Most Essential And Frequently Asked Interview
Questions And Answer
Q.What is the difference between BETWEEN and IN operator in SQL?Ans.:
SQL | difference between BETWEEN and IN operator
The BETWEEN operator selects all records between the given range whereas IN operator selects all matching records given with the WHERE clause.View Detials
Q.What are the 3 different ways in PHP to connect with MySQL?Ans.:
The three different way in PHP to connect with MySQL is:
Note: We should use MySQLI because MySQLI is imporoved version of MySQL and have more function then MySQL.
Q.What is a view in SQL?Ans.:
SQL | View
View in SQL is a kind of virtual table. It does not physical exists in our database but have rows and column as there we have in a real database table. we can create a view by selecting fields from one of the tables present in the database. A View can have all the rows of a table or specific rows based on certain conditions.View Detials
Q.How can we repair a MySQL table?Ans.:
MySQL | Repair Table
REPAIR command is used for repair a MySQL table
REPAIR TABLE users
We can also specify Quick and Extended after the table name
REPAIR TABLE users QUICK
If we specify Quick then MySQL will do a repair of only the index tree.
REPAIR TABLE users EXTENDED
But if we specify the extended then it creates index row by row.
Q.Write an SQL query to find names of employee start with 'A'?Ans.:
SQL | LIKE operator
The LIKE operator of SQL is used for such kind of operations. It is used to fetch filtered data by searching for a particular pattern in where clause.View Detials
Q.How can we find the number of rows in a table using MySQL?Ans.:
MySQL | Find the number of rows in a table
We can use the below query to count the number of rows in a table
>SELECT COUNT(*) FROM table_name;
Q.What is the best collation to use for MySQL?Ans.:
MySQL | What is the best collation to use for MySQL?
Mostly we use:
utf8_general_ci is used for fast sorting but it is less accurate whereas utf8_unicode_ci is used for better accuracy but a little slow as compare to utf8_general_ci.
We can also use other collations based on specific languages like utf8_swedish_ci.
Q.How can we increase the speed of a MySQL select query?Ans.:
MySQL | Increase the speed of a MySQL select query
For increasing the speed of a query we have to do a couple of things
- First of all instead of using select * from table1, use select column1, column2, column3.. from table1.
- Try to introduce the index in the table.
- Always use the limit keyword if we are looking for any specific number of rows from the result set.
Q.What are the different storage engine present in MySQL?Ans.:
There are 5 different types of storage engine present in MySql.
- INNO DB
MyISAM is the default storage engine for MySQL
Q.What is the difference between primary key and unique constraints?Ans.:
SQL | Difference between primary key and unique constraints
There is only one primary key in a table. It creates the clustered index automatically and it cannot have NULL value
whereas there can be multiple unique constraints in a table. It does not create the clustered index automatically and it can have a NULL value
Q.How can we know the number of days between two given dates using MySQL?Ans.:
DATEDIFF function is use for finding the number of days between two given dates using MySQL
Q.Find nth largest salary from employees table?Ans.:
By using following query we can find out the nth largest salary from employees table.
SELECT salary FROM `employees` ORDER BY salary DESC LIMIT 1 OFFSET n-1
In the above query n is replaced by any number where n >= 1. Suppose you want to find fifth highest salary then you have to use offset = 5-1 i.e.: 4
The query will be:
SELECT salary FROM `employees` ORDER BY salary DESC LIMIT 1 OFFSET 4