SQL

Since the SQL syntax is flexible and complex and distributed databases and stand-alone databases do not have identical query scenarios, 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.

Supported SQL

Route to single data node

  • 100% compatible(MySQL only, we are completing other databases).

Route to multiple data nodes

Fully support DML, DDL, DCL, TCL and some DAL. Support pagination, DISTINCT, ORDER BY, GROUP BY, aggregation and JOIN. Here is an example of a most complex kind of DML:

  • Main SELECT
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)]

Unsupported SQL

Route to multiple data nodes

Partially support CASE WHEN

  • CASE WHEN containing sub-query is not supported
  • CASE WHEN containing logical-table is not supported(please use alias of table)

Do not support UNION (ALL)

Partly available sub-query

  • If subquery and outer query specify sharding key at the same time, the value of sharding key must be consistent.

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

The following sub-query is unavailable:

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

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.

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.

Operation for shardingColumn

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.

Example

Supported 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 ?, ?
SELECT col1, SUM(col2) FROM tbl_name GROUP BY col1 HAVING SUM(col2) > 10
SELECT DISTINCT * FROM tbl_name WHERE col1 = ?
SELECT COUNT(DISTINCT col1) FROM tbl_name
SELECT subquery_alias.col1 FROM (select tbl_name.col1 from tbl_name where tbl_name.col2=?) subquery_alias
SELECT (SELECT MAX(col1) FROM tbl_name) a, col2 from tbl_name
(SELECT * FROM tbl_name)
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 = ? The table inserted and the table selected must be the same or bind tables
REPLACE INTO tbl_name (col1, col2, …) SELECT col1, col2, … FROM tbl_name WHERE col3 = ? The table replaced and the table selected must be the same or bind tables
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

Unsupported SQL

SQL Reason
INSERT INTO tbl_name (col1, col2, …) SELECT * FROM tbl_name WHERE col3 = ? SELECT clause does not support *-shorthand and built-in key generators
REPLACE INTO tbl_name (col1, col2, …) SELECT * FROM tbl_name WHERE col3 = ? SELECT clause does not support *-shorthand and built-in key generators
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_name WHERE to_date(create_time, ‘yyyy-mm-dd’) = ? Lead to full routing
SELECT MAX(tbl_name.col1) FROM tbl_name The select function item contains TableName. Otherwise, If this query table had an alias, then TableAlias could work well in select function items.

DISTINCT Availability Explanation

Supported SQL

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 SUM(DISTINCT col1), SUM(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

Unsupported SQL

SQL Reason
SELECT SUM(DISTINCT tbl_name.col1), tbl_name.col2 FROM tbl_name The select function item contains TableName. Otherwise, If this query table had an alias, then TableAlias could work well in select function items.