Crake a MySql interview questions and answers of part 2

 Dear All,

11. What is the difference between the INNER JOIN and OUTER JOIN in MySQL?

INNER JOIN returns only the rows that have matching values in both tables being joined, while OUTER JOIN returns all the rows from one table and the matching rows from the other table being joined.

12. What is the use of the GROUP BY clause in MySQL?

The GROUP BY clause is used to group rows based on the values in one or more columns. It is commonly used in conjunction with aggregate functions such as COUNT, SUM, and AVG to calculate summary statistics for each group.

13. What is the use of the DISTINCT keyword in MySQL?

The DISTINCT keyword is used to return only unique values in a specified column. It is often used in conjunction with the SELECT statement to remove duplicates from the results.

14. What is the use of the INDEX keyword in MySQL?

The INDEX keyword is used to create an index on one or more columns in a table. Indexes can improve the performance of queries that involve the indexed columns, as they allow for faster lookups of specific values.

15. What is the difference between the DATE and DATETIME data types in MySQL?

The DATE data type stores only the date, while the DATETIME data type stores both the date and time. DATE is more efficient for storing only dates, while DATETIME is more flexible for storing date and time information.

16. What is the use of the MAX and MIN functions in MySQL?

The MAX function returns the maximum value in a specified column, while the MIN function returns the minimum value in a specified column. They are often used in conjunction with the GROUP BY clause to calculate summary statistics for each group.

17. What is the use of the NULL keyword in MySQL?

The NULL keyword represents a missing or unknown value in a column. It can be used in comparison operations and in the WHERE clause to filter results based on the presence or absence of a value.

18. What is the difference between a primary key and a unique key in MySQL?

A primary key is a column or set of columns that uniquely identifies each row in a table and cannot contain NULL values, while a unique key is a column or set of columns that must contain unique values but can contain NULL values.

19. What is the use of the HAVING clause in MySQL?

The HAVING clause is used to filter the results of a GROUP BY query based on aggregate functions such as COUNT, SUM, and AVG.

20. What is the difference between a left join and a right join in MySQL?

A left join returns all the rows from the left table and the matching rows from the right table, while a right join returns all the rows from the right table and the matching rows from the left table.

21. What is the use of the CONCAT function in MySQL?

The CONCAT function is used to concatenate two or more strings together. It takes any number of arguments and returns the concatenated string.

22. What is the use of the IF function in MySQL?

The IF function is used to conditionally return a value based on a specified condition. It takes three arguments: the condition to be evaluated, the value to return if the condition is true, and the value to return if the condition is false.

23. What is the use of the UNION operator in MySQL?

The UNION operator is used to combine the results of two or more SELECT statements into a single result set. The result set contains all the rows from each SELECT statement, with duplicates removed.

24. What is the use of the EXISTS keyword in MySQL?

The EXISTS keyword is used to test for the existence of rows in a subquery. It returns true if the subquery returns any rows, and false otherwise.

25. What is the use of the TRUNCATE TABLE statement in MySQL?

The TRUNCATE TABLE statement is used to delete all the rows from a table while preserving the table structure. It is faster and more efficient than the DELETE statement, as it does not generate as much transaction log activity.

26. What is the use of the RAND function in MySQL?

The RAND function is used to generate a random number between 0 and 1. It is often used in conjunction with the ORDER BY clause to randomize the order of the rows returned by a query.

27. What is the use of the SHOW command in MySQL?

The SHOW command is used to display information about various aspects of the MySQL server, such as databases, tables, columns, and users. It can be used in conjunction with other keywords such as CREATE, ALTER, and DROP to perform database operations.