D492 Data Analytics Applications - Set 1 - Part 3

Correct Answer: LIMIT

The LIMIT clause is used to specify the number of rows to return from the result set. SELECT retrieves data, ORDER BY sorts the result set, and GROUP BY groups rows based on column values.

Correct Answer: To improve the performance of queries

An index in SQL is used to improve the performance of queries by allowing the database to find rows more quickly. It does not store data or create new tables but enhances the efficiency of data retrieval.

Correct Answer: YEAR()

The YEAR() function extracts the year from a date. DATE() is used to format a date, EXTRACT() extracts parts of a date but requires specifying the unit, and SUBSTRING() extracts portions of a string.

Correct Answer: Hash table

A hash table is commonly used for fast data lookup in databases due to its ability to map keys to values efficiently. Linked lists, stacks, and queues are used for different purposes and do not provide the same efficiency for lookups.

Correct Answer: To add, modify, or delete columns in an existing table

The ALTER statement is used to modify the structure of an existing table, including adding, modifying, or deleting columns. INSERT adds data, DROP removes tables, and SELECT retrieves data.

Correct Answer: To filter groups of rows after aggregation

The HAVING clause is used to filter groups of rows after they have been aggregated, often used with GROUP BY. WHERE is used to filter rows before aggregation, DISTINCT filters duplicates, and JOIN combines rows from multiple tables.

Correct Answer: LIKE

The LIKE operator is used to select rows that match a specified pattern. BETWEEN selects values within a range, IN checks if a value is in a list, and EXISTS checks if a subquery returns any rows.

Correct Answer: To remove a table or database

The DROP command is used to remove a table or database from the system. It completely deletes the structure, unlike DELETE, which removes data but retains the table.

Correct Answer: UNION

The UNION statement is used to combine the result sets of two or more SELECT statements, removing duplicates by default. JOIN combines rows from tables, GROUP BY groups rows, and ORDER BY sorts the result set.

Correct Answer: To uniquely identify each row in a table

The PRIMARY KEY uniquely identifies each row in a table and ensures that no duplicate values exist. It is crucial for maintaining data integrity, while foreign keys link tables, and sorting is handled by ORDER BY.