SQL #

SQL 支持程度 #

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。

稳定支持 #

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。

常规查询 #

SELECT 主语句

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)]

子查询 #

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 > ?;

运算表达式中包含分片键 #

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 #

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 #

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;

跨库关联查询 #

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;

不支持 #

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）

SQL 示例 #

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) > ?
SELECT col1, col2 FROM tbl_name UNION SELECT col1, col2 FROM tbl_name
SELECT col1, col2 FROM tbl_name UNION ALL SELECT col1, col2 FROM tbl_name

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