- Introduction
- Concepts
- Architecture
- Key Features
- Horizontal Scalability
- MySQL Compatible Syntax
- Replicate from and to MySQL
- Distributed Transactions with Strong Consistency
- Cloud Native Architecture
- Minimize ETL with HTAP
- Fault Tolerance & Recovery with Raft
- Automatic Rebalancing
- Deployment and Orchestration with Ansible, Kubernetes, Docker
- JSON Support
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- Reference
- SQL
- MySQL Compatibility
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- Function and Operator Reference
- Type Conversion in Expression Evaluation
- Operators
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- Precision Math
- List of Expressions for Pushdown
- SQL Statements
ADD COLUMN
ADD INDEX
ADMIN
ADMIN CANCEL DDL
ADMIN CHECKSUM TABLE
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ADMIN SHOW DDL [JOBS|QUERIES]
ALTER DATABASE
ALTER INSTANCE
ALTER TABLE
ALTER USER
ANALYZE TABLE
BEGIN
CHANGE COLUMN
COMMIT
CREATE DATABASE
CREATE INDEX
CREATE ROLE
CREATE TABLE LIKE
CREATE TABLE
CREATE USER
CREATE VIEW
DEALLOCATE
DELETE
DESC
DESCRIBE
DO
DROP COLUMN
DROP DATABASE
DROP INDEX
DROP ROLE
DROP TABLE
DROP USER
DROP VIEW
EXECUTE
EXPLAIN ANALYZE
EXPLAIN
FLUSH PRIVILEGES
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GRANT <privileges>
GRANT <role>
INSERT
KILL [TIDB]
LOAD DATA
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RECOVER TABLE
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REVOKE <privileges>
REVOKE <role>
ROLLBACK
SELECT
SET DEFAULT ROLE
SET [NAMES|CHARACTER SET]
SET PASSWORD
SET ROLE
SET TRANSACTION
SET [GLOBAL|SESSION] <variable>
SHOW ANALYZE STATUS
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SHOW [FULL] COLUMNS FROM
SHOW CREATE TABLE
SHOW CREATE USER
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SHOW INDEX [FROM|IN]
SHOW KEYS [FROM|IN]
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SHOW TABLE REGIONS
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SPLIT REGION
START TRANSACTION
TRACE
TRUNCATE
UPDATE
USE
- Constraints
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- Views
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- Overview
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- The Blocklist of Optimization Rules and Expression Pushdown
- Introduction to Statistics
- TopN and Limit Push Down
- Optimizer Hints
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- Check the TiDB Cluster Status Using SQL Statements
- Execution Plan Binding
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- Glossary
Important
You are viewing the documentation of an older version of the TiDB database (TiDB v3.1).
It is recommended that you use the latest LTS version of the TiDB database.
SELECT
The SELECT
statement is used to read data from TiDB.
Synopsis
SelectStmt:
FromDual:
WhereClauseOptional:
SelectStmtOpts:
SelectStmtFieldList:
TableRefsClause:
WhereClauseOptional:
SelectStmtGroup:
HavingClause:
OrderByOptional:
SelectStmtLimit:
SelectLockOpt:
Description of the syntax elements
Syntax Element | Description |
---|---|
ALL , DISTINCT , DISTINCTROW | The ALL , DISTINCT /DISTINCTROW modifiers specify whether duplicate rows should be returned. ALL (the default) specifies that all matching rows should be returned. |
HIGH_PRIORITY | HIGH_PRIORITY gives the current statement higher priority than other statements. |
SQL_CALC_FOUND_ROWS | To guarantee compatibility with MySQL, TiDB parses this syntax, but will ignore it. |
SQL_CACHE , SQL_NO_CACHE | SQL_CACHE and SQL_NO_CACHE are used to control whether to cache the request results to the BlockCache of TiKV (RocksDB). For a one-time query on a large amount of data, such as the count(*) query, it is recommended to fill in SQL_NO_CACHE to avoid flushing the hot user data in BlockCache . |
STRAIGHT_JOIN | STRAIGHT_JOIN forces the optimizer to do a union query in the order of the tables used in the FROM clause. When the optimizer chooses a join order that is not good, you can use this syntax to speed up the execution of the query. |
select_expr | Each select_expr indicates a column to retrieve. including the column names and expressions. \* represents all the columns. |
FROM table_references | The FROM table_references clause indicates the table (such as select * from t; ), or tables (such as select * from t1 join t2; ) or even 0 tables (such as select 1+1 from dual; which is equivalent to select 1+1; ) from which to retrieve rows. |
WHERE where_condition | The WHERE clause, if given, indicates the condition or conditions that rows must satisfy to be selected. The result contains only the data that meets the condition(s). |
GROUP BY | The GROUP BY statement is used to group the result-set. |
HAVING where_condition | The HAVING clause and the WHERE clause are both used to filter the results. The HAVING clause filters the results of GROUP BY , while the WHERE clause filter the results before aggregation. |
ORDER BY | The ORDER BY clause is used to sort the data in ascending or descending order, based on columns, expressions or items in the select_expr list. |
LIMIT | The LIMIT clause can be used to constrain the number of rows. LIMIT takes one or two numeric arguments. With one argument, the argument specifies the maximum number of rows to return, the first row to return is the first row of the table by default; with two arguments, the first argument specifies the offset of the first row to return, and the second specifies the maximum number of rows to return. |
FOR UPDATE | The SELECT FOR UPDATE clause locks all the data in the result sets to detect concurrent updates from other transactions. Data that match the query conditions but do not exist in the result sets are not read-locked, such as the row data written by other transactions after the current transaction is started. TiDB uses the Optimistic Transaction Model. The transaction conflicts are not detected in the statement execution phase. Therefore, the current transaction does not block other transactions from executing UPDATE , DELETE or SELECT FOR UPDATE like other databases such as PostgreSQL. In the committing phase, the rows read by SELECT FOR UPDATE are committed in two phases, which means they can also join the conflict detection. If write conflicts occur, the commit fails for all transactions that include the SELECT FOR UPDATE clause. If no conflict is detected, the commit succeeds. And a new version is generated for the locked rows, so that write conflicts can be detected when other uncommitted transactions are being committed later. When using pessimistic transaction model, the behavior is basically the same as other databases. Refer to Difference with MySQL InnoDB to see the details. |
LOCK IN SHARE MODE | To guarantee compatibility, TiDB parses these three modifiers, but will ignore them. |
Examples
mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)
mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.03 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM t1;
+----+----+
| id | c1 |
+----+----+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
+----+----+
5 rows in set (0.00 sec)
MySQL compatibility
This statement is understood to be fully compatible with MySQL. Any compatibility differences should be reported via an issue on GitHub.
See also
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