# Selecting Data - [DUAL](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/dual.md): Understand the DUAL table. This dummy table allows selecting values without referencing a real table, often used for calculations or retrieving system variables. - [FOR UPDATE](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/for-update.md): Lock rows for write operations. This clause prevents other transactions from modifying or reading the selected rows until the current transaction ends. - [GROUP BY](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/group-by.md): Group result sets by one or more columns. Learn to aggregate data using functions like SUM, COUNT, and AVG in conjunction with grouping. - [LIMIT](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/limit.md): Complete LIMIT clause reference: LIMIT n, LIMIT offset,row\_count, LIMIT row\_count OFFSET offset syntax, ORDER BY result handling, and UPDATE replication safety. - [LOCK IN SHARE MODE](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/lock-in-share-mode.md): Read rows with a shared lock. This clause ensures rows remain unchanged by other transactions while allowing other sessions to read them. - [ORDER BY](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/order-by.md): Complete ORDER BY clause: sort SELECT/UPDATE/DELETE results with ASC/DESC, multiple expressions, integer column positions, GROUP BY/LIMIT usage. - [PROCEDURE](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/procedure.md): Pass query results to a C procedure. This clause allows processing the result set on the server side before returning it to the client. - [SELECT](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/select.md): Complete guide to SELECT queries in MariaDB. Complete syntax reference for joins, subqueries, WHERE clauses, GROUP BY, and aggregate functions. - [SELECT INTO DUMPFILE](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/select-into-dumpfile.md): Export a single row to a file without formatting. This statement writes raw binary data, such as BLOBs, directly to a file on the server. - [SELECT INTO OUTFILE](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/select-into-outfile.md): Complete guide to SELECT queries in MariaDB. Complete syntax reference for joins, subqueries, WHERE clauses, GROUP BY, and aggregate functions. - [SELECT ... OFFSET ... FETCH](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/select-offset-fetch.md): Pagination using standard SQL syntax. This clause limits the number of rows returned and skips a specified number of rows, similar to LIMIT. - [SELECT WITH ROLLUP](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/select-with-rollup.md): Generate super-aggregate summaries. This modifier adds extra rows to the result set representing subtotals and grand totals for grouped columns. - [Common Table Expressions (CTE)](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/common-table-expressions.md): Learn about Common Table Expressions (CTEs) in MariaDB Server. This section explains how to use CTEs for complex, readable, and reusable subqueries, simplifying data selection and manipulation. - [Recursive Common Table Expressions Overview](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/common-table-expressions/recursive-common-table-expressions-overview.md): Process hierarchical data using recursive CTEs. These expressions reference themselves to repeatedly execute a subquery, perfect for traversing tree structures or generating sequences. - [Non-Recursive Common Table Expressions Overview](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/common-table-expressions/non-recursive-common-table-expressions-overview.md): Define simple temporary result sets. Non-recursive CTEs act like query-local views, improving readability by allowing you to define and reuse subqueries within a single statement. - [WITH](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/common-table-expressions/with.md): Complete WITH clause reference: WITH \[RECURSIVE] AS (SELECT...) syntax, recursive CTE support, CYCLE...RESTRICT cycle detection, and max\_recursive\_iterations. - [Joins](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/joins.md): Retrieve data from multiple tables based on related columns. This section covers INNER, LEFT, RIGHT, and CROSS JOIN syntax and usage. - [JOIN Syntax](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/joins/join-syntax.md): Complete reference for JOIN Syntax in MariaDB. Complete syntax guide with all options, clauses, and practical examples with comprehensive examples and best. - [Comma vs JOIN](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/joins/comma-vs-join.md): Compare implicit and explicit join syntax. This article explains why using the explicit JOIN syntax with an ON clause is preferred over comma-separated tables for readability and precedence. - [Set Operations](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations.md): SQL set operations combine the results of multiple query blocks in a single result, using the standard SQL operators EXCEPT, INTERSECT, and UNION, and the Oracle operator MINUS. - [Precedence Control in Table Operations](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations/precedence-control-in-table-operations.md): Control the execution order of UNION, EXCEPT, and INTERSECT operations. Learn how to use parentheses to define explicit operation priority. - [EXCEPT](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations/except.md): Return rows from the first result set that do not appear in the second. This set operator performs a subtraction of two datasets. - [INTERSECT](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations/intersect.md) - [MINUS](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations/minus.md): Oracle-compatible synonym for the EXCEPT operator. It returns rows from the first query that are not present in the second query. - [UNION](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/set-operations/union.md): Combine results from multiple SELECT statements into a single result set. This operator can optionally remove duplicates or include all rows. - [Subqueries](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries.md): Nest queries within other SQL statements. Learn to use scalar, column, row, and table subqueries to filter or calculate data dynamically. - [Subqueries With ALL](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-and-all.md): Compare a value against all results from a subquery. The ALL operator returns TRUE if the comparison holds for every row returned by the subquery. - [Subqueries With ANY and SOME](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-and-any.md): Compare a value against any result from a subquery. The ANY (or SOME) operator returns TRUE if the comparison holds for at least one row. - [Subqueries with IN and NOT IN](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-with-in-and-not-in.md) - [Subqueries With EXISTS](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-and-exists.md): Test for the existence of rows. The EXISTS operator returns TRUE if the subquery returns at least one row, often used for correlated subqueries. - [Subqueries With JOINs](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-and-joins.md): Understand when to use subqueries versus joins. This guide explains performance implications and how to rewrite subqueries as joins for efficiency. - [Subqueries in a FROM Clause (Derived Tables)](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-in-a-from-clause-derived-tables.md): Use a subquery as a temporary table. Derived tables allow you to select from the result set of another query within the FROM clause. - [Row Subqueries](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-row-subqueries.md): Retrieve a single row of multiple values. A row subquery returns a tuple that can be compared against a row constructor in the outer query. - [Scalar Subqueries](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subqueries-scalar-subqueries.md): Return a single value. A scalar subquery produces a one-row, one-column result that can be used anywhere a constant or expression is valid. - [Subquery Limitations](https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data/subqueries/subquery-limitations.md): Review restrictions on subquery usage. This page details unsupported operations, such as modifying a table while selecting from it in a subquery. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://mariadb.com/docs/server/reference/sql-statements/data-manipulation/selecting-data.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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