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This document describes the Query Builder and consists of the following sections:
- Query Builder Overview
- Run the Query Builder
- Select Tables
- Join Tables
- Edit Parameters
- Filter Data
- Shape Data
- Enable Custom SQL Editing
- Preview Results
Query Builder Overview
The Query Builder provides a visual interface for constructing SQL queries used to access an SqlDataSource's tables and views.
The following DevExpress products use the Query Builder for binding to data:
Run the Query Builder
Another version of the query customization page appears when you use the Report Wizard to bind reports to data. In this case, click the button in the Queries category to create a new query using the Query Builder.
Use the following SqlDataSourceUIHelper class methods to invoke the Query Builder in your WinForms application in a standalone mode:
See How to use the Query Builder in a WinForms application for a sample code.
You can add a specific data table or view to a query by dragging the corresponding item from the list of available tables and dropping it onto the list of data tables to be used.
Enable check boxes for the table fields that you want to include in the query result set.
Each table provides the context menu, which allows you to rename the table or remove it from the query.
Click the list of available tables on the left and press CTRL+F to search for a specific table or view.
You can join multiple tables within the same query. The Query Builder automatically highlights tables related to any of the previously added tables. Drag-and-drop a subordinate table in the same way you added a main table to include it in a query and automatically create an inner join relation based on a key column.
Alternatively, you can join tables by clicking the plus button in a row corresponding to a key column.
You can customize the relationship by right-clicking it on the diagram and selecting Edit Relation in the invoked context menu. Use the Join Editor to select the join type (Left Outer or Inner), apply a logical operator (Equals to, Is less than, etc.) and column key fields.
A left outer join returns an inner join's values, along with all the values in the "left" table that do not match the "right" table, including rows with NULL (empty) values in the key field.
When the left outer join is selected, the relationship line displays an arrow pointing to the "right" table.
You can manually join tables if they do not have a relationship at the database level. In this case, when you drag-and-drop a table onto the list of tables, the Join Editor is automatically invoked allowing you to construct a custom join relationship.
After executing the query, it returns a "flat" table composed of data records selected based on the specified join options.
Click the Edit Parameters button to invoke the Query Parameters dialog, which allows you to add and remove query parameters as well as specify parameter settings.
The following properties are available for each query parameter:
- Name - specifies the name used to refer to a parameter.
- Type - specifies the parameter value's data type.
- Expression - determines whether the actual parameter value is static or generated dynamically.
- Value - specifies a query parameter's actual value. If the Expression option is enabled, the actual parameter value is produced dynamically by calculating an associated expression.
You can then access the created parameters on the Configure Query Parameters wizard page.
Click the Filter... button in the Query Builder to specify filter criteria. This invokes the Filter Editor, which provides the following capabilities:
The editor contains the Filter tab that allows you to specify the resulting data's filter conditions. You can also use query parameters in filter criteria.
Group Filter Tab
The Group Filter tab allows you to specify filter conditions for grouped and aggregated data. This tab is disabled if data is not grouped.
This editor allows you to limit the number of resulting data rows. When data is sorted, you can specify how many rows to skip before retrieving the specified number of rows.
The skip setting cannot be considered for specific data providers .
Another option allows you to include only distinct values into the resulting set.
The Query Builder displays the column list under the data source editor, which provides various shaping options:
Specifies the selected column.
You can choose a column from the drop-down list or create a column expression by clicking the corresponding column's ellipsis button.
Specifies the table containing the selected column.
This option indicates (All Tables) if you created an expression for the corresponding column.
Specifies a custom column name (alias).
This option is available only for columns that you included in a query.
Specifies whether to include the column in the query's resulting set.
Specifies whether to preserve the original data record order within the column or sort them (ascending or descending).
When binding to XML files, the Query Builder does not support sorting by aggregate functions, DISTINCT and SELECT ALL statements, and custom SQL.
This option becomes available after applying sorting to the data column records.
It defines the priority in which sorting is applied to multiple columns (a lower number has a higher priority).
For example, if column A has the sort order set to 1 and column B has it set to 2, the query is first sorted by column A and then by the column B.
Changing this setting for one column automatically updates other columns' sorting order to avoid conflicting priorities.
Specifies whether to group the query's resulting set by this column.
Specifies whether to aggregate the column's data records.
The following aggregate functions are supported:
Applying any of these functions to a column discards individual data records from the query result set, which only includes the aggregate function result.
You should apply aggregation/grouping to either all columns or none of them.
Enable Custom SQL Editing
Enable the Allow Edit SQL option to customize an SQL string manually. Switching to this mode disables the Query Builder's visual features in favor of the specified SQL string value.
In the End-User Report Designers, manual SQL query editing is considered unsafe and is disabled by default. See the following documents for more information:
Custom SQL queries are validated before their execution. Although the default validation mechanism only allows custom queries containing SELECT statements (except for SELECT INTO clauses), it is not safe because it does not prevent the execution of potentially harmful requests. We recommend implementing a validation logic that permits only execution of specific query kinds. See the Providing Custom Query Validation in Report Designer document for more information.
You can preview the query execution's result in a tabular form by clicking the Preview Results button.
This opens the Data Preview window displaying the query result set (limited to the first 1000 data records).