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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)