Since the SQL syntax is flexible and complex and distributed databases and stand-alone databases do not have identical query sceanrios, SQLs incompatible with stand-alone databases are hard to avoid.
This document has listed identified supported SQL types and unsupported SQL types, trying to avoid traps for users.
It is inevitably to have some unlisted SQLs, welcome to supplement for that. We will also try to support those unavailable SQLs in future versions.
Fully support DML, DDL, DCL, TCL and some DAL. Support pagination, DISTINCT, ORDER BY, GROUP BY, aggregation and JOIN (does not support cross-database relevance). Here is an example of a most complex kind of DML:
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)]
Do not support CASE WHEN, HAVING and UNION (ALL) and partly available sub-query.
Support not only pagination sub-query (see pagination for more details), but also sub-query with the same mode. 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:
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 aggregation function is unavailable for now.
Do not support SQL that contains schema, 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.
ShardingColumn in expressions and functions will lead to full routing.
The following SQL is unavailable to single sharding, if create_time is shardingColumn:
SELECT * FROM t_order WHERE to_date(create_time, 'yyyy-mm-dd') = '2019-01-01';
ShardingSphere extract the value of ShardingColumn through literal of SQL, so ShardingSphere can not calculate the sharding value from the SQL because the data inside the expression is in database.
When shardingColumn in expressions and functions, ShardingSphere will use full routing to get results.
| 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 | |
| SELECT DISTINCT * FROM tbl_name WHERE col1 = ? | |
| SELECT COUNT(DISTINCT col1) FROM tbl_name |
| SQL | Reason |
|---|---|
| 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 |
| 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 ds.tbl_name1 | Contain schema |
| SELECT SUM(DISTINCT col1), SUM(col1) FROM tbl_name | See DISTINCT availability detail |
| SELECT * FROM tbl_name WHERE to_date(create_time, ‘yyyy-mm-dd’) = ? | Lead to full routing |
| SQL |
|---|
| 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 |
| SELECT AVG(DISTINCT col1) FROM tbl_name |
| SELECT SUM(DISTINCT col1) FROM tbl_name |
| SELECT COUNT(DISTINCT col1) FROM tbl_name |
| SELECT COUNT(DISTINCT col1) FROM tbl_name GROUP BY col1 |
| SELECT COUNT(DISTINCT col1 + col2) FROM tbl_name |
| SELECT COUNT(DISTINCT col1), SUM(DISTINCT col1) FROM tbl_name |
| SELECT COUNT(DISTINCT col1), col1 FROM tbl_name GROUP BY col1 |
| SELECT col1, COUNT(DISTINCT col1) FROM tbl_name GROUP BY col1 |
| SQL | Reason |
|---|---|
| SELECT SUM(DISTINCT col1), SUM(col1) FROM tbl_name | Use normal aggregation function and DISTINCT aggregation function in the same time |