Advanced SQL Aggregation Quiz

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Questions and Answers

Which function is used to perform calculations on multiple rows of a single column and return a single value?

  • FORMAT()
  • UCASE()
  • AVG() (correct)
  • MID()

Which function is used to count the number of rows in a database table, considering duplicates and Null?

  • NOW()
  • FIRST()
  • COUNT(*) (correct)
  • ROUND()

Which type of function is UCASE()?

  • Scalar function (correct)
  • Aggregate function
  • Non-existent function
  • COUNT(*) function

Which function is used to find the maximum value in a column?

<p>MAX() (B)</p> Signup and view all the answers

Which function is used to summarize the data in SQL?

<p>Aggregate functions (B)</p> Signup and view all the answers

  1. What is the purpose of SQL aggregate functions?

<p>SQL aggregate functions are used to perform calculations on multiple rows of a single column of a table and return a single value. They are also used to summarize the data.</p> Signup and view all the answers

  1. What is the syntax for the COUNT function in SQL? Provide an example.

<p>The syntax for the COUNT function is COUNT(<em>) or COUNT( [ALL|DISTINCT] expression ). An example of using COUNT(</em>) is COUNT(*), which returns the count of all the rows in a specified table, considering duplicates and Null.</p> Signup and view all the answers

  1. Name two scalar functions in SQL and briefly explain their purpose.

<p>Two scalar functions in SQL are UCASE() and ROUND(). UCASE() is used to convert a string to uppercase, while ROUND() is used to round a numeric field to the number of decimals specified.</p> Signup and view all the answers

  1. What does the COUNT function in SQL do when used with COUNT(*)?

<p>When used with COUNT(*), the COUNT function returns the count of all the rows in a specified table, considering duplicates and Null.</p> Signup and view all the answers

  1. How are aggregate functions different from scalar functions in SQL?

<p>Aggregate functions are used to perform operations from the values of a column and return a single value, while scalar functions are based on user input and also return a single value.</p> Signup and view all the answers

What is the syntax for the AVG() function in SQL? Provide an example.

<p>The syntax for the AVG() function in SQL is AVG(column_name). For example, AVG(salary) will calculate the average salary from the 'salary' column.</p> Signup and view all the answers

How does the COUNT function differ when using COUNT(*) versus COUNT(expression) in SQL?

<p>The COUNT(*) function returns the count of all rows in a specified table, considering duplicates and Null. The COUNT(expression) function returns the count of non-null values in the specified column.</p> Signup and view all the answers

Explain the purpose of the MAX() function in SQL with an example.

<p>The MAX() function in SQL is used to find the maximum value in a column. For example, MAX(price) will return the highest price from the 'price' column.</p> Signup and view all the answers

What is the purpose of the UCASE() function in SQL? Provide an example.

<p>The UCASE() function is used to convert a string to uppercase. For example, UCASE('hello') will return 'HELLO'.</p> Signup and view all the answers

How does the SUM() function differ from the AVG() function in SQL?

<p>The SUM() function is used to calculate the sum of values in a column, while the AVG() function calculates the average of values in a column.</p> Signup and view all the answers

What is the purpose of SQL aggregate functions?

<p>The purpose of SQL aggregate functions is to perform calculations on multiple rows of a single column and return a single value.</p> Signup and view all the answers

Which type of function is UCASE()?

<p>UCASE() is a scalar function in SQL.</p> Signup and view all the answers

Which function is used to count the number of rows in a database table, considering duplicates and Null?

<p>The COUNT function is used to count the number of rows in a database table, considering duplicates and Null.</p> Signup and view all the answers

Which function is used to summarize the data in SQL?

<p>Aggregate functions are used to summarize the data in SQL.</p> Signup and view all the answers

Which function is used to find the maximum value in a column?

<p>The MAX() function is used to find the maximum value in a column.</p> Signup and view all the answers

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Study Notes

Aggregate Functions in SQL

  • Aggregate functions perform calculations on multiple rows of a single column and return a single value.

Types of Aggregate Functions

  • SUM() is used to summarize the data in SQL.
  • MAX() is used to find the maximum value in a column.
  • COUNT() is used to count the number of rows in a database table, considering duplicates and Null.
  • AVG() is used to find the average value in a column.

COUNT() Function

  • The COUNT() function counts the number of rows in a database table, considering duplicates and Null.
  • Syntax: COUNT(*) or COUNT(expression).
  • When used with COUNT(*), it counts all rows in the table, including Null and duplicates.
  • When used with COUNT(expression), it counts the number of rows where the expression is not Null.

Scalar Functions

  • UCASE() is a scalar function that converts a string to uppercase.
  • Syntax: UCASE(string).
  • Example: UCASE('hello') returns 'HELLO'.

Key Differences

  • Aggregate functions perform calculations on multiple rows and return a single value, whereas scalar functions perform calculations on a single row and return a single value.
  • SUM() and AVG() functions differ in that SUM() returns the total value, while AVG() returns the average value.

Purpose of Aggregate Functions

  • Aggregate functions are used to summarize and analyze data in SQL.

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