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SQL SHORT NOTES
Pratheesh Kumar N
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WHAT IS SQL
SQL is stand for structured query
language.
This database language is mainly
designed for maintaining the data in
relational database management system.
SQL is standard language for accessing
and manipulating database.
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Some of The Most Important SQL Commands
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• SELECT - extracts data from a database.
• UPDATE - updates data in a database.
• DELETE - deletes data from a database.
• INSERT INTO - inserts new data into a
database.
• CREATE DATABASE - creates a new database.
• ALTER DATABASE - modifies a database.
• CREATE TABLE - creates a new table.
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DDL COMMANDS:
DDL(data Definition Languages) used to
change the structure of the table like creating
the table ,altering the tables & deleting the
table.
All the commands in the DDL are auto
committed that means it permanently saves all
the changes in the data base .
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CREATE:
This commands is used to create a new
database and table.
Syntax:
CREATE TABLE table_name
(
column1 datatype,
column2 datatype,
column3 datatype,
…..
); 5
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ALTER:
The ALTER TABLE statement in structured
Query language allows you to add ,modify ,add
delete columns of an existing table.
Syntax:
ALTER TABLE table_name
ADD “column_name” datatype;
Example:
ALTER TABLE employee
ADD “Email” varchar(255); 6
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DROP:
The DROP TABLE statement in used
to drop an existing table in a
database. This command deletes both
the structure & records stored in table.
Syntax:
DROP TABLE table_name;
Example:
Drop TABLE Employee; 7
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TRUNCATE:
The truncate SQL statement is used to
remove all rows from a table. It is similar to
the DELETE statement with no WHERE
clause.
Syntax:
TRUNCATE TABLE table_name;
Example:
TRUNCATE TABLE Employee; 8
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DML COMMANDS:
Data manipulation language (DML)
commands in SQL deals with
manipulations of data records stored with
in the database tables.
it does not deal with changes to database
object and its structure. The commonly
knows DML commands are
INSERT,UPDATE and DELETE.
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To delete the field from a table:
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•ALTER TABLE “TABLE NAME” DROP
“FIELD NAME”;
•EXAMPLE:-
•ALTER TABLE “employee” DROP “age”;
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Delete all records from table
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• DELETE FROM “TABLE NAME”;
• EXAMPLE:-
• DELETE TABLE “employee”;
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Delete records from a table using condition
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• DELETE FROM “TABLE NAME” WHERE “CONDITION” VALUE
• CONDITION IS
• “FIELD NAME” CHECKING OPERATOR WITH VALUE
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INSERT:
SQL INSERT statement is a SQL query .it is
used to insert a single or a multiple records in a
table.
Syntax:
INSERT INTO table_name
VALUES(value1,value2,value3…);
Example:
INSERT INTO
STUDENTS(ROLL_NO,NAME,AGE,CITY)
VALUES(1,yadnyesh,19,PUNE); 14
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UPDATE:
The UPDATE s tatement is us ed to modify the exis ting
r ec or ds in a table.
Syntax:
UPDATE table_name
SET c olumn1_value1,c olumn2=value2,…
W H ER E c ondition;
Example:
U PD ATE c us tomers
SET c ontac tN ame = ‘yadu ’,c ity= ‘ p u n e ’
W H ER E C us tomer ID = 101;
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DELETE:
The DELETE
Syntax:
ALTER TABLE table_name
ADD column_name datatype;
Example:
ALTER TABLE employee
ADD Email varchar(255); 16
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DCL COMMANDS:
DCL is abstract of data control Language DCL
include commands such as GRANT , and is
concerned with rights , permission, and other
controls of the database system.
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GRANT:
It is used to give user access
privileges to a database.
Syntax:
GRANT SELECT,UPDATE ON
MY_TABLE TO SOME_USER,
ANOTHER_USER;
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REVOKE:
GRANT SELECT,UPDATE ON
MY_TABLE TO SOME_USER,
ANOTHER_USER;
Syntax:
REVOKE SELECT,UPDATE ON
MY_TABLE FROM USER1,USER2;
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TCL COMMANDS:
TCL(Transaction control language) a single
unit of work in a database is formed after the
consecutive execution of commands is known
as a transaction.
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COMMIT:
Commits a transaction The COMMIT
command saves all the transactions to the
database since the last COMMIT or
ROLLBACK command.
Syntax:
COMMIT;
Example:
DELETE FROM student WHERE AGE=20;
COMMIT; 21
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ROLLBACK:
If any error occurs with any of the SQL grouped
statements , all change need to be aborted .The
process of reversing changes is
Called rollback.
Syntax:
ROLLBACK;
Example:
DELETE FROM student WHERE AGE=20;
ROLLBACK; 22
