Updating data from one table to another

Otherwise,you might specify the additional search criteria in a way that produces incorrect results.

Rows in the source are matched with rows in the target based on the join predicate specified in the ON clause. One insert, update, or delete operation is performed per input row.

However, in this section you won't need them to solve the problem of updating a join, because in ADO, joins are naturally updatable.

For example, should the insert of a row into the previous join result in a new product and also a new supplier, or just a new product?

The Client Data Set/Provider architecture allows you to specify a primary update table (and advanced features actually not covered in the book) and also customize the updates' SQL, as we partially saw in Chapter 14 and we'll further explore in Chapter 16, "Multitier Data Snap Applications." ADO supports an equivalent to cached updates called batch updates, which are similar to the BDE approach.

Depending on the WHEN clauses specified in the statement, the input row might be any one of the following: The combination of WHEN clauses specified in the MERGE statement determines the join type that is implemented by the query processor and affects the resulting input stream.

To illustrate, consider the following example source and target tables and data. Target(Employee ID int, Employee Name varchar(10), CONSTRAINT Target_PK PRIMARY KEY(Employee ID)); CREATE TABLE dbo.

Search for updating data from one table to another:

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Properties class Program Data Adapters and Data Readers Row States and Row Versions Accept Changes and Reject Changes Merging Data Set Contents Retrieving Identity or Autonumber Values ADO.

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