/*CREATE DATABASE - Creates a new database.*/
CREATE DATABASE database_name;

/*CREATE TABLE - Creates a new table in a database.*/
CREATE TABLE table_name 
(
    column1 datatype,
    column2 datatype,
    ...   
);

/*ALTER TABLE - Modifies an existing table structure*/.
ALTER TABLE table_name 
ADD column_name datatype;

/*DROP TABLE - Deletes a table from a database.*/
DROP TABLE table_name;

/*TRUNCATE TABLE - Removes all records from a table.*/
TRUNCATE TABLE table_name;

/*CREATE INDEX - Creates an index on a table.*/
CREATE INDEX index_name ON table_name (column_name);

/* DROP INDEX - Deletes an index from a table.*/
DROP INDEX index_name; ON Table_Name

/*Examples with Multiple Constraints
Example 1: Creating a Table with Various Constraints */
CREATE TABLE Employees 
(
    EmployeeID int PRIMARY KEY,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int CHECK (Age >= 18),
    Email varchar(255) UNIQUE,
    DepartmentID int,
    FOREIGN KEY (DepartmentID) REFERENCES Departments(DepartmentID)
);

/*Example 2: Adding Constraints to Existing Tables
Adding a Primary Key*/

ALTER TABLE table_name
ADD PRIMARY KEY (column_name);

/*Adding a Foreign Key*/
ALTER TABLE table_name
ADD FOREIGN KEY (column_name) REFERENCES other_table(column_name);

/*Adding a Unique Constraint*/
ALTER TABLE table_name
ADD UNIQUE (column_name);

/*Adding a Not Null Constraint*/
ALTER TABLE table_name
ALTER column column_name datatype NOT NULL;

/*Adding a Check Constraint*/
ALTER TABLE table_name
ADD CHECK (condition including column name ); E.g. (Column_Name > 0)

/*Adding a Default Constraint*/
ALTER TABLE table_name
ADD Constraint Constraint  _Name  DEFAULT 1 for  default_ColumnName;

ALTER TABLE table_name
ADD Defaut 1 For Column_Name

/*Example 2: Dropping Constraints
Dropping a Primary Key*/
ALTER TABLE table_name
DROP Constraint PRIMARY KEY_Name;

/*Dropping a Foreign Key*/
ALTER TABLE table_name
DROP Constraint  FOREIGN KEY fk_name;

/*Dropping a Unique Constraint*/
ALTER TABLE table_name
DROP Constraint  UNIQUEKEY_name;

/*Dropping a Not Null Constraint*/
ALTER TABLE table_name
Alter column column_name datatype NULL;

/*Dropping a Check Constraint*/
ALTER TABLE table_name
DROP Constraint   CHECKCONSTRAINT_name;

/*Dropping a Default Constraint*/
ALTER TABLE table_name
DROP Constraint  DEFAULTCONSTRAINT_Name;