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ADD COLUMN
ADD INDEX
ADMIN
ADMIN CANCEL DDL
ADMIN CHECKSUM TABLE
ADMIN CHECK [TABLE|INDEX]
ADMIN SHOW DDL [JOBS|QUERIES]
ALTER DATABASE
ALTER INDEX
ALTER INSTANCE
ALTER TABLE
ALTER USER
ANALYZE TABLE
BACKUP
BEGIN
CHANGE COLUMN
COMMIT
CHANGE DRAINER
CHANGE PUMP
CREATE [GLOBAL|SESSION] BINDING
CREATE DATABASE
CREATE INDEX
CREATE ROLE
CREATE SEQUENCE
CREATE TABLE LIKE
CREATE TABLE
CREATE USER
CREATE VIEW
DEALLOCATE
DELETE
DESC
DESCRIBE
DO
DROP [GLOBAL|SESSION] BINDING
DROP COLUMN
DROP DATABASE
DROP INDEX
DROP ROLE
DROP SEQUENCE
DROP STATS
DROP TABLE
DROP USER
DROP VIEW
EXECUTE
EXPLAIN ANALYZE
EXPLAIN
FLASHBACK TABLE
FLUSH PRIVILEGES
FLUSH STATUS
FLUSH TABLES
GRANT <privileges>
GRANT <role>
INSERT
KILL [TIDB]
LOAD DATA
LOAD STATS
MODIFY COLUMN
PREPARE
RECOVER TABLE
RENAME INDEX
RENAME TABLE
REPLACE
RESTORE
REVOKE <privileges>
REVOKE <role>
ROLLBACK
SELECT
SET DEFAULT ROLE
SET [NAMES|CHARACTER SET]
SET PASSWORD
SET ROLE
SET TRANSACTION
SET [GLOBAL|SESSION] <variable>
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SHOW ERRORS
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mysql
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CREATE INDEX
This statement adds a new index to an existing table. It is an alternative syntax to ALTER TABLE .. ADD INDEX
, and included for MySQL compatibility.
Synopsis
CreateIndexStmt:
IndexKeyTypeOpt:
IfNotExists:
IndexTypeOpt:
IndexPartSpecificationList:
IndexOptionList:
IndexLockAndAlgorithmOpt:
IndexType:
IndexPartSpecification:
IndexOption:
IndexTypeName:
ColumnName:
OptFieldLen:
IndexNameList:
KeyOrIndex:
Examples
mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.10 sec)
mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+-------------------------+----------+-----------+---------------+--------------------------------+
| id | estRows | task | access object | operator info |
+-------------------------+----------+-----------+---------------+--------------------------------+
| TableReader_7 | 10.00 | root | | data:Selection_6 |
| └─Selection_6 | 10.00 | cop[tikv] | | eq(test.t1.c1, 3) |
| └─TableFullScan_5 | 10000.00 | cop[tikv] | table:t1 | keep order:false, stats:pseudo |
+-------------------------+----------+-----------+---------------+--------------------------------+
3 rows in set (0.00 sec)
mysql> CREATE INDEX c1 ON t1 (c1);
Query OK, 0 rows affected (0.30 sec)
mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| id | estRows | task | access object | operator info |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| IndexReader_6 | 10.00 | root | | index:IndexRangeScan_5 |
| └─IndexRangeScan_5 | 10.00 | cop[tikv] | table:t1, index:c1(c1) | range:[3,3], keep order:false, stats:pseudo |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
2 rows in set (0.00 sec)
mysql> ALTER TABLE t1 DROP INDEX c1;
Query OK, 0 rows affected (0.30 sec)
mysql> CREATE UNIQUE INDEX c1 ON t1 (c1);
Query OK, 0 rows affected (0.31 sec)
Expression index
Note:
Expression index is still an experimental feature. It is NOT recommended that you use it in the production environment.
To use this feature, make the following setting in TiDB Configuration File:
allow-expression-index = true
TiDB can build indexes not only on one or more columns in a table, but also on an expression. When queries involve expressions, expression indexes can speed up those queries.
Take the following query as an example:
SELECT * FROM t WHERE lower(name) = "pingcap";
If the following expression index is built, you can use the index to speed up the above query:
CREATE INDEX idx ON t ((lower(name)));
The cost of maintaining an expression index is higher than that of maintaining other indexes, because the value of the expression needs to be calculated whenever a row is inserted or updated. The value of the expression is already stored in the index, so this value does not require recalculation when the optimizer selects the expression index.
Therefore, when the query performance outweighs the insert and update performance, you can consider indexing the expressions.
Expression indexes have the same syntax and limitations as in MySQL. They are implemented by building indexes on generated virtual columns that are invisible, so the supported expressions inherit all limitations of virtual generated columns.
Currently, the optimizer can use the indexed expressions when the expressions are only in the FIELD
clause, WHERE
clause, and ORDER BY
clause. The GROUP BY
clause will be supported in future updates.
Invisible index
Invisible indexes are indexes that are ignored by the query optimizer:
CREATE TABLE t1 (c1 INT, c2 INT, UNIQUE(c2));
CREATE UNIQUE INDEX c1 ON t1 (c1) INVISIBLE;
For details, see ALTER INDEX
.
Associated session variables
The global variables associated with the CREATE INDEX
statement are tidb_ddl_reorg_worker_cnt
, tidb_ddl_reorg_batch_size
and tidb_ddl_reorg_priority
. Refer to system variables for details.
MySQL compatibility
FULLTEXT
,HASH
andSPATIAL
indexes are not supported.- Descending indexes are not supported (similar to MySQL 5.7).
- Adding the primary key constraint to a table is not supported by default. You can enable the feature by setting the
alter-primary-key
configuration item totrue
. For details, see alter-primary-key.