Using SELECT query we can fetch data from database table. Also we can fetch data conditionally. For example, according to this course,

1. Find name and address whose mobile number is 017xxxxxxx.
2. Find the names and mobile numbers of people who are over 18 years old.
3. Find data who are live in Bangladesh.
4. Find data who are foreigner(Do not live in Bangladesh).

Using WHERE clause, we can solve all those questions.

Syntax:

SELECT * FROM table_name WHERE condition;

First see all data of contact table of account database:

SELECT * FROM contact;

Using SQL find name and address whose mobile number is 0171123377:

SELECT name, address FROM contact WHERE mobile = "0171123377";

Using SQL find the names and mobile numbers of people who are over 18 years old:

SELECT name, mobile FROM contact WHERE age > 18;

Using SQL find data who are live in BD:

SELECT * FROM contact WHERE country = "BD";

Using SQL find data who are foreigner(Do not live in BD):

SELECT * FROM contact WHERE country != "BD";

Multiple condition using WHERE clause:

1. Find data of people who are over 18 years old and do not live in Bangladesh.
2. Find data of people who are over 18 years old or live in Turkey.

Syntax:

SELECT * FROM table_name WHERE 1st_condition AND 2nd_condition AND 3rd condition ...... ; 

OR

SELECT * FROM table_name WHERE 1st_condition OR 2nd_condition OR 3rd condition ...... ; 

OR

SELECT * FROM table_name WHERE 1st_condition OR 2nd_condition AND 3rd condition ...... ; 

OR

SELECT * FROM table_name WHERE 1st_condition AND 2nd_condition OR 3rd condition ...... ; 

Using SQL find data of people who are over 18 years old and do not live in Bangladesh:

SELECT * FROM contact WHERE age > 18 AND country != "BD";

Using SQL find data of people who are over 18 years old or live in Turkey:

SELECT * FROM contact WHERE age > 18 OR country = "Turkey";