Mastering SQL Concepts

What is the purpose of an INNER JOIN in SQL?

• To retrieve matching records from two or more tables.

• To create a new table from existing tables.

• To update records in a single table.

• To delete records from two tables.

Explain the difference between LEFT JOIN and RIGHT JOIN.

• LEFT JOIN includes all rows from the left table; RIGHT JOIN includes all rows from the right table.

• LEFT JOIN excludes rows from the left table; RIGHT JOIN excludes rows from the right table.

• LEFT JOIN only returns matching rows; RIGHT JOIN returns all rows from both tables.

• LEFT JOIN and RIGHT JOIN are identical in functionality.

What SQL function would you use to count the number of rows in a table?

• TOTAL(*)

• SUM(*)

• AVG(*)

• COUNT(*)

How do you retrieve unique values from a column in SQL?

• GET UNIQUE(column_name) FROM table_name;

• SELECT ALL column_name FROM table_name;

• SELECT DISTINCT column_name FROM table_name;

• SELECT column_name FROM table_name WHERE DISTINCT;

What is the syntax for an UPDATE statement in SQL?

• UPDATE table_name WHERE condition;

• SET column1 = value1, column2 = value2 UPDATE table_name;

• UPDATE table_name SET column1 = value1;

• UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition;

Describe the role of the WHERE clause in a DELETE statement.

• The WHERE clause specifies the columns to be deleted.

• The WHERE clause is used to update records in a DELETE statement.

• The WHERE clause determines which records to delete in a DELETE statement.

• The WHERE clause determines the order of deletion in a DELETE statement.

What is a CROSS JOIN and when would you use it?

• A CROSS JOIN returns the Cartesian product of two tables.

• A CROSS JOIN is used to merge two tables into one without any duplication.

• A CROSS JOIN filters rows based on specific conditions.

• A CROSS JOIN combines rows from two tables based on a common column.

How can you combine multiple conditions in a SQL query?

• Use AND and OR operators to combine conditions.

• Combine conditions by using GROUP BY only.

• Use SELECT and FROM clauses to combine conditions.

• Conditions can only be combined in subqueries.

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

• To filter rows based on specific conditions.

• To group rows that have the same values in specified columns and perform aggregate calculations on them.

• To sort rows in ascending or descending order.

• To create new tables from existing data.

Explain the difference between aggregate functions and scalar functions in SQL.

• Aggregate functions can only be used with numeric data types; scalar functions can handle any data type.

• Scalar functions return multiple values from multiple inputs; aggregate functions return a single value from a single row.

• Aggregate functions return a single value from multiple rows; scalar functions return a single value from a single input.

• Aggregate functions operate on individual rows; scalar functions operate on entire tables.