for beginners to start with SQL theory

1.  ANY USEFUL INFORMATION IS A DATA
 IN SIMPLE WORDS DATA CAN BE FACTS RELATED TO ANY OBJECT IN CONSIDERATION
 FOR EXAMPLE YOUR NAME, AGE, HEIGHT, WEIGHT, ETC. ARE SOME DATA RELATED TO YOU.
A PICTURE , IMAGE , FILE , PDF ETC. CAN ALSO BE CONSIDERED DATA
What is Data?
What is Database?
 A database is a systematic collection of data.
Databases support storage and manipulation of data.
Databases make data management easy
 Ex: An online telephone directory

2. WHAT IS A DATABASE
MANAGEMENT SYSTEM (DBMS)?
• Database Management System (DBMS) is a collection of programs which
enables its users to access database, manipulate data, reporting /
representation of data . It also helps to control access to the database.
• Database Management Systems are not a new concept and as such had been
first implemented in 1960s. Charles Bachmen's Integrated Data Store(IDS) is
said to be the first DBMS in history

3. TYPES OF DBMS:
• Hierarchical - this type of DBMS employs the "parent-child"
relationship of storing data. The windows registry used in
Windows OS is an example of a hierarchical database.
• Network DBMS - this type of DBMS supports many-to many
relations. Ex: RDM Server
• Relational DBMS - this type of DBMS defines database
relationships in form of tables, also known as relations Ex:
MySQL, Oracle and Microsoft SQL Server

4. WHAT IS RELATIONAL
DATABASE?
It is the collection of relations or two dimensional tables
Dr E.F Codd proposed the relational model for database system in 1969
Relational Model Consists of following :
• Collections of Objects or Relations
• Set of Operators to act on the relations
• Data integrity for accuracy and consistency.
(Data integrity is the one which contains correct data in the database)
To Preserve data integrity we have two types:
1.DataType: Data Type is a type of data which you store in each column
2.Constraints

5. CONSTRAINTS:
A constraint is a condition which restricts the invalid data in the table.
A constraint can be provided for a column of a table.
Types of Constraints
1. NOT NULL
2. UNIQUE
3. Primary Key
4. Foreign Key
5. Check

6. NOT NULL -
• NULL is nothing, it is neither zero nor blank space. It will not occupy any space in the memory
• NOT NULL will ensure at least some value should be present in a column
UNIQUE -
• It will not allow any duplicates in a column
• UNIQUE column can take multiple NULL (s)
Primary Key
• It is the combination of NOT NULL and UNIQUE
• Only one PK is allowed in a table
• PK identifies a record uniquely in a table

7. Foreign Key
• FK creates relationship between any two tables
• FK is created on the child table
• FK can take both NULL and duplicate values
• We can have more than 1 FK in a given table
CHECK
• It is used to provide additional validations as per the customer requirements.

8. SQL:
• Developed by IBM SQL – Structured Query Language.
• SQL – it is a language to talk to the database / to access the database
• To work on SQL , a DB software (RDBMS) is required.
• SQL is not case sensitive
What is SQL?
Structured Query language (SQL) pronounced as "S-Q-L" or sometimes as
“See-Quel” is actually the standard language for dealing with Relational
Databases. SQL can be effectively used to insert, search, update, delete
database records.

9. SQL STATEMENTS:

10. SQL STATEMENTS:
SQL SELECT Statement
SELECT column1, column2....columnN FROM table_name;
SQL WHERE Clause
SELECT column1, column2....columnN FROM table_name WHERE
CONDITION;
SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS;
SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000;

11. SQL STATEMENTS:
SQL ORDER BY Clause
SELECT column1, column2....columnN FROM table_name WHERE
CONDITION ORDER BY column_name {ASC|DESC};
SQL GROUP BY Clause
SELECT SUM(column_name) FROM table_name WHERE CONDITION
GROUP BY column_name;
SQL> SELECT * FROM CUSTOMERS ORDER BY NAME, SALARY;
SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS GROUP BY NAME;

12. SQL STATEMENTS:
SQL CREATE TABLE Statement
CREATE TABLE table_name( column1 datatype, column2
datatype, column3 datatype, ..... columnN datatype,
PRIMARY KEY( one or more columns ) );
SQL DROP TABLE Statement
DROP TABLE table_name;
SQL>
CREATE TABLE CUSTOMERS
(ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25),
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID));
SQL> DROP TABLE CUSTOMERS;
SQL> DESC CUSTOMERS;
ERROR 1146 (42S02): Table 'TEST.CUSTOMERS' doesn't exist

13. SQL STATEMENTS:
SQL TRUNCATE TABLE Statement
TRUNCATE TABLE table_name;
SQL INSERT INTO Statement
INSERT INTO table_name( column1, column2....columnN)
VALUES ( value1, value2....valueN);
SQL > TRUNCATE TABLE CUSTOMERS;
SQL> SELECT * FROM CUSTOMERS;
Empty set (0.00 sec)
INSERT INTO CUSTOMERS VALUES (7, 'Muffy', 24, 'Indore', 10000.00 );

14. SQL STATEMENTS:
SQL UPDATE Statement
UPDATE table_name SET column1 = value1, column2 =
value2....columnN=valueN [ WHERE CONDITION ];
SQL DELETE Statement
DELETE FROM table_name WHERE {CONDITION};
SQL> UPDATE CUSTOMERS SET ADDRESS = 'Pune' WHERE ID = 6;
SQL> DELETE FROM CUSTOMERS WHERE ID = 6;

15. SQL JOINS
• The SQL Joins clause is used to combine records from two or more tables in a
database. A JOIN is a means for combining fields from two tables by using values
common to each.
There are different types of joins available in SQL −
•INNER JOIN − returns rows when there is a match in both
tables.
•LEFT JOIN − returns all rows from the left table, even if there are
no matches in the right table.
•RIGHT JOIN − returns all rows from the right table, even if there
are no matches in the left table.
•FULL JOIN − returns rows when there is a match in one of the
tables.
•SELF JOIN − is used to join a table to itself as if the table were
two tables, temporarily renaming at least one table in the SQL
statement.

16. INNER JOIN:
SELECT table1.column1, table2.column2... FROM table1
INNER JOIN table2 ON table1.common_field = table2.common_field;
SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS
INNER JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

17. LEFT JOIN:
SELECT table1.column1, table2.column2... FROM table1
LEFT JOIN table2 ON table1.common_field = table2.common_field;
SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS
LEFT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

18. RIGHT JOIN:
SELECT table1.column1, table2.column2... FROM table1
RIGHT JOIN table2 ON table1.common_field = table2.common_field;
SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS
RIGHT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

19. FULL JOIN:
SELECT table1.column1, table2.column2... FROM table1
FULL JOIN table2 ON table1.common_field = table2.common_field;
SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS
FULL JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;