SQL Tutorial Study Material SQL Queries Interview Questions and Answers with examples

By | February 19, 2017

SQL Tutorial Study Material SQL Queries Interview Questions and Answers with examples

SQL Tutorial SQL Study Material SQL Queries SQL Interview Questions and Answers with examples SQL Basics for Beginners and Experienced Oracle SQL Tutorial Oracle SQL Interview Questions Oracle SQL Queries with Examples

 

SQL is divided into the following

  • Data Definition Language (DDL)
  • Data Manipulation Language (DML)
  • Data Retrieval Language (DRL)
  • Transaction Control Language (TCL)
  • Data Control Language (DCL)

DDL — create, alter, drop, truncate, rename

DML — insert, update, delete

DRL — select

TCL — commit, rollback, savepoint

DCL — grant, revoke

CREATE TABLE SYNTAX

Create table <table_name> (col1 datatype1, col2 datatype2 …coln datatypen);

Ex:

     SQL> create table student (no number (2), name varchar (10), marks number (3));

INSERT




This will be used to insert the records into table.

We have two methods to insert.

  • By value method
  • By address method

 

  1. a) USING VALUE METHOD

     Syntax:

          insert into <table_name) values (value1, value2, value3 …. Valuen);

     Ex:

            SQL> insert into student values (1, ’sudha’, 100);

            SQL> insert into student values (2, ’saketh’, 200)

     To insert a new record again you have to type entire insert command, if there are lot of  

     records this will be difficult.

     This will be avoided by using address method.

 

  1. b) USING ADDRESS METHOD

      Syntax:

          insert into <table_name) values (&col1, &col2, &col3 …. &coln);

     This will prompt you for the values but for every insert you have to use forward slash.

     

      Ex:




            SQL> insert into student values (&no, ‘&name’, &marks);

 

Enter value for no: 1

Enter value for name: Jagan

Enter value for marks: 300

old   1: insert into student values(&no, ‘&name’, &marks)

new   1: insert into student values(1, ‘Jagan’, 300)

 

SQL> /

Enter value for no: 2

Enter value for name: Naren

Enter value for marks: 400

old   1: insert into student values(&no, ‘&name’, &marks)

new   1: insert into student values(2, ‘Naren’, 400)

 

  1. c) INSERTING DATA INTO SPECIFIED COLUMNS USING VALUE METHOD

    

     Syntax:

           insert into <table_name)(col1, col2, col3 … Coln) values (value1, value2, value3 ….

                                                              Valuen);

     Ex:

            SQL> insert into student (no, name) values (3, ’Ramesh’);

            SQL> insert into student (no, name) values (4, ’Madhu’);

 

  1. d) INSERTING DATA INTO SPECIFIED COLUMNS USING ADDRESS METHOD

    

     Syntax:

          insert into <table_name)(col1, col2, col3 … coln) values (&col1, &col2, &col3 …. &coln);

     This will prompt you for the values but for every insert you have to use forward slash.

     

     Ex:

            SQL> insert into student (no, name) values (&no, ‘&name’);




Enter value for no: 5

Enter value for name: Visu

old   1:  insert into student (no, name) values(&no, ‘&name’)

new   1:  insert into student (no, name) values(5, ‘Visu’)

 

SQL> /

Enter value for no: 6

Enter value for name: Rattu

old   1:  insert into student (no, name) values(&no, ‘&name’)

new   1:  insert into student (no, name) values(6, ‘Rattu’)

 

SELECTING DATA

 

Syntax:

    Select * from <table_name>;              — here * indicates all columns

or

    Select col1, col2, … coln from <table_name>;

 

Ex:

    SQL> select * from student;

   

        NO NAME            MARKS

        —  ——             ——–

         1   Sudha             100

         2   Saketh            200

         1   Jagan             300

         2   Naren             400

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 




    SQL> select no, name, marks from student;

 

        NO NAME            MARKS

        —  ——             ——–

         1   Sudha             100

         2   Saketh            200

         1   Jagan             300

         2   Naren             400

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

    SQL> select no, name from student;

 

        NO NAME

        —  ——-

         1   Sudha

         2   Saketh

         1   Jagan

         2   Naren

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

                                                     CONDITIONAL SELECTIONS AND OPERATORS

 




We have two clauses used in this

  • Where
  • Order by

 

USING WHERE

 

Syntax:

     select * from <table_name> where <condition>;

     the following are the different types of operators used in where clause.

 

  • Arithmetic operators
  • Comparison operators
  • Logical operators

 

  • Arithmetic operators — highest precedence

+, -, *, /

  • Comparison operators
    • =, !=, >, <, >=, <=, <>
  • between, not between
  • in, not in
  • null, not null
  • like
  • Logical operators
  • And
  • Or — lowest precedence
  • not




  1. a) USING =, >, <, >=, <=, !=, <>

     Ex:

        SQL> select * from student where no = 2;

        NO NAME            MARKS

        —  ——-           ———

         2   Saketh            200

         2   Naren             400

        

        SQL> select * from student where no < 2;

 

        NO NAME            MARKS

        —  ——-           ———-

         1   Sudha             100

         1   Jagan             300

 




        SQL> select * from student where no > 2;

 

         NO NAME            MARKS

         —  ——-           ———-

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

         SQL> select * from student where no <= 2;

 

         NO NAME            MARKS

         —  ——-           ———-

         1   Sudha             100

         2   Saketh            200

         1   Jagan             300

         2   Naren             400

      

         SQL> select * from student where no >= 2;

 

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         2   Naren             400

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

         SQL> select * from student where no != 2;

 




         NO NAME            MARKS

         —  ——-           ———-

         1   Sudha             100

         1   Jagan             300

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

         SQL> select * from student where no <> 2;

 

         NO NAME            MARKS

         —  ——-           ———-

         1   Sudha             100

         1   Jagan             300

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

  1. b) USING AND

    

     This will gives the output when all the conditions become true.

    

     Syntax:

          select * from <table_name> where <condition1> and <condition2> and .. <conditionn>;

    

     Ex:

 

         SQL> select * from student where no = 2 and marks >= 200;

 

 

                              NO NAME            MARKS

         —  ——-           ——–

         2   Saketh            200

         2   Naren             400

 

  1. c) USING OR

 

     This will gives the output when either of the conditions become true.

 




     Syntax:

         select * from <table_name> where <condition1> and <condition2> or .. <conditionn>;

 

     Ex:

         SQL> select * from student where no = 2 or marks >= 200;

 

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         1   Jagan             300

         2   Naren             400

 

  1. d) USING BETWEEN

 

     This will gives the output based on the column and its lower bound, upperbound.

 

     Syntax:

         select * from <table_name> where <col> between <lower bound> and <upper bound>;

 

     Ex:

         SQL> select * from student where marks between 200 and 400;

 

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         1   Jagan              300

         2   Naren              400

 



  1. e) USING NOT BETWEEN

 

     This will gives the output based on the column which values are not in its lower bound,

     upperbound.

 

     Syntax:

     select * from <table_name> where <col> not between <lower bound> and <upper bound>;

 

     Ex:

         SQL> select * from student where marks not between 200 and 400;

 

         NO NAME            MARKS

         —  ——-           ———

         1   Sudha             100

 

  1. f) USING IN

 

    This will gives the output based on the column and its list of values specified.

 




    Syntax:

         select * from <table_name> where <col> in ( value1, value2, value3 … valuen);

 

     Ex:

         SQL> select * from student where no in (1, 2, 3);

 

         NO NAME            MARKS

         — ——-            ———

         1   Sudha             100

         2   Saketh            200

         1   Jagan             300

         2   Naren             400

         3   Ramesh

 

  1. g) USING NOT IN

 

     This will gives the output  based on the column which values are not in the list of values  

     specified.

 

     Syntax:

         select * from <table_name> where <col> not in ( value1, value2, value3 … valuen);

 

     Ex:

         SQL> select * from student where no not in (1, 2, 3);

 

         NO NAME            MARKS

         —  ——-           ———

         4   Madhu

         5   Visu

         6   Rattu

 

  1. h) USING NULL

 

     This will gives the output based on the null values in the specified column.

 

     Syntax:

         select * from <table_name> where <col> is null;

 

     Ex:

         SQL> select * from student where marks is null;




 

         NO NAME            MARKS

         —  ——-           ———

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 

  1. i) USING NOT NULL

 

    This will gives the output based on the not null values in the specified column.

 

     Syntax:

         select * from <table_name> where <col> is not null;

 

     Ex:         

         SQL> select * from student where marks is not null;

         NO NAME            MARKS

         —  ——-           ———

         1   Sudha             100

         2   Saketh            200

         1   Jagan             300

         2   Naren             400




 

  1. j) USING LIKE

 

    This will be used to search through the rows of database column based on the pattern you

     specify.

 

     Syntax:

        select * from <table_name> where <col> like <pattern>;

    

     Ex:         

  1. i) This will give the rows whose marks are 100.

 

            SQL> select * from student where marks like 100;

 

         NO NAME            MARKS

         —  ——-           ———

         1   Sudha             100

       

  1. ii) This will give the rows whose name start with ‘S’.

 

             SQL> select * from student where name like ‘S%’;

 

         NO NAME            MARKS

         —  ——-           ———

         1   Sudha             100

         2   Saketh            200

 




        iii) This will give the rows whose name ends with ‘h’.

 

              SQL> select * from student where name like ‘%h’;

         

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         3   Ramesh

 

        iV) This will give the rows whose name’s second letter start with ‘a’.

 

               SQL> select * from student where name like ‘_a%’;

 

          NO NAME            MARKS

          —  ——-            ——–

          2   Saketh            200

          1   Jagan             300

          2   Naren             400

          3   Ramesh

          4   Madhu

          6   Rattu




 

  1. V) This will give the rows whose name’s third letter start with ‘d’.

 

              SQL> select * from student where name like ‘__d%’;

 

         NO NAME            MARKS

         —  ——-           ———

         1   Sudha             100

         4   Madhu

 

        Vi) This will give the rows whose name’s second letter start with ‘t’ from ending.

 

               SQL> select * from student where name like ‘%_t%’;

 

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         6   Rattu

        




        Vii) This will give the rows whose name’s third letter start with ‘e’ from ending.

 

                SQL> select * from student where name like ‘%e__%’;

 

         NO NAME            MARKS

         —  ——-           ———

         2   Saketh            200

         3   Ramesh

 

        Viii) This will give the rows whose name  cotains 2 a’s.

 

                    SQL> select * from student where name like ‘%a% a %’;

 

         NO NAME            MARKS

          — ——-           ———-

         1   Jagan             300

 




* You have to specify the patterns in like using underscore ( _ ).

USING ORDER BY

 

This will be used to ordering the columns data (ascending or descending).

 

Syntax:

        Select * from <table_name> order by <col> desc;

By default oracle will use ascending order.

If you want output in descending order you have to use desc keyword after the column.

 

Ex:

        SQL> select * from student order by no;

 

        NO NAME            MARKS

        —  ——-           ———

         1   Sudha             100

         1   Jagan              300

         2   Saketh            200

         2   Naren             400

         3   Ramesh

         4   Madhu

         5   Visu

         6   Rattu

 




        SQL> select * from student order by no desc;

 

        NO NAME            MARKS

        —  ——-           ———

         6 Rattu

         5 Visu

         4 Madhu

         3 Ramesh

         2 Saketh            200

         2 Naren             400

         1 Sudha             100

         1 Jagan             300

USING DML

 

USING UPDATE

 

This can be used to modify the table data.




 

Syntax:

     Update <table_name> set <col1> = value1, <col2> = value2 where <condition>;

 

Ex:

     SQL> update student set marks = 500;

     If you are not specifying any condition this will update entire table.

 

     SQL> update student set marks = 500 where no = 2;

     SQL> update student set marks = 500, name = ‘Venu’ where no = 1;

 

USING DELETE

 

This can be used to delete the table data temporarily.

 

Syntax:

    Delete <table_name> where <condition>;

 




Ex:

     SQL> delete student;

     If you are not specifying any condition this will delete entire table.

 

     SQL> delete student where no = 2;


USING DDL

 

USING ALTER

 

This can be used to add or remove columns and to modify the precision of the datatype.

 

  1. a) ADDING COLUMN

 

    Syntax:




        alter table <table_name> add <col datatype>;

 

    Ex:

        SQL> alter table student add sdob date;

 

  1. b) REMOVING COLUMN

 

    Syntax:

        alter table <table_name> drop <col datatype>;

 

    Ex:

         SQL> alter table student drop column sdob;

 

  1. c) INCREASING OR DECREASING PRECISION OF A COLUMN

 

    Syntax:

          alter table <table_name> modify <col datatype>;

    Ex:

          SQL> alter table student modify marks number(5);

 




          * To decrease precision the column should be empty.

 

  1. d) MAKING COLUMN UNUSED

 

    Syntax:

         alter table <table_name> set unused column <col>;

    Ex:

         SQL> alter table student set unused column marks;

   

         Even though the column is unused still it will occupy memory.

 

  1. d) DROPPING UNUSED COLUMNS

 

    Syntax:

        alter table <table_name> drop unused columns;

 

    Ex:

        SQL> alter table student drop unused columns; 

        * You can not drop individual unused columns of a table.




 

  1. e) RENAMING COLUMN

 

    Syntax:

        alter table <table_name> rename column <old_col_name> to <new_col_name>;

 

    Ex:

        SQL> alter table student rename column marks to smarks; 

 

USING TRUNCATE

 

This can be used to delete the entire table data permanently.

Syntax:

      truncate table <table_name>;

 

Ex:

     SQL> truncate table student;




 

USING DROP

 

This will be used to drop the database object;

 

Syntax:

     Drop table <table_name>;

 

Ex:

     SQL> drop table student;

 

USING RENAME

 

This will be used to rename the database object;

 

Syntax:

     rename <old_table_name> to <new_table_name>;

 

Ex:

     SQL> rename student to stud;

 

USING TCL

 

USING COMMIT

 




This will be used to save the work.

Commit is of two types.

  • Implicit
  • Explicit

 

  1. a) IMPLICIT

 

     This will be issued by oracle internally in two situations.

  • When any DDL operation is performed.
  • When you are exiting from SQL * PLUS.

 

  1. b) EXPLICIT

 

     This will be issued by the user.

 

     Syntax:

                Commit or commit work;

              * When ever you committed then the transaction was completed.

 




USING ROLLBACK

 

This will undo the operation.

This will be applied in two methods.

  • Upto previous commit
  • Upto previous rollback

 

Syntax:

Roll or roll work;

Or

Rollback or rollback work;

* While process is going on, if suddenly power goes then oracle will rollback the transaction.

USING SAVEPOINT

 

You can use savepoints to rollback portions of your current set of transactions.

 

Syntax:

     Savepoint <savepoint_name>;

 

Ex:

     SQL> savepoint s1;

     SQL> insert into student values(1, ‘a’, 100);

     SQL> savepoint s2;

     SQL> insert into student values(2, ‘b’, 200);

     SQL> savepoint s3;

      SQL> insert into student values(3, ‘c’, 300);

     SQL> savepoint s4;

      SQL> insert into student values(4, ‘d’, 400);




    

     Before rollback

 

     SQL> select * from student;

 

        NO NAME      MARKS

        —  ——-     ———-

         1          a         100

         2          b         200

         3          c         300

         4          d         400

     SQL> rollback to savepoint s3;

                                    Or

     SQL> rollback to s3;

    

    This will rollback last two records.

     SQL> select * from student;

 




        NO NAME      MARKS

        —  ——-     ———-

         1          a         100

         2          b         200

 

USING DCL

 

DCL commands are used to granting and revoking the permissions.

 

USING GRANT

 

This is used to grant the privileges to other users.

 

Syntax:

     Grant <privileges> on <object_name> to <user_name> [with grant option];

 

Ex:

     SQL> grant select on student to sudha;         — you can give individual privilege

      SQL> grant select, insert on student to sudha;       — you can give set of privileges

     SQL> grant all on student to sudha;                — you can give all privileges




    

     The sudha user has to use dot method to access the object.

     SQL> select * from saketh.student;

     The sudha user can not grant permission on student table to other users. To get this type of

     option use the following.

     SQL> grant all on student to sudha with grant option;             

     Now sudha user also grant permissions on student table.

 

USING REVOKE

 

This is used to revoke the privileges from the users to which you granted the privileges.

 

Syntax:

     Revoke <privileges> on <object_name> from <user_name>;

 




Ex:

     SQL> revoke select on student form sudha; — you can revoke individual privilege

     SQL> revoke select, insert on student from sudha;            — you can revoke set of privileges

      SQL> revoke all on student from sudha;       — you can revoke all privileges

      

 

USING ALIASES

 

CREATE WITH SELECT

 

We can create a table using existing table [along with data].

 

Syntax:

    Create table <new_table_name> [col1, col2, col3 … coln] as select * from




                                                               <old_table_name>;

 

Ex:

    SQL> create table student1 as select * from student;

   

    Creating table with your own column names.

    SQL> create table student2(sno, sname, smarks) as select * from student;

   

    Creating table with specified columns.

    SQL> create table student3 as select no,name from student;

 

    Creating table with out table data.

    SQL> create table student2(sno, sname, smarks) as select * from student where 1 = 2;

    In the above where clause give any condition which does not satisfy.

   




INSERT WITH SELECT

 

Using this we can insert existing table data to a another table in a single trip. But the table structure should be same.

 

Syntax:

     Insert into <table1> select * from <table2>;   

 

Ex:

     SQL> insert into student1 select * from student;

 

     Inserting data into specified columns

     SQL> insert into student1(no, name) select no, name from student;

COLUMN ALIASES

 




Syntax:

     Select <orginal_col> <alias_name> from <table_name>;

 

Ex:

     SQL> select no sno from student;

or

     SQL> select no “sno” from student;

 

TABLE ALIASES

 

If you are using table aliases you can use dot method to the columns.

 

Syntax:

     Select <alias_name>.<col1>, <alias_name>.<col2> … <alias_name>.<coln> from

                                                       <table_name> <alias_name>;

 

Ex:

     SQL> select s.no, s.name from student s;




USING MERGE

 

MERGE

You can use merge command to perform insert and update in a single command.

 

Ex:

 

SQL> Merge into student1 s1

        Using (select *From student2) s2

        On(s1.no=s2.no)

        When matched then

        Update set marks = s2.marks

        When not matched then

        Insert (s1.no,s1.name,s1.marks)

        Values(s2.no,s2.name,s2.marks);

 




In the above the two tables are with the same structure but we can merge different structured    

tables also but the datatype of the columns should match.

 

Assume that student1 has columns like no,name,marks and student2 has columns like no,       

name, hno, city.

 

SQL> Merge into student1 s1

        Using (select *From student2) s2

        On(s1.no=s2.no)

        When matched then

        Update set marks = s2.hno

        When not matched then

        Insert (s1.no,s1.name,s1.marks)

        Values(s2.no,s2.name,s2.hno);

 




MULTIPLE INSERTS

 

We have table called DEPT with the following columns and data

 

DEPTNO         DNAME           LOC

——–            ——–            —-

10                    accounting    new york

20                    research        dallas

30                    sales               Chicago

40                    operations    boston

 

  1. a) CREATE STUDENT TABLE

 

     SQL> Create table student(no number(2),name varchar(2),marks number(3));

 

  1. b) MULTI INSERT WITH ALL FIELDS

 




     SQL> Insert all

             Into student values(1,’a’,100)

             Into student values(2,’b’,200)

             Into student values(3,’c’,300)

             Select *from dept where deptno=10;

 

     — This inserts 3 rows

 

  1. c) MULTI INSERT WITH SPECIFIED FIELDS

 

     SQL> insert all

             Into student (no,name) values(4,’d’)

             Into student(name,marks) values(’e’,400)

             Into student values(3,’c’,300)

             Select *from dept where deptno=10;

 

     — This inserts 3 rows

 

  1. d) MULTI INSERT WITH DUPLICATE ROWS

 

     SQL> insert all

             Into student values(1,’a’,100)

             Into student values(2,’b’,200)

             Into student values(3,’c’,300)

             Select *from dept where deptno > 10;

 

     — This inserts 9 rows because in the select statement retrieves 3 records (3 inserts for each   

        row retrieved)




 

  1. e) MULTI INSERT WITH CONDITIONS BASED

 

     SQL> Insert all

             When deptno > 10 then

             Into student1 values(1,’a’,100)

             When dname = ‘SALES’ then

             Into student2 values(2,’b’,200)

             When loc = ‘NEW YORK’ then

             Into student3 values(3,’c’,300)

             Select *from dept where deptno>10;

 

     — This  inserts 4 rows because the first condition satisfied 3 times, second condition 

         satisfied once and the last none.

 

  1. f) MULTI INSERT WITH CONDITIONS BASED AND ELSE

 

    SQL> Insert all

            When deptno > 100 then

            Into student1 values(1,’a’,100)

            When dname = ‘S’ then

            Into student2 values(2,’b’,200)

            When loc = ‘NEW YORK’ then

            Into student3 values(3,’c’,300)

            Else

            Into student values(4,’d’,400)

            Select *from dept where deptno>10;

 




     — This inserts 3 records because the else satisfied 3 times

 

  1. g) MULTI INSERT WITH CONDITIONS BASED AND FIRST

 

     SQL> Insert first

             When deptno = 20 then

             Into student1 values(1,’a’,100)

             When dname = ‘RESEARCH’ then

             Into student2 values(2,’b’,200)

             When loc = ‘NEW YORK’ then

             Into student3 values(3,’c’,300)

             Select *from dept where deptno=20

     — This inserts 1 record because the first clause avoid to check the remaining conditions   

         once the condition is satisfied.

  1. h) MULTI INSERT WITH CONDITIONS BASED, FIRST AND ELSE





     SQL> Insert first

             When deptno = 30 then

              Into student1 values(1,’a’,100)

              When dname = ‘R’ then

              Into student2 values(2,’b’,200)

              When loc = ‘NEW YORK’ then

              Into student3 values(3,’c’,300)

              Else

              Into student values(4,’d’,400)

              Select *from dept where deptno=20

     — This inserts 1 record because the else clause satisfied once

  1. i) MULTI INSERT WITH MULTIBLE TABLES

    SQL> Insert all

            Into student1 values(1,’a’,100)

            Into student2 values(2,’b’,200)

            Into student3 values(3,’c’,300)

            Select *from dept where deptno=10;




    — This inserts 3 rows

    ** You can use multi tables with specified fields, with duplicate rows, with conditions, with 

          first and else clauses.

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Oracle SQL Tutorial Study Material SQL Queries Interview Questions and Answers with examples




SQL Tutorial Study Material SQL Queries Interview Questions and Answers with examples

 

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