运算符优先级

本文介绍了PolarDB-X中运算符的优先级。

PolarDB-X操作符的优先级由高到低，如下所示：

特殊说明

IN/NOT IN与=优先级

在MySQL 5.7.19中执行如下SQL：

mysql> select binary 'a' = 'a' in (1, 2, 3);
+-------------------------------+
| binary 'a' = 'a' in (1, 2, 3) |
+-------------------------------+
|                             1 |
+-------------------------------+
1 row in set, 1 warning (0.01 sec)
mysql> show warnings;
+---------+------+---------------------------------------+
| Level   | Code | Message                               |
+---------+------+---------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'a' |
+---------+------+---------------------------------------+
1 row in set (0.00 sec)
mysql> select 1 in (1, 2, 3) = 'a';
+----------------------+
| 1 in (1, 2, 3) = 'a' |
+----------------------+
|                    0 |
+----------------------+
1 row in set, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+---------------------------------------+
| Level   | Code | Message                               |
+---------+------+---------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'a' |
+---------+------+---------------------------------------+
1 row in set (0.00 sec)

可见，在MySQL中，IN/NOT IN的优先级高于=（比较运算符），在PolarDB-X中，严格按照以上优先级实现，在优先级相同的情况下，采用左结合的方式。