.. _query_tool:

**************
The Query tool  
**************

The Query tool is a powerful, feature-rich environment that allows you to execute arbitrary SQL commands and review the result set.  If you access the Query tool via the *Query Tool* menu selection from the *Tools* menu, you can:

* Issue ad-hoc SQL queries. 
* Execute arbitrary SQL commands.
* Save the data displayed in the output panel to a CSV file. 
* Review the execution plan of a SQL statement in either a text or a graphical format.
* View analytical information about a SQL statement.

If you open the Query tool via the *View Data* context-menu selection, the Query tool acts as a data editor, allowing you to:  

* View or modify the data that is stored in a table. 
* Filter the result set.
* Save the data displayed in the output panel to a CSV file.
* Review the execution plan of a SQL statement in either a text or a graphical format.
* View analytical information about a SQL statement.

.. image:: images/query_tool.png

The Query tool features a toolbar with frequently used options, and a work environment divided into two panels: 

* The upper panel of the Query tool contains the *SQL Editor*.  You can use the panel to manually enter a query, or review the query that generated the result set displayed in the lower panel. 
* The lower panel of the Query tool contains the *Data Output* panel. The output panel displays the result of a query, or information about a query's execution plan.

pgAdmin allows you to open multiple copies of the Query tool (in individual tabs) simultaneously.  For example, if you select *Query tool* from the *Tools* menu, the Query tool opens in a tab labeled *Query-1*; if you open the Query tool again (without closing *Query-1*), a second copy will open in *Query-2*.  To close a copy of the Query tool, click the *X* in the upper-right hand corner of the tab bar.

**The Query tool Toolbar**

The *Query tool* toolbar uses context-sensitive icons that provide shortcuts to frequently performed tasks. If an icon is highlighted, the option is enabled; if the icon is grayed-out, the task is disabled. 

.. image:: images/query_toolbar.png 

Hover over an icon to display a tooltip that describes the icon's functionality.

+--------------------+---------------------------------------------------------------------------------------------------+
| Icon               | Behavior                                                                                          |
+====================+===================================================================================================+
| *Open File*        | Click the *Open File* icon to display the content of a saved data set or query in the             |
|                    | SQL Editor.                                                                                       |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Save*     	     | Click the *Save* icon to save the query that is currently displayed in the SQL Editor panel.      |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Copy*             | Click the *Copy* icon to copy the currently selected row.                                         |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Paste*            | Click the *Paste* icon to paste the content that is currently on the clipboard.                   |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Add New Row*      | Use the *Add New Row* icon to add a new row in the output panel.                                  |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Filter*           | Click the *Filter* icon to open a dialog that allows you to write and apply a filter for the      |
|                    | content currently displayed in the output panel.  Click the down arrow to open the *Filter* drop- |
|                    | down menu and select from pre-defined options:                                                    |
|                    |                                                                                                   |
|                    |  Select *Remove* to remove the currently applied filter and display the complete result set.      |
|                    |                                                                                                   |
|                    |  Select *By selection* to refresh the displayed data, displaying only those rows that have columns|
|                    |  that match the currently highlighted value.                                                      |
|                    |                                                                                                   |
|                    |  Select *Exclude selection* to refresh the displayed data, excluding those rows that have columns |
|                    |  that match the currently highlighted value.                                                      |
+--------------------+---------------------------------------------------------------------------------------------------+
| *No limit*         | Use the *No limit* drop-down listbox to specify how many rows to display in the output panel.     |
|                    |    Select from *No limit* (the default), *1000 rows*, *500 rows*, or *100 rows*.                  |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Execute/Refresh*  | Click the *Execute/Refresh* icon to either execute or refresh the query highlighted in the SQL    |
|                    | editor panel. Click the down arrow to access other execution options:                             |
|                    |                                                                                                   |
|                    |     Select *Explain* to view an explanation plan for the current query.  The result of the        |
|                    |     EXPLAIN is displayed graphically on the *Explain* tab of the output panel, and in text        |
|                    |     form on the *Data Output* tab.                                                                |
|                    |                                                                                                   |
|                    |     Select *Explain analyze* to invoke an EXPLAIN ANALYZE command on the current query.           |
|                    |                                                                                                   |
|                    |     Navigate through the *Explain Options* menu to select options for the EXPLAIN command:        |
|                    |                                                                                                   |
|                    |       Select *Verbose* to display additional information regarding the query plan.                |
|                    |                                                                                                   |
|                    |       Select *Costs* to include information on the estimated startup and total cost of each       |
|                    |       plan node, as well as the estimated number of rows and the estimated width of each          |
|                    |       row.                                                                                        |
|                    |                                                                                                   |
|                    |       Select *Buffers* to include information on buffer usage.                                    |
|                    |                                                                                                   |
|                    |       Select *Timing* to include information about the startup time and the amount of time        |
|                    |       spent in each node of the query.                                                            |
|                    |                                                                                                   |
|                    |    Add a check next to *Auto-Rollback* to instruct the server to automatically roll back a        |
|                    |    transaction if an error occurs during the transaction.                                         |
|                    |                                                                                                   |
|                    |    Add a check next to *Auto-Commit* to instruct the server to automatically commit each          |
|                    |    transaction.  Any changes made by the transaction will be visible to others, and               |
|                    |    durable in the event of a crash.                                                               |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Stop*             | Click the *Stop* icon to cancel the execution of the currently running query.                     |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Edit*             | Use options on the *Edit* drop-down menu to erase the contents of the query window or erase       |
|                    | the content of the *History* tab.                                                                 |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Download as CSV*  | Click the *Download as CSV* icon to download the result set of the current query to a             |
|                    | comma-separated list.                                                                             |
+--------------------+---------------------------------------------------------------------------------------------------+
| *Search*           | Use the *Search* field to search the result set for specific content.                             |
+--------------------+---------------------------------------------------------------------------------------------------+

**The SQL Editor Panel**

The *SQL editor* panel contains a workspace for entering commands; you can read a query from a file, or type a query. It features syntax coloring and autocompletion to help you write queries.
   
.. image:: images/query_sql_editor.png

To use autocomplete, start typing your query, and press the Control+Space shortcut to see a list of possible object names to insert. For example, type "\*SELECT \* FROM\* " (without the quotes, but with the trailing space), and then press the Control+Space key combination to select from a popup menu of autocomplete options. 

.. image:: images/query_autocomplete.png

After entering a query, select the *Execute/Refresh* icon from the toolbar. The complete contents of the SQL editor panel will be sent to the database server for execution. To execute a section of the code that is displayed in the SQL editor, highlight the text that you want the server to execute, and click the *Execute/Refresh* icon. 

.. image:: images/query_execute_section.png

The message returned by the server is displayed on the *Messages* tab of the output panel.  If the command is successful, the *Messages* tab displays execution details.

.. image:: images/query_tool_message.png

The editor also offers several features that help with code formatting:

* The auto-indent feature will automatically indent text to the same depth as the previous line when you press the Return key.
* Block indent text by selecting two or more lines and pressing the Tab key.
* Block outdent text that has been indented using the Shift+Tab key combination.
* Comment out SQL by selecting some text and pressing Control+K.
* Uncomment SQL by selecting some text starting with a comment and pressing Control+Shift+K.
* Shift the selected text to upper case by pressing Control+U.
* Shift the selected text to lower case by pressing Control+Shift+U.

**The Data Output Panel**

Use the *Data Output* panel of the *Query tool* to view data and information generated by a query in the *SQL editor*, or to *View Data* for an object currently selected in the *pgAdmin* tree control. 

The *Data Output* panel organizes output through the following tabs: *Data Output*, *Explain*, *Messages*, and *History*. 

.. image:: images/query_output_data.png

If the Query tool is opened through the *Query tool* menu option, you can use the *Data Output* tab to view the results of an arbitrary query in a table format. If the Query tool is opened through a *View Data* menu option, you can use the *Data Output* tab to review the data stored in the selected table.

* Click a column header to sort data by that column. Click again to reverse the sorting order.
* If enabled, use the *Filter* options from the Query tool toolbar to refine the result set displayed on the *Data Output* tab.
* If enabled, use the *No limit* drop-down to specify how many rows to display on the *Data Output* tab.
* If enabled, use the *Execute/Refresh* options to retrieve query execution information and set query execution options.
* Use the *Download as CSV* icon to download the content of the *Data Output* tab as a comma-delimited file.

All rowsets from previous queries or commands that are displayed in the *Data Output* panel will be discarded when you invoke another query; open another query tool from the menu bar or context-menu to keep results available.

Use the *Explain* tab to view a graphical representation of a query: 

.. image:: images/query_output_explain.png

To generate a graphical explain diagram, navigate to the *Explain* tab, and select *Explain*, *Explain Analyze*, or one or more options from the *Explain options* menu on the *Execute/Refresh* drop-down. Please note that *EXPLAIN VERBOSE* cannot be displayed graphically. Hover over an icon on the *Explain* tab to review information about that item; a popup window will display information about the selected object: 

.. image:: images/query_output_explain_details.png

Note that the *QUERY PLAN* that accompanies the *Explain analyze* is available in the *Data Output* tab. 

Use the *Messages* tab to view information about the last-executed query; if the server returns an error, the error message will be displayed on the *Messages* tab: 

.. image:: images/query_output_error.png

If a query succeeds, the *Messages* tab displays how long the query took to complete and how many rows were retrieved: 

.. image:: images/query_output_messages.png

Use the *History* tab to review activity for the current session:

.. image:: images/query_output_history.png
   
To erase the content of the *History* tab, select *Clear history* from the *Edit* drop-down menu.