MySQL Interview Questions and Answers

SELECT EmpId, Project, Salary, COUNT(*) FROM EmployeeSalary GROUP BY EmpId, Project, Salary HAVING COUNT(*) > 1;

Using INTERSECT

SELECT * FROM EmployeeSalary
INTERSECT
SELECT * FROM ManagerSalary

WHERE term is used for filtering rows, and it applies to every row but HAVING term is used to filter groups.

WHERE can be used without the GROUP BY but HAVING clause cannot be used without the GROUP BY.

These are the set of rules applied to columns on the table. It is used to bound the type of data that can go into a table.

Types of constraints

• PRIMARY KEY
• FOREIGN KEY
• UNIQUE:
• Not NULL

SHOW INDEX FROM TABLE_NAME;

select count(*) from TABLE_NAME where 'status' = 1;

HEAP tables are in memory. No TEXT or BLOB fields are allowed inside HEAP tables. They are typically used for high-speed transient storage.

In MySQL, a temporary table is a distinct type of table that approves you to save a transient end result set, in which you can reuse countless instances in a single session. A brief table is created with the aid of the use of the CREATE TEMPORARY TABLE statement.

It is the best way to upload large CSV files through the LOAD DATA command.

Syntax:

LOAD DATA LOCAL INFILE "your file name" INTO TABLE table name FIELDS TERMINATED by ’,’ LINES TERMINATED BY ’\n’

The degree of a table is the number of columns in the given table. It is also called as Arity. It is the range of entities inside each entity type that can be linked via a given relationship type.