d492 Data Analytics Applications - Set 3 - Part 1

Correct Answer: SELECT *

The SELECT * statement is used to retrieve all columns from a table. SELECT DISTINCT eliminates duplicates, while SELECT ALL and SELECT COLUMNS are not valid SQL statements for this purpose.

Correct Answer: Deletes specific rows from a table

The DELETE statement is used to remove specific rows from a table based on a condition. DROP is used to delete an entire table or database, and ALTER modifies the structure of a table.

Correct Answer: To select specific columns from a table

The PROJECT operation in relational algebra is used to select specific columns from a table, eliminating the others. SELECT chooses rows, while JOIN combines rows from two tables.

Correct Answer: GROUP BY

The GROUP BY clause is used to group the result set by one or more columns, often in conjunction with aggregate functions. ORDER BY sorts the result, WHERE filters rows, and HAVING filters groups after aggregation.

Correct Answer: To link rows between two tables

A FOREIGN KEY is used to link rows between two tables by referencing a primary key in another table. It does not ensure uniqueness or speed up retrieval.

Correct Answer: Deletes all rows from a table but retains the structure

The TRUNCATE statement removes all rows from a table, but the table structure remains intact. DELETE can remove specific rows, and DROP deletes the entire table.

Correct Answer: CONCAT()

The CONCAT() function is used to concatenate two or more strings in SQL. SUBSTRING() extracts part of a string, LENGTH() returns the length of a string, and TRIM() removes leading and trailing spaces.

Correct Answer: UNION

The UNION operation returns all rows from two tables, including rows that appear in both tables. INTERSECT returns only rows common to both tables, JOIN combines rows based on a condition, and PRODUCT returns all possible combinations of rows from two tables.

Correct Answer: WHERE

The WHERE clause is used to filter rows based on a specified condition. GROUP BY groups rows, ORDER BY sorts rows, and DISTINCT removes duplicates from the result set.

Correct Answer: ROUND()

The ROUND() function is used to round a number to a specified number of decimal places. POW() raises a number to a power, SQRT() returns the square root, and ABS() returns the absolute value.

Correct Answer: To filter groups after aggregation

The HAVING clause is used to filter groups of rows after aggregation, often used with GROUP BY. WHERE filters rows before aggregation, ORDER BY sorts rows, and DISTINCT removes duplicates.

Correct Answer: Limits the number of rows returned

The LIMIT clause is used to specify the maximum number of rows to return in a result set. It does not limit columns, tables, or conditions.

Correct Answer: LENGTH()

The LENGTH() function returns the number of characters in a string. CONCAT() joins strings, TRIM() removes spaces, and SUBSTRING() extracts part of a string.

Correct Answer: FULL JOIN

A FULL JOIN returns all rows from both tables, with NULLs for non-matching rows. INNER JOIN returns only matching rows, while LEFT JOIN and RIGHT JOIN return all rows from one table and matching rows from the other.

Correct Answer: Checks if a subquery returns any rows

The EXISTS operator returns TRUE if a subquery returns one or more rows. It is often used to check for the existence of certain records within a subquery.

Correct Answer: To combine the result sets of two queries, removing duplicates

The UNION operator combines the result sets of two queries and removes any duplicate rows. If duplicates should be included, the UNION ALL operator is used.

Correct Answer: ORDER BY DESC

The ORDER BY DESC clause is used to sort the result set in descending order. GROUP BY groups rows, WHERE filters rows, and DISTINCT removes duplicates.

Correct Answer: To uniquely identify each row in a table

A PRIMARY KEY uniquely identifies each row in a table and ensures that no duplicate values exist. It is used to maintain data integrity.

Correct Answer: GROUP BY

The GROUP BY clause groups rows that have the same values in specified columns, often used with aggregate functions. ORDER BY sorts rows, WHERE filters rows, and HAVING filters groups after aggregation.

Correct Answer: Selects rows within a specified range of values

The BETWEEN operator selects rows with values within a specified range, including the boundary values. It is commonly used with numeric or date values.