True or False: SQL query runs in memory Unique key can have null values . Foreig
ID: 3671062 • Letter: T
Question
True or False:
SQL query runs in memory
Unique key can have null values .
Foreign keys can have duplicate values .
Instance recovery is performed after a power failure when the database is brought up.
Export/import utility is for backing up the database datafiles.
Excessive commits can harm the database performance .
Rollback will undo the last committed transaction.
In correlated sub query the outer query is dependent on the inner query.
PL/SQL is the structured query language for MS SqL server.
Users can’t use the database during cold backup.
Explanation / Answer
1. Yes, when you execute query all the relevant information/data is loaded in memory for the execution of query
2. Yes , it is posiible but only in one row . In other words, you can have Unique Constraint on column that contain NULL but it's limited to a single row can have NULL value
3. Yes, unless it's a unique contraint or somehow linked to unique index
4. Yes , could be
5. No , It is to quickly get data into the database or take it out of the database ,if required
6. In simple YES , because system has to spend lot of time to do log file sync . But that's not the case always because lot of commit reduction will create more redo generation and transformed into the log buffer space problem. Right balance is required so that database’s transactional integrity must be maintened .
7. Yes , Basically ROLLBACK is inverse of COMMIT statement and undo some or all of changes made to the database while executing current transaction.
8. No , it's other way arround , for every value of outer query , sub-query/inner query gets executed
9. NO. PL/SQL is available in oracle databases
10 YES , also called as offline backup, backup of database when it is offline and not available for any update
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