DML Statements

Last updated: 2020-09-14 11:02:56

    select

    We recommend including the shardkey field whose hash value allows the direct routing of SQL request through the proxy to the database instance. Otherwise, the proxy needs to send requests to all database instances in the cluster and aggregates the results, which degrades performance:

    mysql> select * from test1 where a=2;
    +------+------+---------+
    | a    | b    | c       |
    +------+------+---------+
    |    2 |    3 | record2 |
    |    2 |    4 | record3 |
    +------+------+---------+
    2 rows in set (0.00 sec)

    insert/replace

    Include the shardkey field to avoid errors, because the proxy is unable to determine the target backend database for SQL.

    mysql> insert into test1 (b,c) values(4,"record3");
    ERROR 810 (HY000): Proxy ERROR:sql is too complex,need to send to only noshard table.
        Shard table insert must has field spec
    
    mysql> insert into test1 (a,c) values(4,"record3");
    Query OK, 1 row affected (0.01 sec)

    delete/update

    For security reasons, include the where condition to avoid errors.

    mysql> delete from test1;
    ERROR 810 (HY000): Proxy ERROR:sql is too complex,need to send to only noshard table.
        Shard table delete/update must have a where clause
    
    mysql> delete from test1 where a=1;
    Query OK, 1 row affected (0.01 sec)

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