SelectQuery Class

A set of columns (from a single table or multiple joined tables) that forms a SELECT statement when executing a query.

Namespace: DevExpress.DataAccess.Sql

Assembly: DevExpress.DataAccess.v20.2.dll

Declaration

public sealed class SelectQuery :
    SqlQuery
Public NotInheritable Class SelectQuery
    Inherits SqlQuery

The following members accept/return SelectQuery objects:

Library Related API Members
Cross-Platform Class Library QueryBuilderInput.ResultQuery
SelectQueryFluentBuilder.Build(String)
ASP.NET Controls and MVC Extensions QueryBuilderSaveCallbackResult.ResultQuery
Reporting SaveQueryEventArgs.ResultQuery

Remarks

NOTE

Use the SelectQueryFluentBuilder class instead, to use a fluent syntax when constructing a SELECT statement.

In the following example, a query selects and orders records from a single data table.

using DevExpress.DataAccess.ConnectionParameters;
using DevExpress.DataAccess.Sql;
using System.ComponentModel;
// ... 

private SqlDataSource BindToData() {
    // Create a data source with the required connection parameters. 
    var connectionParameters = new Access97ConnectionParameters("../../Data/nwind.mdb", "", "");
    var ds = new SqlDataSource(connectionParameters);

    // Return a list of categories sorted by the number of products in each category.     
    var selectQuery = new SelectQuery("Products");
    var products = selectQuery.AddTable("Products");
    selectQuery.SelectColumn(products, "CategoryID");
    selectQuery.GroupBy(products, "CategoryID");
    selectQuery.SortBy(products, "ProductID", AggregationType.Count, ListSortDirection.Descending);
    selectQuery.FilterString = "[CategoryID] != 8";
    // Add the query to the collection and return the data source   
    ds.Queries.Add(selectQuery);
    ds.Fill();
    return ds;
}

In the following example, a query uses an inner join to select columns from separate data tables sharing a common column key.

using DevExpress.DataAccess.Sql;
using DevExpress.DataAccess.ConnectionParameters;
// ...

private SqlDataSource BindToData(){
    // Create a data source with the required connection parameters. 
    var connectionParameters = new Access97ConnectionParameters("../../Data/nwind.mdb", "", "");
    var ds = new SqlDataSource(connectionParameters);

    // Join the Categories and Products table by the CategoryID column. 
    // Return the list of categories and the number of products in each category. 
    // Sort the categories by the number of products in them. 
    // The included categories must contain a specific number of products.
    var selectQuery = new SelectQuery("Categories");
    var categories = selectQuery.AddTable("Categories");
    selectQuery.SelectColumn(categories, "CategoryName");
    selectQuery.GroupBy(categories, "CategoryName");
    var products = selectQuery.AddTable("Products");
    selectQuery.AddRelation(categories, products, "CategoryID");
    selectQuery.SelectColumn(products, "ProductName", AggregationType.Count, "ProductCount");
    selectQuery.SortBy(products, "ProductName", AggregationType.Count, System.ComponentModel.ListSortDirection.Descending);
    selectQuery.GroupFilterString = "[ProductCount] > 7";

    // Add the query to the collection and return the data source. 
    ds.Queries.Add(selectQuery);
    ds.Fill();
    return ds;
}

To execute all valid queries specified for a data source and obtain the result set, call the SqlDataSource.Fill method. To obtain the data source schema, call the SqlDataSource.RebuildResultSchema method.

You can register a custom aggregate function and use it in a SELECT query expression. For sample code, see the following example online: How to use a custom function in a query expression.

Inheritance

Object
SqlQuery
SelectQuery

Extension Methods

Show 20 items
See Also