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Transaction Control
The Oracle is transaction oriented; that is, Oracle uses the transactions to make sure the data integrity. The transaction is a sequence of SQL data manipulation statements that does a logical unit of work. For illustration, the two UPDATE statements might credit one bank account and debit another.
At the same time, the Oracle makes permanent or undoes all the database changes made by a transaction. If your program fails in the middle of the transaction, the Oracle detects the error and rolls back the transaction. Therefore, the database is restored to its previous state automatically.
You use the ROLLBACK, COMMIT, SAVEPOINT, & SET TRANSACTION commands to control the transactions. The COMMIT makes everlasting and any database changes made during the present transaction. The ROLLBACK ends the present transaction and undoes any changes made as the transaction began. The SAVEPOINT marks the present point in the processing of a transaction. Used with the ROLLBACK, SAVEPOINT undoes part of a transaction. The SET TRANSACTION sets the transaction properties like the read/write access and isolation level.
Controlling Autonomous Transactions The first SQL statement in an autonomous routine starts a transaction. Whenever one transaction ends, the next SQL statement starts the oth
Committing and Rolling Back The COMMIT and ROLLBACK end the active autonomous transaction but do not exit the autonomous routine. As the figure shows, if one transaction ends,
UNION ALL - SQL Further varieties of UNION arise when we replace the key word DISTINCT by ALL in any of the foregoing examples, as in Example. ALL specifies that if row r appe
FETCH Statement The FETCH statement retrieve rows of data one at a time from the result set of the multi-row query. The data is stored in fields or variables which correspond t
Effects of NULL for Table Expression Here's an important distinction between expressions denoting tables and expressions denoting multisets of rows: a table expression cannot
Functions The function is a subprogram that calculates a value. The Functions and procedures are structured similar, except that the functions have a RETURN clause. You can
Parameter and Keyword Description: package_name: This construct identifies the package. AUTHID Clause: This determine whether all the packaged subprograms impleme
Deriving Predicates from Predicates in SQL The corresponding section in the theory book describes how predicates can be derived from predicates using (a) the logical connectiv
Loop Labels Like the PL/SQL blocks, loops can also be labeled. The label, an undeclared identifier enclosed by double angle brackets, should appear at the beginning of the LOOP
Data Abstraction The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to reme
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