如何显示由SET运算符初始化的所有变量？

Question

MariaDB [(none)]> SET @good = 10;
    Query OK, 0 rows affected (0.00 sec)

    MariaDB [(none)]> SHOW VARIABLES LIKE 'good';
    Empty set (0.07 sec)

如何显示由SET运算符初始化的所有变量？

Answer 1

对于MySQL，请使用：

select * from performance_schema.user_variables_by_thread;

MySQL演示：

mysql> SET @good = 10;
Query OK, 0 rows affected (0.00 sec)

mysql> SET @bad = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.user_variables_by_thread;
+-----------+---------------+----------------+
| THREAD_ID | VARIABLE_NAME | VARIABLE_VALUE |
+-----------+---------------+----------------+
|     36922 | bad           | 0              |
|     36922 | good          | 10             |
+-----------+---------------+----------------+
2 rows in set (0.00 sec)

对于MariaDB，目前尚不支持：

https://mariadb.com/kb/en/mariadb/information-schema-user_variables-table/

<强> The USER_VARIABLES table will be introduced in MariaDB 10.2.0 as part of the user_variables plugin.