Relational Query Languages| Basic sql query language

BASIC SQL QUERY LANGUAGE

INTRODUCTION-

• SQL (Structured Query Language) is a special-purpose programming language designed for managing data held in a relational database management system (RDBMS).
• SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standards (ISO) in 1987. 

WHAT CAN SQL DO?

• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database

• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
• SQL can create stored procedures in a database
• SQL can create views in a database
• SQL can set permissions on tables, procedures, and views

SQL LANGUAGES

1. Data Definition Language (DDL)

2. Data Manipulation Language (DML)

3. Data Control Language (DCL)

1) DATA DEFINITION LANGUAGE- The Data Definition Language (DDL) manages table and index structure.

COMMAND USED- CREATE, ALTER, DROP,RENAME

CREATE- creates an object (a table) in the database.

ALTER modifies the structure of an existing object in various ways, for  example, adding a column to an existing table or a constraint.

DROP deletes an object in the database, usually irretrievably, i.e., it cannot be rolled back.

RENAME rename scheme object

2) DATA MANIPULATION LANGUAGE- The Data Manipulation Language (DML) is the subset of SQL used to add, update,select and delete data.

COMMAND USED-INSERT, UPDATE, DELETE,SELECT

INSERT adds rows (formally tuples) to an existing table.

UPDATE modifies a set of existing table rows.

DELETE removes existing rows from a table.

SELECT Retrieve data from one or more table

3) DATA CONTROL LANGUAGE-The Data Control Language (DCL) authorizes users to access and manipulate data.          

COMMAND USED- GRANT, REVOKE, COMMENT

GRANT authorizes one or more users to perform an operation or a set of operations on an object.

REVOKE eliminates a grant, which may be the default grant.

COMMENT Adding the element into data dictionary

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Relational Query Languages | How to create table in sql

CREATING TABLES AND VIEWS

• CREATING TABLES

CREATE: This command is used when we want to create a new table.

syntax: create table <tname>  (col.1 data type (size) constraint <constraint name> not null , col.2 data type (size));

E.g.: create table mydoc1 (username varchar (20) constraint name_mn not null, password number(10));

• VIEWS

We can use views to display the particular values from  a table as separate sub table. for example a table emp details has 8 fields and we can build a view with 3 fields from the table.

SYNTAX- 

• For creating a view -create or replace view <view name> as  <basic query for retrieval> with read only;
• For dropping a view- Drop view view name;

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Relational Query Languages |Data Manipulation Language(DML)

DML (Data Manipulation Language)

The Data Manipulation Language (DML) is the subset of SQL used to add, update and delete data and select or retrieval.

COMMAND USED-INSERT, UPDATE, DELETE,SELECT

INSERT adds rows (formally tuples) to an existing table.

UPDATE modifies a set of existing table rows.

DELETE removes existing rows from a table.

SELECT Retrieve data from one or more table

1. INSERT COMMAND- This command is used when we want to insert a data in a new existing table.This syntax is used for inserting a single value in a each column of a table at a time.

SYNTAX: insert into <tname> (col1,col2,col3) values (‘v1’, ‘v2’ , ‘v3’);

E.G.: insert into hotel (ename , salary, place) values (‘Akash’, ‘10000’, ‘chd’);

When we want to insert a multiple values in each column of a existing table then we used a following syntax:

SYNTAX: insert into <tname> values(‘&1’, ‘&2’);

You have to enter the values  and inspite of writing this command again you can use only [(/) enter].

2.UPDATE COMMAND- This command is used when we want to update a data of existing table.

syntax: update <table name> set <condition1> where <condition2>;

E.g.: update emp set <id=525> where name=’raman’ ;

3.DELETE COMMAND-When we want to delete the data from the existing table.

syntax: delete  <table name> where <condition>;

E.g.: delete  emp where name = (‘pahul’);

4. SELECT COMMAND- Select statement is used when we want to retrieve a data from a existing table.

syntax:   select * from <table name>;

E.g. select * from emp;

When we want to retrieve a specific column from a existing table then we use a another syntax.

syntax: select <colname1> ,<colname2> from <tname>;

E.g.: select name , rollno. from emp;

When we want to retrieve a specific row from the existing table then we use following syntax:

syntax: select * from <table name> where <condition>;

E.g.: select * from emp where depno. = 10;

·    Arithmetic operation perform on a table using select command

Ø Add (+): This is used when we want to add some more content in any row of the existing table.

syntax: select <condition> from <table name>;

E.g.: select sal+1000 from emp;

Ø Between : This command is used when we want to retrieve a data in some particular range.

SYNTAX- select * from <table name> where  <condition>;

E.g.: select * from dept where deptno.. between 10 and 30;

Ø In: This command is used when we want to retrieve a particular data.

SYNTAX-  select * from <table name> where <condition>;

E.g.: select * from dept where deptno. IN(10,20,30);

Ø Null: This command is used when we want to select a null value from the existing table.

SYNTAX- select*from where <column name> is null;

E.g.: select * from where dname is null;

·   Logic condition using select command.

Ø AND

SYNTAX-select * from <table name> where <condition1> and <condition2>;

EG- select * from dept where deptno= 10 and dname= ‘sales’;

Ø OR

SYNTAX- select * from <table name> where <condition1 > or <condition2 >;

EG- select * from dept where deptno.=10 or dname = ‘sales’;

Ø NOT

SYNTAX- select*from <table name> where <condition>;

EG- select * from dept where deptno  not in (10,20,30);

·   Sorting commands for table

Ø Ascending order:

syntax: select * from <tname> order by <col name> ;

E.g: select * from dept order by depno;

Ø Descending order:

syntax: select * from <tname> order by <col name> desc;

E.g.: select * from dept order by depno dese;

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Relational Query Languages | Data Definition language(DDL)

DDL(Data Definition Language)

The Data Definition Language (DDL) manages table and index structure.
COMMAND USED- CREATE, ALTER, DROP,RENAME
CREATE creates an object (a table) in the database.
ALTER modifies the structure of an existing object in various ways, for    example, adding a column to an existing table or a constraint.
DROP deletes an object in the database, usually irretrievably, i.e., it cannot be rolled back.
RENAME rename scheme object

1. CREATE COMMAND-This command is used when we want to create a new table.

syntax: create table <tname>  (col.1 data type (size) constraint <constraint name> not null , col.2 data type (size));

E.g.: create table mydoc1 (username varchar (20) constraint name_mn not null, password number(10));

2. ALTER COMMAND- This command is used when we want to delete a particular column from a existing table.

We use three clauses with alter command:

1. ADD

2. MODIFY

3. DROP

·   ADD: This command is used when we want to create a new column.

syntax: alter table tname add (col. name data type (size));

E.g.: alter table student add (Roll no. number(100));

·   MODIFY: This command is used when we want to modify the table.

syntax: alter table tname modify (col. name data type(size));

E.g.: alter table emp modify (Branch  varchar(20));

3. DROP COMMAND- This command is used when we want to drop a table.

syntax: alter table tname drop column (col. name);

E.g.: alter table emp drop column salary; 

4.RENAME COMMAND-Rename scheme object

SYNTAX- alter table <tname> RENAME COLUMN (old column name to new column name);

E.G.- alter table emp RENAME COLUMN (name to empname);

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Relational Query Languages | Data control language (DCL)

DCL(Data Control Language)

The Data Control Language (DCL) authorizes users to access and manipulate data.        

COMMAND USED- GRANT, REVOKE, COMMENT

GRANT authorizes one or more users to perform an operation or a set of operations on an object.

REVOKE eliminates a grant, which may be the default grant.

COMMENT Adding the element into data dictionary

1.GRANT COMMAND- It authorizes one or more users to perform an operation or a set of operations on an object.

2.REVOKE COMMAND-It eliminates a grant, which may be the default grant.

EXAMPLE OF GRANT AND REVOKE COMMAND-

• Suppose that DBA(Data base administer) creates four accounts A1,A2,A3 and A4 and wants only A1 to be able to create base relations, then the DBA must issue the following GRANT command in SQL.               

          GRANT CREATE TABLE TO A1;

• Suppose that A1 creates two base relations EMPLOYEE AND DEPARTMENT.Hence A1 is then the owner of these two relations. 

EMPLOYEE RELATION  

NAME

SSN

BDATE

ADDRESS

SALARY

DNO

          

DEPARTMENT RELATION

DNUMBER

DNAME

MGR_SSN

• Next suppose that A1 wants to grant to account A2 ,the privilege to insert and delete tuples in both of these relations.However A1 does not want A2 to be able to propagate these privileges to additional accounts then A1 can issue the following command.

GRANT INSERT ,DELETE ON EMPLOYEE,DEPARTMENT TO A2;

          Here A2 has not given the Grant Option.

• Now suppose that A1 wants to allow account A3 to retrieve information from either of the two tables. A1 can issue the following command.

GRANT SELECT ON EMPLOYEE ,DEPARTMENT TO A3 WITH GRANT OPTION;

          The clause with GRANT OPTION means that A3 can now propagate the privileges to other              accounts by using GRANT.

          E.G.- A3 can grant the SELECT privilege on the EMPLOYEE relation to A4 by issuing the following command. 

GRANT SELECT ON EMPLOYEE TO A4;

• Now suppose that A1 decides to revoke the SELECT privilege on the EMPLOYEE relation from A3 .A1 then can issue this command.

REVOKE SELECT ON EMPLOYEE FROM A3;

         The DBMS must now automatically revoke the SELECT privilege on EMPLOYEE from A4 too because A3 granted that privilege to A4 and A3 does not have the privilege any more.

3. COMMENT COMMAND-Adding the element into data dictionary.A comment can appear between any keywords, parameters, or punctuation marks in a statement. You can include a comment in a statement in two ways:

• Begin the comment with a slash and an asterisk (/*). Proceed with the text of the comment. This text can span multiple lines. End the comment with an asterisk and a slash (*/). The opening and terminating characters need not be separated from the text by a space or a line break.
• Begin the comment with -- (two hyphens). Proceed with the text of the comment. This text cannot extend to a new line. End the comment with a line break.

EXAMPLE-   SELECT last_name, salary /* Select the names of the employee and their salary */

FROM EMPLOYEE /*The EMPLOYEE relation is used from where data is retrieved*/;

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