Question

Explain how the SELECT and WHERE commands help a user to view the necessary data from multiple database files (tables).

Answer 1

ANSWER:

As per the given question

SELECT Statement The SELECT statement is used for retrieving the required attributes or all data from one or more tables in database Syntax of SELECT Statement is as shown: SELECT column_list FROM table-name WHERE Condition SELECT keyword specifies the columns in the table FROM keyword specifies the tables from where the data is to be retrieved. WHERE clause is used to retrieve information from a table based on a condition. Here the table name is the name of the table from which a user needs the information Column list are the column in the tables

Consider the following two tables: Employee table: Employee_ID Employee_Name DeptNo 34218 Johnson 100 45079 Wilson 100 34532 Darrold 200

Department table: DeptNo DName Loc 100 Sales London 200 Accounts USA 300 Computers India Suppose the user need to know the employee id, employee name of all employees. The data can be retrieved by executing the following query:

Query: SELECT Employee_ID, Employee_Name FROM Employee Output: Employee_ID Employee_Name 34218 Johnson 45079 Wilson 34532 Darrold

Suppose the user need to know the employee id, employee name of employees who work in department 100. The data can be retrieved by executing the following query: Query: SELECT Employee_ID, Employee_Name FROM Employee WHERE deptno=100; Output: Employee_ID Employee_Name 34218 Johnson 45079 Wilson

Suppose the user need to know the employee id, employee name, department name and location of the department of employees who work in department 100. The data can be retrieved by executing the following query: Query: SELECT Employee_ID, Employee_Name, DName, Loc FROM Employee, Department WHERE DeptNo. Employee DeptNo. Department AND Deptno=100; Output: Employee_ID Employee_Name DName Loc 34218 Johnson Sales London 45079 Wilson Sales London

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