Which of the following commands cannot be rolled back? Each correct answer represents a
complete solution. Choose two.
A.
DELETE
B.
TRUNCATE
C.
UPDATE
D.
COMMIT
Explanation:
COMMIT statement is a transaction control statement that ends the current database transaction
and makes all changes made in that
transaction permanent. It also releases all locks on the transaction.
The TRUNCATE statement is a Data Definition Language (DDL) statement that is used to remove all
records from a table. It also releases the
storage space used by the table. The TRUNCATE statement cannot be rolled back.
Syntax:
TRUNCATE TABLE TableName;
Therefore, both the commands, COMMIT and TRUNCATE, can never be rolled back.
Note: The TRUNCATE command includes a built-in COMMIT command.
Answer C and A are incorrect. The SQL UPDATE statement allows a user to update the current
values in a database with new values.
It contains three main clauses. The first clause specifies the table that requires an update, the
second clause specifies the column name and
the data values that will be inserted in place of the current values, and the third clause specifies the
criteria for the records that will be
updated. An example query is given below:
Update Employee{first clause}
Set Fname=”Roger”{second clause}
Lname=”Pressman”WHERE Empid=1{third clause}
The DELETE statement is a Data Manipulation Language (DML) statement that is used to delete
records from a table, based on the condition
specified in the WHERE clause. If the WHERE clause is omitted, all records in the table are deleted.
The DELETE statement can be rolled back.
Syntax:
DELETE [FROM] TableName
[WHERE condition];
The above two DML commands can therefore be rolled back.