oracle basic queries

Data Types

By: Prakhar Jha

CHAR(size)

- used to store fixed length string.

-max size 255 character.

VARCHAR2(size)

-used to store variable length string .

-it can store letter, number and punctuation marks.

-max size 4000 character.

• VARCHAR(size)

-same as CHAR(size),but speed is less.

-it is also used for storing string of variable length.

• NUMBER(precision , scale)

-’precision’ total no of digits that can be stored.

-’scale’ total no of digits after decimal.

e.g. : NUMBER(4) or NUMBER(4,2) or NUMBER.

Actual

Data

Defined

As

Stored As

123456.78

9

NUMBER(

6,2)

1234.79

123456.78

9

NUMBER(

6)

123457

123456.78

9

NUMBER(

6,-2)

123500

123456.78

9

NUMBER 123456.78

9

DATE

LONG

-used to store variable length

text, of very large size

-max size 2GB.

Binary Types

• RAW(size)

-used to store binary digit of max

size 255 bytes.

• LONG RAW

-in this data type, it is possible to

store binary data upto 2GB

Object Type

• BLOB

(Binary Large Object)

-this is used for storing binary data of very large size.

-data stored like images and videos.

-max size 4GB

• CLOB

(Character Large Object)

-this data type is used to store very large character object.

-data stored like text document.

-max size 4GB.

*In one table, more than one “lob” type data type can be stored.

Commands

CREATE AND INSERT

(basic) CREATE TABLE <table_name>(<column_name>

<data_type>, <column_name> <data_type>,

<column_name> <data_type>);

DESC <table_name>;

INSERT INTO <table_name> VALUES (‘<value>’, ’<value>’ ,

’<value>’);

INSERT INTO <table_name> VALUES (‘&<value>’,

‘&<value>’, ‘&<value>’);

SELECT and UPDATE and

DELETE SELECT * FROM <table_name>;

SELECT <column_name>,<column_name> FROM <table_name>;

SELECT * FROM <table_name> WHERE <column_name> = ‘<value>’;

UPDATE <table_name> SET <column_name> = ‘<value>’;

UPDATE <table_name> SET <column_name>=‘<value>’ WHERE <condition>;

DELETE FROM <table_name>;

DELETE FROM <table_name> WHERE <condition>;

ALTER and DROP

ALTER TABLE <table_name> ADD (<column_name>

<data_type>(size));

ALTER TABLE <table_name> DROP COLUMN

<column_name>;

ALTER TABLE <table_name> MODIFY(<column_name>

<data_type>(size));

DROP TABLE <table_name>;

DISTINCT and ORDER BY

SELECT DISTINCT <column_name> FROM <table_name>;

SELECT DISTINCT * FROM <table_name>;

SELECT * FROM <table_name> ORDER BY

<column_name>;

SELECT * FROM <table_name> ORDER BY

<column_name> DESC;

CREATE and INSERT using

previous table. CREATE TABLE <table_name a> (<column_name a>, <column_name

a>,…) AS SELECT <column_name b>, <column_name b>,… FROM <table_name b>;

CREATE TABLE <table_name a> (<column_name a>, <column_namea>,…) AS SELECT <column_name b>, <column_name b>,… FROM <table_name b> WHERE <any_false_condition>;

The above query will create a new table same as <table_name b> but with no records. This is because the condition can never be fulfilled.

INSERT INTO <table_name b> SELECT <column_name>, <column_name>,… FROM <table_name a>;

INSERT INTO <table_name b> SELECT <column_name a>, <column_name a>,… FROM <table_name a> WHERE <condition>;

RENAME & VIEW TABLES

RENAME <table_name a> TO <table_nameb>;

SELECT * FROM TAB;

Data Constraints

PRIMARY KEY and

COMPOSITE KEYTo identify each row uniquely in a table in RDBMS, the concept of primary key is developed.

If it is not possible to identify data uniquely based on single column, PRIMARY KEY is

applied on multiple column and that thing is known as COMPOSITE KEY.

It is applied on a particular column.

• CREATE TABLE <table_name> (<column_1> <data_type>(size) PRIMARY KEY,

<column_2> <data_type>(size), <column_3> <data_type> (size));

Column 1 has PRIMARY KEY CONSTRAINT.

• CREATE TABLE <table_name> (<col_1> <data_type>(size), <col_2>

<data_type>(size), <col_3> <data_type>(size) , PRIMARY KEY (col_1,col_2,col_3));

col_1,col_2,col_3 together have PRIMARY KEY CONSTRAINT on them.

AUTO INCREMENT

-to set auto increment in oracle. We have to create SEQUENCE

• CREATE SEQUENCE <name>

MINVALUE 1

START WITH 1

INCREMENT BY 1

CACHE 10;

-now when we insert a value to a primary key column, we will use this sequence object to insert our new values.

• INSERT INTO <table_name> (<column_name>, <column_name>, <column_name>) values(<name>.nextval, <value>, <value>);

-<name>.nextval will return the next number in SEQUENCE.

FOREIGN KEY

<table_name a> - Detail Table or Foreign Table.

-when a table is created and FK is described in it, that table is known as Detail Table to the table where this FK is PK to that table.

<table_name b> - Master Table or Primary Table.

-the actual table whose PK is being described in other table as FK.

• CREATE TABLE <table_name a> (

<col_1> <data_type>(size) PRIMARY KEY,

<col_2> <data_type>(size) REFERENCES <table_name b> [(<column_name>)],

<col_3> <data_type>(size) ) ;

-oracle automatically associates <table_name b>’s PK to <col_2> and described <col_2> as FK, if we don’t mention <column_name> after “REFERENCE <table_name>” .

CREATE TABLE <table_name a>(

<col_1> <data_type>(size) PRIMARY KEY,

<col_2> <data_type>(size)

CONSTRAINT <constraint_name> FOREIGN KEY(col_2)

REFERENCES <table_name b>(<column_name>)

);

[CONSTRAINT [symbol]] FOREIGN KEY [index_name]

(index_col_name, ...) REFERENCES tbl_name

(index_col_name,...) [ON DELETE reference_option] [ON UPDATE

reference_option]

-reference_option: RESTRICT | CASCADE | SET NULL | NO

ACTION

CREATE TABLE <table_name a> (<col_1> <data_type>(size) PRIMARY KEY, <col_2> <data_type>(size), <col_3> <data_type>(size), FOREIGN KEY(col_2) REFERENCES <table_name b>(<column_name>) );

CREATE TABLE <table_name a> (<col_1> <data_type>(size) PRIMARY KEY, <col_2> <data_type>(size), <col_3> <data_type>(size), FOREIGN KEY(col_2) REFERENCES <table_name b>(<column_name>) ) ON DELETE CASCADE;

- “ON DELETE CASCADE” will delete the associated record from <table_namea> if any record is deleted in the Master Table or <table_name b>.

CREATE TABLE <table_name a> (<col_1> <data_type>(size) PRIMARY KEY, <col_2> <data_type>(size), <col_3> <data_type>(size), FOREIGN KEY(col_2) REFERENCES <table_name b>(<column_name>) ) ON DELETE SET NULL;

- “ON DELETE SET NULL” will set NULL in <table_name a> at the places where the record is associated to the Master Table or <table_name b>, if the record is deleted from master table.

UNIQUE KEY

- UK constraint is similar to PK.

-if we apply UK constraint on any column that column can store NULL values in them, this thing is not possible with PK contraint.

-a column with UK constraint on it can have multiple NULL value, but when there is actual value stored, no two values can be similar.

• CREATE TABLE <table_name> (

<col 1> <data_type> UNIQUE ,

<col 2> <data_type>,

<col 3> <data_type> );

• CREATE TABLE <table_name> (

<col 1> <data_type> ,

<col 2> <data_type>,

<col 3> <data_type> ,

UNIQUE(col 1));

Business Rule Constraint i.e.

CHECK Constraint CREATE TABLE <table_name> (

<col 1> <data_type>(size),

<col 2> <data_type>(size),

<col 3> <data_type>(size) CHECK(<col 3> == 2000),

CHECK(<col 1> LIKE ‘E%’)

);

-in the above query the CHECK constraint is applied on <col 1> & <col3>

- in <col 1>, it will check if the value which is being inserted, starts from ‘E’ or not.

- in <col 3>, it will check if the value which is being inserted, equals to ‘2000’ or not.

Syntax :

CHECK(<logical_expression>)

Defining Integrity Constraints by

ALTER command ALTER TABLE <table_name a> ADD FOREIGN

KEY(<col_name>) REFERENCES <table_name

b>(<col_name>);

ALTER TABLE <table_name> ADD PRIMARY

KEY(<col_name>);

ALTER TABLE <table_name> DROP PRIMARY KEY;

NOT NULL and DEFAULT

CREATE TABLE <table_name>(

<col 1> <data_type>(size) PRIMARY KEY,

<col 2> <data_type>(size) NOT NULL

);

-the insert query wont execute, if there is no data for <col 2>.

CREATE TABLE <table_name>(

<col 1> <data_type>(size) PRIMARY KEY,

<col 2> <data_type>(size) DEFAULT <value>

);

-if value is string, wrap it in single quotes.

-if number no need to wrap it.

USER_CONTRAINTS table

DESC USER_CONSTRAINTS;

SELECT <column_name> FROM

USER_CONSTRAINTS WHERE

TABLE_NAME =‘<table_name>’ ;

Data Manipulation In SQL

Operators

Arithmetic Comparison

‘+’ : Addition

‘-’ : Subtraction

‘*’ : Multiplication

‘/’ : Division

‘<’ : Is less than

‘>’ : Is greater than

‘<=’ : Is less than or equal to

‘>=’ : Is greater than or equal to

‘=’ : Is equal to

‘!=’ : is NOT equal to

Logical Operators

AND : Logical AND Operator.

OR : Logical OR Operator.

NOT : Logical NOT Operator.

examples:

AND

SELECT * FROM EMPLOYEES WHERE

SALARY > 10000 AND SALARY < 25000;

OR

SELECT * FROM SUBJECTS WHERE

NAME = ‘java’ AND NAME < ‘oracle’ ;

NOT

SELECT * FROM EMPLOYEE WHERE

NOT(SALARY > 25000)

Using AND and OR together

SELECT * FROM EMPLOYEE

WHERE

salary > 25000 AND ( designation= ‘mngr’ OR designation=

‘sec’ );

Range Searching

SELECT * FROM <table_name>

WHERE <col_name> BETWEEN ‘<value 1>’ AND ‘<value

2>’ ;

- in the output, the tuple(row) with <value 1> and <value 2> will

be included.

Pattern Matching

LIKE Predicate IN and NOT IN Predicate


WHERE <col_name> LIKE

‘E%’;


WHERE <col_name> LIKE

‘%E’;

Assume <col_name> = ‘name’

- when the above query is executed the output will show all the records whose ‘name’ are starting with the letter ‘E’ or ending with letter ‘E’ in the second query.

SELECT * FROM <table_name> WHERE <col_name> IN (‘<value>’);

- the braces after IN can hold multiple value each of which is separated by comma.

- the output will contain all records(rows) where the values of <col_name> matches to <value>.


WHERE <col_name> NOT IN (‘<value>’);

-the exact opposite of above query will happen in this query.

Renaming Columns and Tables

Column Alias Table Alias

SELECT last_name AS FAMILY,

first_name FROM persons;

-output

FAMILY FIRST_NAME

Jha prakhar

Soni rohit

Yadav ankit

Patel sachin

SELECT * FROM

<table_name> “<table

_alias>” ;

DUAL Table in Oracle

-we use SELECT command to retrieve output from a table, and it is compulsory to write a table name with it. But some time when we need to perform any Arithmetic Calculation or use some Function, at that point of time we cannot use any table name because it will return unexpected results, and using SELECT without table name is incomplete.

For this purpose we use DUAL table.

DESC DUAL;

SELECT * FROM DUAL;

SELECT 2+2 FROM DUAL; output : 4

SELECT 2*3 FROM DUAL; output: 6

SYSDATE:

SELECT SYSDATE FROM DUAL; output: current date of your system

Oracle Functions

Group Function and Scalar

Functions

-function that works on a set of values are known as Group Functions or Aggregate Functions, when we apply any function on a table's column, it generate output according to all the values that is selected by the executed query.

-function that works on single value are known as scalar functions, they are also known as ‘single row function’ .

Group Functions

SELECT AVG(marks) AS “Average Marks” FROM STUDENTS ;

SELECT COUNT(*) AS “No Of Rows” FROM STUDENTS ;

SELECT COUNT(name) AS “No Of Rows” FROM STUDENTS ;

SELECT MAX(marks) AS “Maximum Marks” FROM STUDENTS;

SELECT MIN(marks) AS “Minimum Marks” FROM STUDENTS;

SELECT SUM(marks) AS “Sum Of Marks” FROM STUDENTS:

- in above example ‘marks’ & ‘name’ are column in table ‘STUDENTS’ .

- ‘ * ’ used above can be replaced by column names as well.

Scalar Function

Numeric Function

SELECT ABS(-24) FROM DUAL; output: 24

SELECT POWER(5,2) FROM DUAL; output: 5*5 = 25

SELECT ROUND(16.966, 1) FROM DUAL; output: 17.0

SELECT SQRT(25) FROM DUAL; output: 5

SELECT EXP(2) FROM DUAL; output: 7.3890561

- this function calculates the value of ‘e’ to the power ‘argument’ where ‘ e = 2.71828183 ’ .

SELECT GREATEST(12, 20, 40) FROM DUAL; output: 40

SELECT LEAST(12, 20, 40) FORM DUAL; output: 12;

SELECT MOD(12,5) FROM DUAL; output: 12 divided by 5 and the answer is 2

SELECT CEIL(82.2) FROM DUAL; output: 83

SELECT FLOOR(82.2) FROM DUAL; output: 82

String Function

SELECT LOWER(‘PRAKHAR’) FROM DUAL; output: prakhar

SELECT UPPER(‘prakhar’) FROM DUAL; output: PRAKHAR

SELECT INITCAP(‘pRAKhar’) FROM DUAL; output: Prakhar

SELECT SUBSTR(‘prakhar’,2,5) FORM DUAL; output: rakha

- in above query, oracle will start reading from 2nd position up till ‘a’ which is at 5th position from there.

SELECT ASCII(‘A’) FROM DUAL; output: 65

SELECT INSTR(‘prakhar’, ‘a’) FROM DUAL; output: 3

SELECT INSTR(‘prakhar’, ‘a’, 1, 2) FROM DUAL; output: 6

-the above query will search for ‘a’ , it will start searching from the first occurrence of ‘a’ and it will search for the ‘a’ at second position.

SELECT TRANSLATE(‘prakhar’, ‘ar’ , ‘bs’) FROM DUAL; output: psbkhbs

SELECT LENGTH(‘cow’) “Length Of String” FROM DUAL; output: 3

SELECT LTRIM(‘prakhar’ , ‘pr’ ) FORM DUAL; output: akhar

-if no argument is passed i.e. in this case ‘pr’ , by default it will remove the white spaces from the starting.

SELECT RTRIM(‘prakhar’, ‘khar’) FROM DUAL; output: pra

SELECT TRIM(‘ prakhar ’) AS “TRIM” FROM DUAL; output: prakhar

SELECT TRIM(LEADING ‘X’ FROM ‘XXXprakharXXX’ ) FROM DUAL;

output: prakharXXX

SELECT TRIM(TRAILING ‘X’ FROM ‘XXXprakharXXX’ ) FROM DUAL;

output: XXXprakhar

SELECT TRIM(BOTH ‘X’ FROM ‘XXXprakharXXX’ ) FROM DUAL; output:

prakhar

SELECT LPAD(‘prakhar’ , 10, ‘*’) FROM DUAL; output: ***prakhar

SELECT RPAD(‘prakhar’ , 10, ‘*’) FROM DUAL; output: prakhar***

Conversion Function

SELECT 2 + TO_NUMBER(‘2’) FROM DUAL; output: 4

SELECT TO_CHAR(12345, ’00,0000’) FROM DUAL; output: 01,2345

- argument passed in the above query ‘12345’ is the input and ’00,0000’ this is the format we expect in our output.

SELECT TO_CHAR(SYSDATE, ‘MONTH DD YYYY’) AS “Date” FROM DUAL; output: March 24 2015

SELECT TO_CHAR(SYSDATE, ‘MM DD YYYY’) AS “Date” FROM DUAL; output: 03 24 2015

- in the above 2 queries the argument which we have passed the first one represents input date, and second one is for the format which we expect.

SELECT TO_DATE(SYSDATE, ‘DD MM YYYY’) “TO DATE” FROM DUAL; output: 24-03-2015

Date Function

- in oracle there are some function defined, with the help of them we can perform various tasks upon the values whose type is ‘DATE’.

SELECT ADD_MONTHS(SYSDATE, 6) “Add Month” FROM DUAL; input: 24-MAR-15 output: 24-SEP-15

- the argument passed in the above question, the first one represents the input date and the second one represents no. of months to be added to that current date.

SELECT LAST_DAY(SYSDATE) “Last Day” FROM DUAL; input (SYSDATE): 24-MAR-15 output: 31-MAR-15

SELECT NEXT_DAY(’24-MAR-15’, ‘monday’) FROM DUAL; output: 30-MAR-15

- the above function needs two arguments first one is the date and second one is day.

- this function helps us to find the date which will occur on the inputted day, and the date will be after ‘24-MAR-15’ i.e. the inputted date in above case.

SELECT MONTHS_BETWEEN( ‘06-JAN-16’ , ’06-APR-15’) FROM DUAL; output: 1

- the above function requires two arguments which are date, and this function will find out the months between these two dates.

SELECT TO_CHAR(SYSDATE, ‘DDTH/MM/YY’) FROM DUAL; output: example - 24TH/MAR/15

SELECT TO_CHAR(SYSDATE, ‘DDSP/MM/YY’) FROM DUAL; output: example – twenty-four/MAR/15

SELECT TO_DATE(’24/03/2015’, ‘DD/MM/YYYY’) FROM DUAL; output: 24-MAR-15

- in the above query the first argument is the string date which we want to cast in date formant, the second argument is to tell the function that in which format we are sending the date.

This is COMPANY table and Grouping

functions are applied on it

COMPANY AMOUNT

Tcs 12000

Tcs 20000

Hp 40000

Hp 30000

TABLE NAME = COMPANY

SELECT COMPANY, SUM(amount) FROM COMPANY WHERE COMPANY = ‘Hp’ GROUP BY COMPANY;

- In the above query the table name and the first column name are both ‘COMPANY’

- The output of the query will be executed in a manner such that all the rows with the company name ‘Hp’ will collapse and become one and all the data in the amount column against ‘Hp’ will be added together.

SELECT COMPANY, SUM(amount) FROM COMPANY GROUP BY COMPANY HAVING SUM(amount)>4000;

- We use ‘HAVING’ clause in a situation where we need further filtration on a result.

- In the above query the ‘group by’ clause will generate a result and the ‘having’ clause will provide further filtration on it.

output : Hp 70000

Joins, Sub-queries, and Views

Example table to understand joins

employees Table (j.1) orders Table (j.2)

emp_id (pk) emp_name

E01 Pandey sunil

E02 Dubey ajay

E03 Dubey anand

E04 Singh ashwin

prod_id

(pk)

prod_name emp_id

(fk)

234 Printer E01

657 Table E03

865 Chair E03

Inner Join

Inner join is used for handling complex data. When we need to extract the data from multiple tables then ‘inner join’ keyword is used.

SELECT e.emp_name, o.prod_name FROM orders o INNER JOIN employees e ON e.emp_id = o.emp_id;

-output:

1- pandey sunil printer

2- dubey anand table

3- dubey anand chair

- the above query can also be formed this way.

SELECT employees.emp_name, orders.prod_name FROM orders INNER JOIN employees ON employees.emp_id = orders.emp_id;

Right Join

This join works in a way that, the output of the query with right join will contain all the rows

that are present in the table whose name is written on the right side of this keyword.

SELECT e.emp_name, o.prod_name FROM orders o RIGHT JOIN employees e ON

e.emp_id = o.emp_id;

-output:




4- singh ashwin

5- dubey ajay


SELECT employees.emp_name, orders.prod_name FROM orders INNER JOIN

employees ON employees.emp_id = orders.emp_id;

Left Join

This join works in a way that, the output of the query with left join will contain all the rows

that are present in the table whose name is written on the left side of this keyword.

SELECT e.emp_name, o.prod_name FROM orders o LEFT JOIN employees e ON

e.emp_id = o.emp_id;

-output:





SELECT employees.emp_name, orders.prod_name FROM orders LEFT JOIN

employees ON employees.emp_id = orders.emp_id;

Self Join table( j.3 )

Id Name Type

1 Teacher 1

2 Student 1 0

3 Student 2 0

- Let this table name be “persons”

- In self join we treat one single table as two different table.

- All the columns in this table and all the example tables have data type VARCHAR2(10).

SELECT teacher.name “Teacher Name”, student.name “Student” FROM persons teacher, person student where student.type=‘0’ and teacher.type=‘1’;

-output:

Teacher Name Student Name

1 Teacher Student 1

2 Teacher Student 2

Cross Join

Sr_No Course_Name

1 BCA

2 BSC

Table: courses

Sr_no Sub_Name

1 oracle

2 java

Table: subjects

SELECT c.course_name, s.subject_name FROM courses c CROSS JOIN subjects s;

SELECT courses.course_name, subjects.subject_nameFROM courses CROSS JOIN subjects;

Output:

1. BSC oracle

2. BSC java

3. BCA oracle

4. BSC java

Sub-Queries

- We will use table ‘j.1’ and table ‘j.2’ to create a example showing how to use sub queries.

SELECT * FROM orders WHERE emp_idIN (SELECT emp_id FROM employees WHERE emp_name=‘Pandey sunil’);

output:

234 printer E01

UNION and UNION ALL

- UNION helps us to take out records from multiple tables and join them.

- The records that are present in the output, there can be multiple similar records but since we are using ‘UNION’ only single set of the total records will be displayed or we can say there will be no similar records in the output.

- Just like UNION, UNION ALL is used the basic difference between them is that, when we use UNION no duplicate record is displayed. Well in the case of UNION ALL, all the outputs which are generated by the individual query are displayed. We will see repetition of records while using UNION ALL clause.

- Using table (j.1) and (j.2) we will query on these table to understand ‘union’ and ‘union all’ more effectively.

SELECT emp_id FROM employees UNION SELECT emp_id FROM

orders;

SELECT emp_id FROM employees UNION ALL SELECT emp_id

FROM orders;

UNION query output UNION ALL query output

Emp_id

E01

E02

E03

E04

Emp_id

E01

E02

E03

E04

E01

E03

E03

INTERSECT

SELECT emp_id FROM employees INTERSECT SELECT emp_id FROM orders;

- the only records which are common in both the table will be show as the output of the above query.

output:

right side.

Emp_id

E01

E03

MINUS

SELECT emp_id FROM employees MINUS SELECT emp_id FROM orders;

- the output of the above query will contain all the emp_id’s which are present in the employees table but not in the orders table.

- if we swap places of both the table name in the above query the output will have no records to display, because order table have emp_id (1, 3) where as in employees (1,2,3,4).

Emp_id

E02

e04

VIEWS

They are used for security purposes, so that each column of a table can only be seen by those who are authorized to see it.

If for each user we define part-of a particular table so that he can see only those columns which they are allowed to, the redundancy will increase and this sort of approach is inefficient, but have the capability to provide security.

View don’t have data stored in them. They read the table and also read there own implementation so as to know, what are all the columns the need to show to the user.

We can use views as if they are tables, we can perform CRUD queries.

Views are of 2 types READ-ONLY and UPDATABLE.

CREATE , SELECT and INSERT

CREATE VIEW <view_name> AS SELECT <col_name> “<alias_name>”, <col_name 1> “<alias_name 1>” ,….FROM <table_name>;

SELECT <alias_name>, <alias_name1>, … FROM <view_name>;

INSERT INTO <view_name> values (‘<value>’, ‘<value>’);

UPDATE <view_name> SET <alias_name> = ‘<value>’ WHERE <alias_name?> = ‘<value>’;

DELETE FROM <view_name> WHERE <alias_name?>=‘<value>’;

DROP VIEW <view_name>;

Limitations (updatable view)

- Aggregate functions cannot be used.

- DISTINCT, HAVING, GROUP BY clause cannot be used.

- Sub queries cannot be used.

- UNION, INTERSECT and MINUS cannot be used.

- Constant, Strings and Expressions.

If one view is defined by another the other view must be

updatable.

oracle basic queries

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