A function called from SQL statements must obey certain rules meant to control side effects. XXX Employee Fetched: Idea taken from Oracle Community Forum Post. Example 1: In this example, we will project all the employee name from emp table using a cursor-FOR loop.
Declare a record based on the row of data returned by the query. If the statement fails, Oracle rolls back to the savepoint. If you try to exit an active autonomous transaction without committing or rolling back, Oracle raises an exception.
Use an explicit cursor when you are fetching multiple rows but might conditionally exit before all rows are fetched. The function picks the appropriate SELECT statement, opens the cursor variable for that statement, and then returns the variable pointing to that result set.
You give the cursor a name and associate it with a specific query. Savepoints defined in the main transaction are unrelated to savepoints defined in its autonomous transactions.
It is still, however, a good idea to explicitly close the cursor yourself. So even though your code looks as if you are fetching one row at a time, Oracle Database will actually fetch 100 rows at a time—and enable you to work with each row individually.
When the cursor is declared in a declaration section and not in a package , Oracle Database will also automatically close it when the block in which it is declared terminates. Selecting At Most One Row: A nested transaction's committed changes are not visible to other transactions until the main transaction commits.
Read-only transactions are useful for running multiple queries while other users update the same tables. Book List. Unlike with an explicit cursor, you can pass a cursor variable as an argument to a procedure or a function.
The rows are unlocked when you commit or roll back the transaction. Example 6-5 shows how to generate a new sequence number and refer to that same number in more than one statement. Rahul Rahul 62. Skip Headers. The following example, retrieves columns from a cursor into a collection:.
Implicit Cursor Explicit Cursor Implicit Cursor Whenever any DML operations occur in the database, an implicit cursor is created that holds the rows affected, in that particular operation. Code Listing 2: For each row in the table, the correlated subquery computes the average salary for the corresponding department.