+
1 row in set (0.00 sec)
create table t1 (a boolean,b bool);
insert into t1 values (0,1),(true,false),(true,1),(0,false),(NULL,NULL);
mysql> select a or b from t1;
+--------+
| a or b |
+--------+
| true |
| true |
| true |
| false |
| NULL |
+--------+
5 rows in set (0.00 sec)