SQL Functions and Joins Quiz

What does the MIN function do in SQL?

• Returns the maximum value

• Returns the minimum value

• Calculates the average value

• Counts the number of rows

Answer explanation

The MIN function in SQL is used to return the minimum value from a set of values in a specified column. Therefore, the correct answer is 'Returns the minimum value'.

Which SQL function would you use to find the total of a column?

• MIN

• COUNT

• SUM

• AVG

Answer explanation

The SUM function in SQL is specifically designed to calculate the total of a numeric column. Unlike MIN, COUNT, and AVG, which serve different purposes, SUM directly provides the total value of the specified column.

What is the result of the query SELECT COUNT(OrderID) FROM Orders?

• 2

• 5

• 4

• 3

Answer explanation

The query SELECT COUNT(OrderID) counts the number of entries in the Orders table. The correct answer is 4, indicating there are four orders recorded in the database.

What does the AVG function calculate?

• The total of all values

• The minimum value

• The average of a specified column

• The maximum value

Answer explanation

The AVG function calculates the average of a specified column by summing all the values in that column and dividing by the count of those values, making 'The average of a specified column' the correct choice.

Which SQL command is used to group results by one or more columns?

• HAVING

• JOIN

• GROUP BY

• ORDER BY

Answer explanation

The correct command to group results by one or more columns in SQL is 'GROUP BY'. This command aggregates data based on specified columns, allowing for summary statistics and organized results.

What is the purpose of the HAVING clause in SQL?

• To sort the results

• To join two tables

• To filter records after grouping

• To filter records before grouping

Answer explanation

The HAVING clause is used in SQL to filter records after they have been grouped by the GROUP BY clause. This allows for conditions to be applied to aggregated data, making it essential for refining results based on group calculations.

What does the YEAR function return?

• The current date

• The four-digit year

• The day of a date

• The month of a date

Answer explanation

The YEAR function extracts the four-digit year from a given date. Therefore, the correct answer is 'The four-digit year', as it specifically returns the year component, not the full date, day, or month.

What is the syntax for the GETDATE function?

• CURRENT_DATE();

• SELECT CURRENT_DATE;

• GETDATE();

• SELECT GETDATE();

Answer explanation

The correct syntax for using the GETDATE function in SQL is 'SELECT GETDATE();'. This retrieves the current date and time from the system. The other options are either incorrect or incomplete.

What does the DATEDIFF function do?

• Calculates the sum of two dates

• Returns the difference between two dates

• Adds a specified time to a date

• Returns the current date

Answer explanation

The DATEDIFF function specifically calculates the difference between two dates, returning the result in a specified unit (like days, months, or years). This makes 'Returns the difference between two dates' the correct choice.

Which function would you use to round a number to a specific number of decimal places?

• ABS

• ROUND

• CEILING

• FLOOR

Answer explanation

The ROUND function is specifically designed to round a number to a specified number of decimal places, making it the correct choice. ABS returns the absolute value, while CEILING and FLOOR round numbers in different ways.