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.v21.2.dll

Declaration

public sealed class SelectQuery :
    SqlQuery

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.

The following code snippets (auto-collected from DevExpress Examples) contain references to the SelectQuery class.

Note

The algorithm used to collect these code examples remains a work in progress. Accordingly, the links and snippets below may produce inaccurate results. If you encounter an issue with code examples below, please use the feedback form on this page to report the issue.

Inheritance

Object
SqlQuery
SelectQuery

Extension Methods

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See Also