3) check constraint:
====================
=> When we want to insert the data into the table based on the certain condition, then we need to use "check constraints".
=> we can use the check constraints for more than one column within the same table.
=> check constraints allowed to define in column level as well as in table level.

Check constraints in column level:
---------------------------------
Syntax:
	create table table-name
	(
		col1 datatype,
		col2 datatype check (expression/condition),
		......
	);


Ex:
create table products11
(
    sno number(10),
    product_id int check(product_id > 0),
    product_name varchar2(50),
    product_price decimal(10,2)
);

insert into products11 values(1,101,'Laptop',59999.00);

Check Constraint at table level:
--------------------------------
Syntax:
	create table table-name
	(
		col1 datatype,
		col2 datatype,
		constraint identifier-for-constraint check(expression/condition)
	);

Note:
----
Check constraint allows the duplicated values and null values also for the corresponding columns in the table.

create table products12
(
    sno number(10),
    product_id int check(product_id > 0),
    product_name varchar2(50),
    product_price decimal(10,2),
    constraint ch_const check(product_price > 1)
);

insert into products12 values(1,1212,'Smart Tv',9999.99);

insert into products12 values(2,102102,'Mobile',19999.99);
insert into products12 values(3,112212,'Chocolates',199);
insert into products12 values(4,120120,'Speakers',9999.99);
insert into products12 values(5,null,'Refrigirator',29999.99);
insert into products12 values(6,122122,'Cooler',10000);

select * from products12;

in operator:
------------
=> which we can use to check the membership
whether the specified element/member is present in the group or not.
=> if present, in operator can return "true"
otherwise, it can return "false".
 
Ex:
'xyz' in ('abc','def','pqr') ==> false
'abc' 

create table products13
(
    sno number(10),
    product_id int check(product_id > 0),
    product_name varchar2(50) check(product_name in ('smart phone','TV','Bluetooth','Laptop')),
    product_price decimal(10,2),
    constraint ch_const1 check(product_price > 1)
);

insert into products13 values(1,112233,'TV',299);

4) Default Constraint:
======================
=> When we want to insert the table data with default values we can use "default constraints".
=> we can allow to define the default constraint at only column level.

Syntax:
	create table table-name
	(
		col1 datatype default(default-value),
		col2 datatype
	);

create table employees10
(
    employee_id int,
    employee_name varchar(50),
    designation varchar(30),
    location varchar(30),
    country varchar(20) default('India'),
    salary decimal(10,2)
);

insert into employees10(employee_id,employee_name,designation,location,salary)
values(102132,'Santosh','Fullstack Developer','Delhi',55000);

insert into employees10(employee_id,employee_name,designation,location,country,salary)
values(1012133,'Sathwik','Fullstack Developer','XYZ','USA',65000);

insert into employees10(employee_id,employee_name,designation,location,country,salary)
values(1012133,'Sathwik','Fullstack Developer','XYZ','USA',65000);

insert into employees10(employee_id,employee_name,designation,location,country,salary)
values(1012133,'Sathwik','Fullstack Developer','XYZ',null,65000);

select * from employees10;


Assignment:
-----------
1) Write a SQL query for enabling and disabling the check constraint.
Syntax:
	alter table table-name enable constraint constraint-name;
	alter table table-name disable constraint constraint-name;

2) Write a SQL query for defining the check constraint for the existing table.
Syntax:
	alter table table-name add constraint constraint-name check(expression);

3) Write a SQL query to accept the price of the product from the given range.