SELECT

The SELECT statement is used to read data from TiDB.

Synopsis

SelectStmt:

SelectStmt

FromDual:

FromDual

WhereClauseOptional:

WhereClauseOptional

SelectStmtOpts:

SelectStmtOpts

SelectStmtFieldList:

SelectStmtFieldList

TableRefsClause:

TableRefsClause

WhereClauseOptional:

WhereClauseOptional

SelectStmtGroup:

SelectStmtGroup

HavingClause:

HavingClause

OrderByOptional:

OrderByOptional

SelectStmtLimit:

SelectStmtLimit

SelectLockOpt:

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.

SELECT

Synopsis

Description of the syntax elements

Examples

MySQL compatibility

See also