markdown/query/query.html.md.erb

---
title: Querying Data
---

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This topic provides information about using SQL in HAWQ databases.

You enter SQL statements called queries to view and analyze data in a database using the `psql` interactive SQL client and other client tools.

**Note:** HAWQ queries timeout after a period of 600 seconds. For this reason, long-running queries may appear to hang until results are processed or until the timeout period expires.

-   **[About HAWQ Query Processing](../query/HAWQQueryProcessing.html)**

    This topic provides an overview of how HAWQ processes queries. Understanding this process can be useful when writing and tuning queries.

-   **[About GPORCA](../query/gporca/query-gporca-optimizer.html)**

    In HAWQ, you can use GPORCA or the legacy query optimizer.

-   **[Defining Queries](../query/defining-queries.html)**

    HAWQ is based on the PostgreSQL implementation of the SQL standard. SQL commands are typically entered using the standard PostgreSQL interactive terminal `psql`, but other programs that have similar functionality can be used as well.

-   **[Using Functions and Operators](../query/functions-operators.html)**

    HAWQ evaluates functions and operators used in SQL expressions.

-   **[Query Performance](../query/query-performance.html)**

    HAWQ dynamically allocates resources to queries. Query performance depends on several factors such as data locality, number of virtual segments used for the query and general cluster health.

-   **[Query Profiling](../query/query-profiling.html)**

    Examine the query plans of poorly performing queries to identify possible performance tuning opportunities.