Oracle SQL Oracle SQL DML Operations 3

Question 1

What is the purpose of the FOR UPDATE clause in an Oracle SQL SELECT statement?

Accepted Answer

Locks selected rows to prevent other sessions from modifying them

Answer

Automatically updates retrieved rows

Answer

Returns only updatable rows

Answer

Validates rows before update

Question 2

In Oracle SQL, which aggregate function is NOT ignored on NULL values?

Accepted Answer

COUNT(*)

Answer

SUM

Answer

AVG

Answer

MAX

Question 3

What does the NOWAIT option in SELECT ... FOR UPDATE NOWAIT do in Oracle SQL?

Accepted Answer

Returns an error immediately if rows are already locked

Answer

Skips the lock entirely

Answer

Waits indefinitely for the lock

Answer

Locks rows in read-only mode

Question 4

Which Oracle SQL UPDATE syntax uses a subquery to update multiple columns at once?

Accepted Answer

UPDATE t SET (col1,col2) = (SELECT v1,v2 FROM src WHERE ...)

Answer

UPDATE t SET col1,col2 FROM (SELECT ...)

Answer

UPDATE t COLUMNS (col1,col2) VALUES (SELECT ...)

Answer

UPDATE t SELECT col1=v1, col2=v2 FROM src

Question 5

What is the effect of omitting the WHERE clause in an Oracle SQL UPDATE statement?

Accepted Answer

All rows in the table are updated

Answer

The statement fails with an error

Answer

Only the first row is updated

Answer

No rows are updated

Question 6

Which Oracle SQL feature enables you to see the data in a table as it existed at a past point in time?

Accepted Answer

Flashback Query (AS OF TIMESTAMP)

Answer

ROLLBACK AS OF

Answer

TIME TRAVEL SELECT

Answer

RESTORE SELECT