SQL

Since the syntax of SQL is flexible and complex and query situations of distributed databases and stand-alone databases are not identical with each other, SQLs incompatible with stand-alone databases are hard to avoid.

To try to avoid traps for users, this document has listed identified available SQL types and unavailable SQL types.

It is inevitably to have some SQLs that have not been listed yet, welcome to supplement for that. We will also try to support those unavailable SQLs in future versions.

Available SQL

Route to single data node

  • 100% compatible(MySQL only, other database dialect is doing).

Route to multiple data nodes or database beside MySQL

Fully available for DQL, DML, DDL, DCL, TCL and some DAL for MySQL. Available for pagination, DISTINCT, ORDER BY, GROUP BY, aggregation and JOIN(cannot support cross database). Here is an example of a most complex kind of DQL:

  • Main SELECT
SELECT select_expr [, select_expr ...] FROM table_reference [, table_reference ...]
[WHERE where_condition] 
[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)] | 

Unavailable SQL

Route to multiple data nodes or database beside MySQL

Unavailable for redundant parentheses, CASE WHEN, HAVING and UNION (ALL) and partly available for sub-query.

Available for not only sub-query of pagination (see pagination for detail), but also sub-query with equivalent pattern. No matter how many layers are nested, ShardingSphere can parse to the first sub-query that contains data table. Once it finds another sub-query of this kind in the sub-level nested, it will directly throw a parsing exception.

For example, the following sub-query is available for ShardingSphere:

SELECT COUNT(*) FROM (SELECT * FROM t_order o)

The following sub-query is unavailable:

SELECT COUNT(*) FROM (SELECT * FROM t_order o WHERE o.id IN (SELECT id FROM t_order WHERE status = ?))

To be simple, through sub-query, non-functional requirements are available in most cases, such as pagination, sum count and so on; but functional requirements are unavailable for now.

Due to the restriction of merger, sub-query that contains aggregate function is unavailable for now.

SQL that contains schema is unavailable, for the concept of ShardingSphere is to use multiple data source as one data source, so all the SQL visits are based on one logic schema.

Example

Available SQL

SQL Necessary conditions
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 ?, ?
INSERT INTO tbl_name (col1, col2,…) VALUES (?, ?, ….)
INSERT INTO tbl_name VALUES (?, ?,….)
INSERT INTO tbl_name (col1, col2, …) VALUES (?, ?, ….), (?, ?, ….)
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 Logic-index is configured in TableRule
SELECT DISTINCT * FROM tbl_name WHERE col1 = ?
SELECT COUNT(DISTINCT col1) FROM tbl_name

Unavailable SQL

SQL The reason of unavailability
INSERT INTO tbl_name (col1, col2, …) VALUES(1+2, ?, …) VALUES clause does not support operation expression
INSERT INTO tbl_name (col1, col2, …) SELECT col1, col2, … FROM tbl_name WHERE col3 = ? INSERT .. SELECT
INSERT INTO tbl_name SET col1 = ? INSERT .. SET
SELECT COUNT(col1) as count_alias FROM tbl_name GROUP BY col1 HAVING count_alias > ? HAVING
SELECT * FROM tbl_name1 UNION SELECT * FROM tbl_name2 UNION
SELECT * FROM tbl_name1 UNION ALL SELECT * FROM tbl_name2 UNION ALL
SELECT * FROM tbl_name1 WHERE (val1=?) AND (val1=?) Redundant parentheses
SELECT * FROM ds.tbl_name1 Contain schema(Supported if MySQL)
SELECT SUM(DISTINCT col1), SUM(col1) FROM tbl_name See DISTINCT availability detail

DISTINCT Availability Detail

Available SQL

SQL 所需条件
SELECT DISTINCT * FROM tbl_name WHERE col1 = ?
SELECT DISTINCT col1 FROM tbl_name
SELECT DISTINCT col1, col2, col3 FROM tbl_name
SELECT DISTINCT col1 FROM tbl_name ORDER BY col1
SELECT DISTINCT col1 FROM tbl_name ORDER BY col2
SELECT DISTINCT(col1) FROM tbl_name MySQL
SELECT AVG(DISTINCT col1) FROM tbl_name MySQL
SELECT SUM(DISTINCT col1) FROM tbl_name MySQL
SELECT COUNT(DISTINCT col1) FROM tbl_name MySQL
SELECT COUNT(DISTINCT col1) FROM tbl_name GROUP BY col1 MySQL
SELECT COUNT(DISTINCT col1 + col2) FROM tbl_name MySQL
SELECT COUNT(DISTINCT col1), SUM(DISTINCT col1) FROM tbl_name MySQL
SELECT COUNT(DISTINCT col1), col1 FROM tbl_name GROUP BY col1 MySQL
SELECT col1, COUNT(DISTINCT col1) FROM tbl_name GROUP BY col1 MySQL

Unavailable SQL

SQL Unavailable reason
SELECT SUM(DISTINCT col1), SUM(col1) FROM tbl_name Use normal aggregate function and DISTINCT aggregate function in the same time