SQL #

SQL Support Status #

Compatible with all regular SQL when routing to single data node; The SQL routing to multiple data nodes is pretty complex, it divides the scenarios as totally supported, experimental supported and unsupported.

Totally Supported #

Fully support DML, DDL, DCL, TCL and most regular DAL. Support complex query with pagination, DISTINCT, ORDER BY, GROUP BY, aggregation and table JOIN.

Regular Query #

• SELECT Clause

SELECT select_expr [, select_expr ...] FROM table_reference [, table_reference ...]
[WHERE predicates]
[GROUP BY {col_name | position} [ASC | DESC], ...]
[ORDER BY {col_name | position} [ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]

• select_expr

*
| [DISTINCT] COLUMN_NAME [AS] [alias]
| (MAX | MIN | SUM | AVG)(COLUMN_NAME | alias) [AS] [alias]
| COUNT(* | COLUMN_NAME | alias) [AS] [alias]

• table_reference

tbl_name [AS] alias] [index_hint_list]
| table_reference ([INNER] | {LEFT|RIGHT} [OUTER]) JOIN table_factor [JOIN ON conditional_expr | USING (column_list)]

Subquery #

Stable supported when sharding keys are using in both subquery and outer query, and values of sharding keys are the same.

For example:

SELECT * FROM (SELECT * FROM t_order WHERE order_id = 1) o WHERE o.order_id = 1;

Stable supported for subquery with pagination.

For example:

SELECT * FROM (SELECT row_.*, rownum rownum_ FROM (SELECT * FROM t_order) row_ WHERE rownum <= ?) WHERE rownum > ?;

Sharding value in expression #

Sharding value in calculated expressions will lead to full routing.

For example, if create_time is sharding value:

SELECT * FROM t_order WHERE to_date(create_time, 'yyyy-mm-dd') = '2019-01-01';

Experimental Supported #

Experimental support specifically refers to use of Federation execution engine. The engine still in rapid development, basically available to users, but it still needs lots of optimization. It is an experimental product.

Subquery #

Experimental supported when sharding keys are not using for both subquery and outer query, or values of sharding keys are not the same.

For example:

SELECT * FROM (SELECT * FROM t_order) o;

SELECT * FROM (SELECT * FROM t_order) o WHERE o.order_id = 1;

SELECT * FROM (SELECT * FROM t_order WHERE order_id = 1) o;

SELECT * FROM (SELECT * FROM t_order WHERE order_id = 1) o WHERE o.order_id = 2;

Join with cross databases #

When tables in a join query are distributed on different database instances, sql statement will be supported by Federation execution engine. Assuming that t_order and t_order_item are sharding tables with multiple data nodes, and no binding table rules are configured, t_user and t_user_role are single tables that distributed on different database instances. Federation execution engine can support the following commonly used join query:

SELECT * FROM t_order o INNER JOIN t_order_item i ON o.order_id = i.order_id WHERE o.order_id = 1;

SELECT * FROM t_order o INNER JOIN t_user u ON o.user_id = u.user_id WHERE o.user_id = 1;

SELECT * FROM t_order o LEFT JOIN t_user_role r ON o.user_id = r.user_id WHERE o.user_id = 1;

SELECT * FROM t_order_item i LEFT JOIN t_user u ON i.user_id = u.user_id WHERE i.user_id = 1;

SELECT * FROM t_order_item i RIGHT JOIN t_user_role r ON i.user_id = r.user_id WHERE i.user_id = 1;

SELECT * FROM t_user u RIGHT JOIN t_user_role r ON u.user_id = r.user_id WHERE u.user_id = 1;

Unsupported #

CASE WHEN can not support as following:

• CASE WHEN containing sub-query
• CASE WHEN containing logical-table (instead of table alias)

SQL Example #