tailieunhanh - Microsoft ADO .NET 4 Step by Step - p 28

Để sử dụng các bản đồ chi tiết của bảng điều khiển, chọn một tổ chức từ bề mặt thiết kế trực quan. bảng điều khiển hiển thị tất cả các cột ánh xạ đã được xác định cho thực thể, với tính chất mô hình lưu trữ trên một nửa trái và mô hình khái niệm tài sản bên phải của họ. | 246 Microsoft 4 Step by Step Getting to Know Entity SQL Entity SQL is based in part on the T-SQL imperative query language found in Microsoft s SQL Server product. Despite this lineage there are some significant differences between T-SQL and Entity SQL Entity SQL is a selection-only language. Whereas T-SQL includes support for data manipulation language DML and data definition language DDL Entity SQL supports only data retrieval. The focus is on the SELECT statement INSERT UPDATE and DELETE are not available. When updates are needed the standard Entity Framework tools take over. None of the batch query or stored procedure functionality found in T-SQL is available in Entity SQL. Entity SQL does include support for custom functions but they exist only to augment a related SELECT statement. T-SQL focuses on the logical tables and rows in the database. Even when an Entity Framework model targets a SQL Server database Entity SQL queries focus on the data as expressed through the conceptual model. Writing Basic Queries Entity SQL selection queries follow the same general syntax as those of standard SQL with SELECT FROM WHERE GROUP BY and ORDER BY clauses. SELECT list-of-fields FROM one-or-more-tables WHERE Boolean-expression GROUP BY aggregate-grouping-fields ORDER BY sort-by-fields As with standard SQL all fields included anywhere within the query must tie back to a table or entity that is specified in the FROM clause or in a subquery. The FROM clause usually lists its sources from the available entities in the model that is to the entity collections that themselves contain individual entities. These entity collections commonly use pluralized names. -- This is probably not correct SELECT . FROM Customer -- But this is valid with its pluralized name SELECT . FROM Customers Chapter 15 Querying Data in the Framework 247 The SELECT clause is a comma-delimited list of the values to be returned in each result row. In Entity SQL every reference to a field value or .