SQL Tools(Create DB, Create Table, UNION, UNION ALL, NOT NULL, UNIQUE, PRIMARY KEY, Foreign Key)

To Create Database :-
CREATE DATABASE Db_Name

To Create Table :-

CREATE TABLE Person
(
@ID INT NOT NULL,
@Name VARCHAR(20),
@ADDRESS VARCHAR(255) NOT NULL,
@PS_NO SMALLINT,
@FIRST_CHAR CHAR
)

if a column contains NOT NULL values then it means it does not allow the null values.

Unique :-

CREATE TABLE Person
(
@ID INT NOT NULL UNIQUE,
@Name VARCHAR(20),
@ADDRESS VARCHAR(255) NOT NULL,
@PS_NO SMALLINT,
@FIRST_CHAR CHAR
)

Another way to represent is and the way to define primary key :-

CREATE TABLE Person
(
@ID INT NOT NULL,
@Name VARCHAR(20),
@ADDRESS VARCHAR(255) NOT NULL,
@PS_NO SMALLINT,
@FIRST_CHAR CHAR,
UNIQUE(@ID),
PRIMARY KEY(@ID)
)

A primary key value can not have null values.

If more than one column has unique value then below way we will handle :-
UNIQUE(@ID, @ADDRESS)

FOREIGN KEY :-

If a table does not have primary key then it points to a primary key to another table then that key calls a foreign key for that table like :-

CREATE TABLE Person_Values
(
@P_ID INT NOT NULL,
@ID INT NOT NULL,
@P_Name VARCHAR(20),
@P_ADDRESS VARCHAR(255) NOT NULL,
@P_PS_NO SMALLINT,
@P_FIRST_CHAR CHAR,
FOREIGN KEY (@Id) REFERENCES Persons(@Id)
)

@ID is a primary key of Persons table and now working as a foreign key for Person_Values table.

UNION AND UNION ALL :-
Union will select the distinct values from both columns. In more general form Union with distinct values
Union All select all the values from selected columns.

UNION :-

SELECT column_name From table1
UNION
SELECT column_name From table2

UNION ALL :-

SELECT column_name From table1
UNION ALL
SELECT column_name From table2