Data Shaping Technology-providers required for Data configuration

Source: Internet
Author: User
Tags join ole
Generally, two providers are required for data configuration. The data configuration service of the service provider ole db provides the data configuration function, and the data provider, such as the ole db provider of SQL Server, provides the data rows that are filled with the Recordset.
The name of the service Provider can be specified as the value of the Provider attribute of the Connection object, or the Connection string keyword "Provider = ".
The name of the Data Provider can be specified as the value of the "Data Provider" dynamic attribute, which is added to the Properties set of the Connection object by Data Shaping Service for ole db. Alternatively, you can specify the connection string keyword "Data Provider = ".
If Recordset is not filled (for example, if all columns in The Recordset are created using the NEW keyword), no data provider is required. In this case, specify "Data Provider = none ".
Example
Dim cnn As New ADODB. Connection
Cnn. Provider = "MSDataShape"
Cnn. Open "Data Provider = MSDASQL; DSN = vfox; uid = sa; pwd = vfox; database = pubs"
Conventional Shape command
"Data configuration" defines the relationship between the columns that form the Recordset, the entries represented by the columns, and the way data is filled to the Recordset.
The formed Recordset can be composed of the following types of columns:
Column type description
The Recordset Field returned by the query command for the data provider, table, or previously formed Recordset.
The reference of a subset to another Recordset is called a "subset ". A subset column makes it possible to define a "parent-child" relationship. In this relationship, "parent" is a Recordset that contains a subset column, and "child" is a Recordset represented by a subset.
The value of the aggregate column is obtained by executing the "aggregate function" on all rows, or the column of all rows in the subrecordset. (See aggregate functions in the following table .)
The value of the calculated expression column is obtained by calculating the Visual Basic for Applications expression for the column in the same row of the Recordset. The expression is a parameter of the CALC function. (See the calculation expressions in the following table .)
Create an empty or fictitious field and fill in the data later. Columns are defined using the NEW keyword. (See the NEW keyword in the following table .)
The Shape command can contain a clause to specify the query command for the basic data provider and return the Recordset object. The query syntax depends on the requirements for basic data providers. Although ADO does not require any specified query language, it usually uses a Structured Query Language (SQL ).
You can use the SQL JOIN clause to associate two tables. However, the hierarchical Recordset can more effectively express information. Each row of the Recordset created by the JOIN operation repeats the information in a table. Among multiple sub-Recordset objects of hierarchical Recordset, each object has only one parent Recordset.

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