MySQL 租户的字符串连接函数是 concat 、 concat_ws， ’||’ 默认是表示逻辑运算符`或`。

    如查看 MySQL 租户下的客户姓名，SQL语句如下：

    1. obclient> SELECT concat_ws(' ', c_first, c_last) full_name FROM cust ORDER BY c_last LIMIT 2;
    3. +---------------------------+
    4. | full_name                 |
    5. +---------------------------+
    6. | fvBZoeIV2uJh7 ABLEABLEESE |
    7. | dHmIgRV1IsC ABLEABLEOUGHT |
    8. +---------------------------+
    9. 2 rows in set (0.01 sec)

    如果把 MySQL 租户下的变量 sql_mode 值增加一个选项 PIPES_AS_CONCAT ，则 ’||’ 也会当作字符串连接符。SQL语句如下：

    1. obclient> SET SESSION sql_mode='PIPES_AS_CONCAT,STRICT_TRANS_TABLES,STRICT_ALL_TABLES';
    2. obclient> SELECT c_first || ' ' || c_last  full_name FROM cust ORDER BY c_last LIMIT 2;
    3. +---------------------------+
    4. | full_name                 |
    5. +---------------------------+
    6. | fvBZoeIV2uJh7 ABLEABLEESE |
    7. | dHmIgRV1IsC ABLEABLEOUGHT |
    8. +---------------------------+
    9. 2 rows in set (0.01 sec)