SELECT

Syntax

SELECT [ALL | DISTINCT | DISTINCTROW] [HIGH_PRIORITY] [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS] select_expr [, select_expr ...] [ FROM table_references [WHERE where_condition] [GROUP BY {col_name | expr | position} [ASC | DESC], ... [WITH ROLLUP]] [HAVING where_condition] [ORDER BY {col_name | expr | position} [ASC | DESC], ...] [LIMIT {[offset,] row_count | row_count OFFSET offset [ROWS EXAMINED rows_limit] } ] procedure|[PROCEDURE procedure_name(argument_list)] [INTO OUTFILE 'file_name' [CHARACTER SET charset_name] [export_options] | INTO DUMPFILE 'file_name' | INTO var_name [, var_name] ] [FOR UPDATE lock_option | LOCK IN SHARE MODE lock_option]

export_options: [{FIELDS | COLUMNS} [TERMINATED BY 'string'] [[OPTIONALLY] ENCLOSED BY 'char'] [ESCAPED BY 'char'] ] [LINES [STARTING BY 'string'] [TERMINATED BY 'string'] ]

lock_option: [WAIT n | NOWAIT | SKIP LOCKED]

Description

SELECT is used to retrieve rows selected from one or more tables, and can include UNION statements and subqueries.

  • Each select_expr expression indicates a column or data that you want to retrieve. You must have at least one select expression. See Select Expressions below.
  • The FROM clause indicates the table or tables from which to retrieve rows. Use either a single table name or a JOIN expression. See JOIN for details. If no table is involved, FROM DUAL can be specified.
  • Each table can also be specified as db_name.tabl_name. Each column can also be specified as tbl_name.col_name or even db_name.tbl_name.col_name. This allows one to write queries which involve multiple databases. See Identifier Qualifiers for syntax details.
  • The WHERE clause, if given, indicates the condition or conditions that rows must satisfy to be selected. where_condition is an expression that evaluates to true for each row to be selected. The statement selects all rows if there is no WHERE clause.
  • Use the ORDER BY clause to order the results.
  • Use the LIMIT clause allows you to restrict the results to only a certain number of rows, optionally with an offset.
  • Use the GROUP BY and HAVING clauses to group rows together when they have columns or computed values in common.

SELECT can also be used to retrieve rows computed without reference to any table.

Select Expressions

A SELECT statement must contain one or more select expressions, separated by commas. Each select expression can be one of the following:

  • The name of a column.
  • Any expression using functions and operators.
  • * to select all columns from all tables in the FROM clause.
  • tbl_name.* to select all columns from just the table tbl_name.

When specifying a column, you can either use just the column name or qualify the column name with the name of the table using tbl_name.col_name. The qualified form is useful if you are joining multiple tables in the FROM clause. If you do not qualify the column names when selecting from multiple tables, MariaDB will try to find the column in each table. It is an error if that column name exists in multiple tables.

You can quote column names using backticks. If you are qualifying column names with table names, quote each part separately as `tbl_name`.`col_name`.

If you use any grouping functions in any of the select expressions, all rows in your results will be implicitly grouped, as if you had used GROUP BY NULL.

DISTINCT

A query may produce some identical rows. By default, all rows are retrieved, even when their values are the same. To explicitly specify that you want to retrieve identical rows, use the ALL option. If you want duplicates to be removed from the resultset, use the DISTINCT option. DISTINCTROW is a synonym for DISTINCT. See also COUNT DISTINCT and SELECT UNIQUE in Oracle mode.

INTO

The INTO clause is used to specify that the query results should be written to a file or variable.

The reverse of SELECT INTO OUTFILE is LOAD DATA.

LIMIT

Restricts the number of returned rows. See LIMIT and LIMIT ROWS EXAMINED for details.

LOCK IN SHARE MODE/FOR UPDATE

See LOCK IN SHARE MODE and FOR UPDATE for details on the respective locking clauses.

OFFSET ... FETCH

MariaDB starting with 10.6

See SELECT ... OFFSET ... FETCH.

ORDER BY

Order a resultset. See ORDER BY for details.

PARTITION

Specifies to the optimizer which partitions are relevant for the query. Other partitions will not be read. See Partition Pruning and Selection for details.

PROCEDURE

Passes the whole result set to a C Procedure. See PROCEDURE and PROCEDURE ANALYSE (the only built-in procedure not requiring the server to be recompiled).

SKIP LOCKED

MariaDB starting with 10.6

The SKIP LOCKED clause was introduced in MariaDB 10.6.0.

This causes those rows that couldn't be locked (LOCK IN SHARE MODE or FOR UPDATE) to be excluded from the result set. An explicit NOWAIT is implied here. This is only implemented on InnoDB tables and ignored otherwise.

SQL_CALC_FOUND_ROWS

When SQL_CALC_FOUND_ROWS is used, then MariaDB will calculate how many rows would have been in the result, if there would be no LIMIT clause. The result can be found by calling the function FOUND_ROWS() in your next sql statement.


MariaDB starting with 10.1.2

max_statement_time clause

By using max_statement_time in conjunction with SET STATEMENT, it is possible to limit the execution time of individual queries. For example:

SET STATEMENT max_statement_time=100 FOR 
  SELECT field1 FROM table_name ORDER BY field1;

WAIT/NOWAIT

Set the lock wait timeout. See WAIT and NOWAIT.

Examples

SELECT f1,f2 FROM t1 WHERE (f3<=10) AND (f4='y');

See Getting Data from MariaDB (Beginner tutorial), or the various sub-articles, for more examples.

See Also

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