The document provides an overview of SQL commands and data types for creating and managing databases. It covers essential operations such as creating databases and tables, inserting data, altering table structures, querying data with the SELECT statement, and using various SQL functions and operators. Additionally, it explains how to use aggregate functions and sort query results.

1. SQL

2. Create database <dbname>;
Create database learnersnote;

3. Opening the database
• Use <databasename>;
• Use learnernote;

4. CREATE TABLE table_name (
column1 datatype [(size)]
[constraint],
column2 datatype [(size)]
[constraint],
column3 datatype [(size)]
[constraint],
The CREATE TABLE statement is used to create a new table in a database.

5. MySQL Data Types
In MySQL there are three main data types:
string, numeric, and date and time.
Numeric Data Type
1. int – used for number without decimal.
2. Decimal(m,d) /Dec(m,d) – used for floating/real numbers. m denotes the total length of
number and d is number of decimal digits.
Date and Time Data Type
1. date – used to store date in YYYY-MM-DD format.
2. time – used to store time in HH:MM:SS format.
String Data Types
1. char(m) – used to store a fixed length string. m denotes max. number of characters.
2. varchar(m) – used to store a variable length string. m denotes max. no. of characters

6. Constraint
1.NOT NULL
2.UNIQUE
3.PRIMARY KEY
4.DEFAULT
5.CHECK

7. Structure of the table
Desc <tablename>;

8. INSERTING DATA INTO TABLE –
The rows are added to relations(table) using INSERT
command of SQL.
Syntax of INSERT is :
INSERT INTO <tablename>
VALUES ( <value1> , <value2> , …..) ;
INSERT INTO <tablename>(<column1><column2>,
….)
VALUES ( <value1> , <value2> , …..) ;

9. ALTER TABLE - ADD Column
To add a column in a table, use the following
syntax:
ALTER TABLE table_name
ADD column_name datatype;

10. ALTER TABLE - DROP COLUMN
To delete a column in a table, use the following
syntax (notice that some database systems
don't allow deleting a column):
ALTER TABLE table_name
DROP column_name;

11. ALTER TABLE - MODIFY DATATYPE
To change the data type of a column in a
table, use the following syntax:
ALTER TABLE table_name
MODIFY column_name datatype;

12. ALTER TABLE table_name
CHANGE COLUMN oldcolumn_name newcolumn_name
datatype;
ALTER TABLE - RENAME COLUMN

13. DROP TABLE:
DROP TABLE command allows to remove a table
from database. Once the DROP command is
issued, the table will no longer be available in the
database.
Syntax: DROP TABLE < table name>;

14. Select Command:
It helps to display the records as per our
requirement.
SELECT column1,column2….
FROM table_name ;
Different forms of select command:
1. Select * from employee;
It displays all rows and columns from the table.

15. For displaying particular rows.
Syntax: SELECT *
FROM <tablename>
WHERE <cond>;
Eg. Select *
from employee
where gender=’M’;

16. ELIMINATING REDUNDANT DATA
The distinct keyword is used to eliminate duplicate
records from the table.
Eg.
Select distinct (gender)
from employee;

17. USING COLUMN ALIASES
The columns that we select in a query can be given a different
name, i.e.column alias name for output purpose.
Syntax:
SELECT <columnname>AS column alias ,<columnname>AS column alias
FROM<tablename>;
Eg.select ecode as “EMP_Code”
from employee;

18. CONDITION BASED ON A RANGE
The BETWEEN operator defines a range of values that the
column values must fall into make the
condition true. The range include both lower value and
upper value.
e.g.To display ECODE,ENAME and GRADE of those
employees whose salary is between 40000 and
50000,command is:
SELECT ECODE , ENAME ,GRADE FROM EMPLOYEE
WHERE GROSS BETWEEN 40000 AND 50000;

19. CONDITION BASED ON A LIST
The in operator is used to display records based on a list of
values.
Eg. To display details of employees who have scored A,B and C
grades.
Select * from employee where grade in(‘A’,’B’,’C’);
Note: For displaying records that do not match in the list, we
have to use not in operator.

20. CONDITION BASED ON PATTERN MATCHES
LIKE operator is used for pattern matching in SQL. Patterns are described
using two special
wildcard characters: % and _ (underscore)
1. percent(%)– The % character matches any substring.
2. underscore(_)– The _ character matches any single character.
e.g.To display names of employee whose name starts with R in
EMPLOYEE table, the command is:
select ename from employee where ename like “R%”;
e.g. To display details of employee whose second character in name is:
select * from employee where ename like ‘_e%’;

21. SEARCHING FOR NULL
The NULL value in a column can be searched for in a table
using IS NULL in the WHERE clause.
E.g. to list employee details whose salary contain NULL, we
use the command:
Select * from employee where gross is null;
Note: For listing employees who earn salary, then it is:
Select * from employee where gross is not null;

22. Relational Operators
• To compare two values, a relational operator is used. The result of
the comparison is true or false.
Relational Operators recognized by SQL: =, >, <, <=, >=, <> (not
equal or !=)
Eg. Select * from employee where ecode <> 1001;
Above query will not display those employee details whose ecode
column value is 1001.

23. Logical Operators- (OR, AND, NOT)
1) To list the employee details having grades E2 or E3.
Select ecode, ename, grade, gross from employee where
(grade=‘E2’ OR grade=‘E3’);
Select * from employee where department=‘it’ or sal>50;
Select * from employee where not department=‘it’;
2) To list all the employees’ details having grades as ‘E4’
but with salary < 9000.

24. Sorting Results- ORDER BY clause
Results of SQL query can be sorted in a specific order using ORDER BY clause.
The ORDER BY clause allows sorting of query results by one or more columns. The sorting can
be done either in ascending or descending order.
Eg. Select * from emp order by ename;
Above query arranges the records in alphabetical order of ename value. By default order by
clause arranges in ascending order.
TO DISPLAY RECORDS IN DESCENDING ORDER
❖ Select * from employee order by ename desc;
Above query gives output in descending order of ename.
❖ Select * from employee ORDER BY grade DESC, ename ASC;
Above query displays records first in the descending order of grade and within the same
grade,
employees are displayed in the ascending order of Ename.

25. SQL AGGREGATE FUNCTIONS:
All the aggregate functions ignore null values except count(*).
Avg – to compute average value
Min – to find minimum value
Max – to find maximum value
Sum – to find total value
Count – to count non-null values in a column
Count( *) – to count total number of rows in a table including null values.
Examples:
Select avg(gross) from employee;
Select min(gross) from employee where deptno= 10;
Select count(*) from emp where gross> 10000;
Select count (DISTINCT gender) from employee;

26. DELETE FROM table_name WHERE condition;