УПР 31-60

What is the purpose of a foreign key in a relational database?

• To increase query speed

• To enforce referential integrity between tables

• To store unique values only

• To generate primary keys automatically

Which postgresql command is used to permanently delete a table and all its data?

• DROP TABLE table_name;

• DELETE FROM table_name;

• REMOVE TABLE table_name;

• TRUNCATE TABLE table_name;

You need to update multiple rows in a postgresql table at once Which SQL statement should you use?

• ALTER TABLE

• INSERT INTO

• UPDATE table_name SET column_name = value WHERE condition

• MODIFY TABLE

What is the function of the GROUP BY clause in SQL?

• It groups rows with the same values in specified columns for aggregate functions

• It filters results based on a given condition

• It sorts records in descending order

• It creates a backup of grouped rows

How can you prevent duplicate records in a postgresql table column?

• By using a FOREIGN KEY constraint

• By enabling indexing on the column

• By defining the column as UNIQUE

• By using the AUTO_INCREMENT property

What is a key difference between the DELETE and TRUNCATE commands in postgresql?

• DELETE allows filtering with WHERE, while TRUNCATE removes all rows instantly

• TRUNCATE removes specific rows based on conditions

• DELETE is faster than TRUNCATE

• TRUNCATE locks the database permanently

Which SQL function is used to return the number of rows in a table?

• SUM()

• AVG()

• COUNT()

• LENGTH()

You want to combine results from two SELECT queries but remove duplicate rows Which SQL clause should you use?

• JOIN

• UNION

• MERGE

• INTERSECT

What is the main advantage of using transactions in postgresql?

• It increases storage space

• It improves indexing speed

• It ensures data consistency by allowing rollback in case of failure

• It allows tables to be dropped more quickly

How does the SERIAL data type help in postgresql tables?

• It automatically generates unique integer values for a column

• It stores serial numbers as text

• It enables foreign key constraints

• It encrypts numerical data for security