兼容全部常用的路由至单数据节点的 SQL； 路由至多数据节点的 SQL 由于场景复杂，分为稳定支持、实验性支持和不支持这三种情况。
全面支持 DML、DDL、DCL、TCL 和常用 DAL。 支持分页、去重、排序、分组、聚合、表关联等复杂查询。
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}]
* |
[DISTINCT] COLUMN_NAME [AS] [alias] |
(MAX | MIN | SUM | AVG)(COLUMN_NAME | alias) [AS] [alias] |
COUNT(* | COLUMN_NAME | alias) [AS] [alias]
tbl_name [AS] alias] [index_hint_list]
| table_reference ([INNER] | {LEFT|RIGHT} [OUTER]) JOIN table_factor [JOIN ON conditional_expr | USING (column_list)]
子查询和外层查询同时指定分片键，且分片键的值保持一致时，由内核提供稳定支持。
例如：
SELECT * FROM (SELECT * FROM t_order WHERE order_id = 1) o WHERE o.order_id = 1;
用于分页的子查询，由内核提供稳定支持。
例如：
SELECT * FROM (SELECT row_.*, rownum rownum_ FROM (SELECT * FROM t_order) row_ WHERE rownum <= ?) WHERE rownum > ?;
当分片键处于运算表达式中时，无法通过 SQL 字面提取用于分片的值，将导致全路由。
例如，假设 create_time 为分片键：
SELECT * FROM t_order WHERE to_date(create_time, 'yyyy-mm-dd') = '2019-01-01';
实验性支持特指使用 Federation 执行引擎提供支持。 该引擎处于快速开发中，用户虽基本可用，但仍需大量优化，是实验性产品。
子查询和外层查询未同时指定分片键，或分片键的值不一致时，由 Federation 执行引擎提供支持。
例如：
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;
当关联查询中的多个表分布在不同的数据库实例上时，由 Federation 执行引擎提供支持。
假设 t_order 和 t_order_item 是多数据节点的分片表，并且未配置绑定表规则，t_user 和 t_user_role 是分布在不同的数据库实例上的单表，那么 Federation 执行引擎能够支持如下常用的关联查询：
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;
以下 CASE WHEN 语句不支持：
CASE WHEN 中包含子查询CASE WHEN 中使用逻辑表名（请使用表别名）以下 UNION 和 UNION ALL 语句不支持：
| 稳定支持的 SQL | 必要条件 |
|---|---|
| SELECT * FROM tbl_name | |
| SELECT * FROM tbl_name WHERE (col1 = ? or col2 = ?) and col3 = ? | |
| SELECT * FROM tbl_name WHERE col1 = ? ORDER BY col2 DESC LIMIT ? | |
| SELECT COUNT(*), SUM(col1), MIN(col1), MAX(col1), AVG(col1) FROM tbl_name WHERE col1 = ? | |
| SELECT COUNT(col1) FROM tbl_name WHERE col2 = ? GROUP BY col1 ORDER BY col3 DESC LIMIT ?, ? | |
| SELECT DISTINCT * FROM tbl_name WHERE col1 = ? | |
| SELECT COUNT(DISTINCT col1), SUM(DISTINCT col1) FROM tbl_name | |
| (SELECT * FROM tbl_name) | |
| SELECT * FROM (SELECT * FROM tbl_name WHERE col1 = ?) o WHERE o.col1 = ? | 子查询和外层查询在同一分片后的数据节点 |
| INSERT INTO tbl_name (col1, col2,…) VALUES (?, ?, ….) | |
| INSERT INTO tbl_name VALUES (?, ?,….) | |
| INSERT INTO tbl_name (col1, col2, …) VALUES(1 + 2, ?, …) | |
| INSERT INTO tbl_name (col1, col2, …) VALUES (?, ?, ….), (?, ?, ….) | |
| INSERT INTO tbl_name (col1, col2, …) SELECT col1, col2, … FROM tbl_name WHERE col3 = ? | INSERT 表和 SELECT 表相同表或绑定表 |
| REPLACE INTO tbl_name (col1, col2, …) SELECT col1, col2, … FROM tbl_name WHERE col3 = ? | REPLACE 表和 SELECT 表相同表或绑定表 |
| UPDATE tbl_name SET col1 = ? WHERE col2 = ? | |
| DELETE FROM tbl_name WHERE col1 = ? | |
| CREATE TABLE tbl_name (col1 int, …) | |
| ALTER TABLE tbl_name ADD col1 varchar(10) | |
| DROP TABLE tbl_name | |
| TRUNCATE TABLE tbl_name | |
| CREATE INDEX idx_name ON tbl_name | |
| DROP INDEX idx_name ON tbl_name | |
| DROP INDEX idx_name |
| 实验性支持的 SQL | 必要条件 |
|---|---|
| SELECT * FROM (SELECT * FROM tbl_name) o | |
| SELECT * FROM (SELECT * FROM tbl_name) o WHERE o.col1 = ? | |
| SELECT * FROM (SELECT * FROM tbl_name WHERE col1 = ?) o | |
| SELECT * FROM (SELECT * FROM tbl_name WHERE col1 = ?) o WHERE o.col1 = ? | 子查询和外层查询不在同一分片后的数据节点 |
| SELECT (SELECT MAX(col1) FROM tbl_name) a, col2 from tbl_name | |
| SELECT SUM(DISTINCT col1), SUM(col1) FROM tbl_name | |
| SELECT col1, SUM(col2) FROM tbl_name GROUP BY col1 HAVING SUM(col2) > ? |
| 慢 SQL | 原因 |
|---|---|
| SELECT * FROM tbl_name WHERE to_date(create_time, ‘yyyy-mm-dd’) = ? | 分片键在运算表达式中，导致全路由 |
| 不支持的 SQL | 原因 | 解决方案 |
|---|---|---|
| INSERT INTO tbl_name (col1, col2, …) SELECT * FROM tbl_name WHERE col3 = ? | SELECT 子句不支持 * 和内置分布式主键生成器 | 无 |
| REPLACE INTO tbl_name (col1, col2, …) SELECT * FROM tbl_name WHERE col3 = ? | SELECT 子句不支持 * 和内置分布式主键生成器 | 无 |
| SELECT MAX(tbl_name.col1) FROM tbl_name | 查询列是函数表达式时，查询列前不能使用表名 | 使用表别名 |