#Cursors sql driver#
Each time a client application calls an API cursor function, the SQL Server Native Client ODBC driver or the ADO DLL performs the cursor operation on the result set rows cached on the client. Client cursors are implemented by caching all the result set rows on the client. Client cursorsĬlient cursors are implemented internally by the SQL Server Native Client ODBC driver and by the DLL that implements the ADO API. Each time a client application calls an API cursor function, the SQL Server Native Client OLE DB provider or ODBC driver transmits the request to the server for action against the API server cursor.
API server cursors are implemented on the server. Application programming interface (API) server cursorsĪPI cursors support the API cursor functions in OLE DB and ODBC. They may also be contained in batches, stored procedures, or triggers. Transact-SQL cursors are implemented on the server and are managed by Transact-SQL statements sent from the client to the server. Transact-SQL cursors are based on the DECLARE CURSOR syntax and used mainly in Transact-SQL scripts, stored procedures, and triggers. SQL Server supports three cursor implementations.
#Cursors sql update#
When that is the case, if there is no requirement to update tables based on the cursor, then use firehose cursors, meaning fast-forward and read-only cursors. However, there are scenarios where cursors are not only unavoidable, they are actually needed. In some scenarios, if there is a primary key on a table, a WHILE loop can be used instead of a cursor, without incurring in the overhead of a cursor. Providing Transact-SQL statements in scripts, stored procedures, and triggers access to the data in a result set. Supporting different levels of visibility to changes made by other users to the database data that is presented in the result set. Supporting data modifications to the rows at the current position in the result set. Retrieving one row or block of rows from the current position in the result set. Cursors are an extension to result sets that provide that mechanism.Īllowing positioning at specific rows of the result set. These applications need a mechanism to work with one row or a small block of rows at a time. Applications, especially interactive online applications, cannot always work effectively with the entire result set as a unit. This complete set of rows returned by the statement is known as the result set.
For example, the set of rows returned by a SELECT statement consists of all the rows that satisfy the conditions in the WHERE clause of the statement. Operations in a relational database act on a complete set of rows. Applies to: SQL Server (all supported versions) Azure SQL Database
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