Summary -

In this topic, we described about the below sections -

Why Select Table?

Generally, table contains the data stored as rows and columns. The table data may be a backup or a transactional or information or some other purposeful data. These data can be used in different places for different purposes. To use the data, first it should get retrieved from the table.

For example, a table contains the bank transactions information. If account holder wants to see what transactions performed in the current month for their account. That information should be retrieved from the table and gets displayed.

SELECT statement fulfils the requirement to get the data retrieved from database table.

How to use SELECT Statement?

SELECT Statement is used to fetch all the rows or specific rows data from the table. By using SELECT Statement, we can run multiple queries on one table with the help of different clauses and operators. Some of the most commonly used queries are listed as below -

Syntax -

To retrieve the specified columns from the table are -

SELECT column1, column2, …., columnN
FROM table_name 

To retrieve all the columns information –

SELECT * 
FROM table_name 
[WHERE condition];

Example –

Consider employee_details table with emp_id, emp_name, designation, manager_id, date_of_hire, salary and dept_id for understanding queries.

employee_details -

emp_id emp_name designation manager_id date_of_hire salary dept_id
001 Employee1 Director 2019-07-11 45000.00 1000
002 Employee2 Director 2019-07-11 40000.00 2000
003 Employee3 Manager Employee1 2019-07-11 27000.00 1000
004 Employee4 Manager Employee2 2019-10-08 25000.00 2000
005 Employee5 Analyst Employee3 2019-07-11 20000.00 1000
006 Employee6 Analyst Employee3 2019-10-08 18000.00 1000
007 Employee7 Clerk Employee3 2019-07-11 15000.00 1000
008 Employee8 Salesman Employee4 2019--09-09 14000.00 2000
009 Employee9 Salesman Employee4 2019-10-08 13000.00 2000

Scenario – Retrieve all columns data from the table.

Requirement – Fetch the all columns data present in the employee_details table. The query is as follows -

 SELECT * FROM employee_details; 

By executing above query, we can get whole information of the employee_details table. The output was shown as below -

emp_id emp_name designation manager_id date_of_hire salary dept_id
001 Employee1 Director 2019-07-11 45000.00 1000
002 Employee2 Director 2019-07-11 40000.00 2000
003 Employee3 Manager Employee1 2019-07-11 27000.00 1000
004 Employee4 Manager Employee2 2019-10-08 25000.00 2000
005 Employee5 Analyst Employee3 2019-07-11 20000.00 1000
006 Employee6 Analyst Employee3 2019-10-08 18000.00 1000
007 Employee7 Clerk Employee3 2019-07-11 15000.00 1000
008 Employee8 Salesman Employee4 2019--09-09 14000.00 2000
009 Employee9 Salesman Employee4 2019-10-08 13000.00 2000

Scenario – Get specified columns data from the table.

Requirement – Fetch the emp_id, emp_name columns data from the employee_details table. The query was as follows -

SELECT emp_id, emp_name FROM employee_details; 

By executing above query, we can get all rows information of emp_id, emp_name columns from employee_details table. The output was shown as below -

emp_id emp_name
001 Employee1
002 Employee2
003 Employee3
004 Employee4
005 Employee5
006 Employee6
007 Employee7
008 Employee8
009 Employee9

Scenario – Get distinct values of a column from table.

Requirement – Fetch distinct designations from employee_details table. The query was as follows -

SELECT DISTINCT designation FROM employee_details; 

By executing above query,we can get distinct designations from employee_details table. The output was shown as below -

designation
Analyst
Clerk
Director
Manager
Salesman