Database Query Using SQL_ip.docx

Database Query Using SQL
Lets do practical on DATABASE…

SORTING OUTPUT
By default records will come in the output in the same order in which it was
entered. Tosee the output rows in sorted or arranged in ascending or descending
order SQL provide ORDER BY clause. By default output will be ascending
order(ASC) to see output in descending order we use DESC clause with ORDER BY
.
Select * from emp order by name; (ascending order)
Select * from emp order by salary desc;
Select * from emp order by dept asc, salary desc;

AGGREGATEfunctions
Aggregate function is used to perform calculation on group of rows and return the
calculated summary like sum of salary,averageof salary etc.
Available aggregatefunctions are –
1. SUM()
2. AVG()
3. COUNT()
4. MAX()
5. MIN()
6. COUNT(*)

AGGREGATEfunctions
Select SUM(salary) from emp;
Output – 161000
Select SUM(salary) from emp where dept=‘sales’;
Output - 59000
Empno Name Dept Salary
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000

AGGREGATEfunctions
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000
Select AVG(salary) from emp;
Output – 32200
Select AVG(salary) from emp where dept=‘sales’;
Output - 29500

AGGREGATEfunctions
Select COUNT(name) from emp;
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000
Output – 5
Select COUNT(salary) from emp where dept=‘HR’;
Output - 1
Select COUNT(DISTINCT dept)from emp;
Output - 3

AGGREGATEfunctions
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000
Select MAX(Salary) from emp;
Output – 45000
Select MAX(salary) from emp where dept=‘Sales’;
Output - 35000

AGGREGATEfunctions
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000
Select MIN(Salary) from emp;
Output – 24000
Select MIN(salary) from emp where dept=‘IT’;
Output - 27000

AGGREGATEfunctions
1 Ravi Sales 24000
2 Sunny Sales 35000
3 Shobit IT 30000
4 Vikram IT 27000
5 nitin HR 45000
6 Krish HR
Select COUNT(*)from emp;
Output – 6
Select COUNT(salary) from emp;
Output - 5

count(*) Vs count()
Count(*) function is used to count the number of rows in query
output whereas count() is used to count values present in any
column excludingNULL values.
Note:
All aggregatefunction ignores the NULL values.

GROUP BY
GROUP BY clause is used to divide the table into logical groups and we can
perform aggregate functions in those groups. In this case aggregate function
will return output for each group. For example if we want sum of salary of each
department we have to divide table records.

Aggregate functions by default takes the entire table as a single group that’s why we are
getting the sum(), avg(), etc output for the entire table. Now suppose organizationwants the
sum() of all the job separately,or wants to find the average salary of every job. In this case
we have to logically divide our table into groups based on job, so that every group will be
passed to aggregate function for calculation and aggregate function will return the result for
every group.

Group by clause helps up to divide the table into logical groups based on any
column value. In those logically divided records we can apply aggregate
functions.For.E.g.
SELECT SUM(SAL) FROM EMP GROUP BY DEPT;
SELECT JOB,SUM(SAL) FROM EMP GROUP BY
DEPT;
SELECT JOB,SUM(SAL),AVG(SAL),MAX(SAL),COUNT(*) EMPLOYEE_COUNTFROM EMP;
NOTE :- when we are using GROUP BY we can use only aggregate function and the column
on which we are grouping in the SELECT list because they will form a group other than any
column will gives you an error because they will be not the part of the group.
For e.g.
SELECT ENAME,JOB,SUM(SAL) FROM EMP GROUP BY JOB;
Error -> because Ename is not a group expression

HAVING with GROUP BY
• If we wantto filter or restrict some rowsfrom the output produced by GROUP BYthen we use HAVING
clause. It is used to put condition of group of rows. With having clause we can use aggregatefunctions
also.
• WHERE is used before the GROUP BY.With WHEREwe cannot use aggregatefunction.
• E.g.
• SELECT DEPT,AVG(SAL)FROM EMP GROUP BYDEPT HAVINGJOB IN (‘HR’,’SALES’
)
• SELECT DEPT,MAX(SAL),MIN(SAL),COUNT(*)FROM EMP GROUP BYDEPT HAVING
COUNT(*)>2
• SELECT DEPT,MAX(SAL),MIN(SAL)FROM EMP WHERE SAL>=2000 GROUP BYDEPT HAVING
DEPT IN(‘IT’,’HR’)

MYSQL FUNCTIONS
A function is built – in code for specific purpose that takesvalue and returns a
single value. Valuespassed to functions are known as arguments/parameters.
There are various categories of function in MySQL:-
1) String Function
2) Mathematical function
3) Date and time function

Function Description Example
CHAR() Return character for
given ASCII Code
Select Char(65);
Output- A
CONCAT() Return concatenated
string
Select concat(name, ‘ works in ‘, dept,’ department ’);
LOWER()/
LCASE()
Return string in small
letters
Select lower(‘INDIA’); Output- india
Select lower(name) from emp;
SUBSTRING(S,
P,N) /
MID(S,P,N)
Return N character of
string S, beginning from
P
Select SUBSTRING(‘LAPTOP’,3,3); Output – PTO
Select SUBSTR(‘COMPUTER’,4,3); Output – PUT
UPPER()/
UCASE()
Return string in capital
letters
Select Upper(‘india’); Output- INDIA
LTRIM() Removes leading space Select LTRIM(‘ Apple’); Output- ‘Apple’
RTRIM Remove trailing space Select RTRIM(‘Apple ‘); Output- ‘Apple’
String Function

TRIM() Remove spaces from
beginning and ending
Select TRIM(‘ Apple ‘); Output-’Apple’
Select* fromemp where trim(name) = ‘Suyash’;
INSTR() It search one string in
another string and
returns position, if not
found 0
SelectINSTR(‘COMPUTER’,’PUT’); Output-4
Select INSTR(‘PYTHON’,’C++’); Output – 0
LENGTH() Returns number of
character in string
Selectlength(‘python’); Output- 7 Select
name, length(name) fromemp
LEFT(S,N) Return N characters of S
from beginning
SelectLEFT(‘KV NO1 TEZPUR’,2); Output-KV
String Function

RIGHT(S,N) Return N characters of S
from ending
Select RIGHT(‘KV NO1 ’,3); Output- NO1

MOD(M,N) Return remainderM/N SelectMOD(11,5); Output- 1
POWER(B,P) Return B to power P SelectPOWER(2,5); Output-32
ROUND(N,D) Return number rounded to D
place after decimal
SelectROUND(11.589,2); Output- 11.59
SelectROUND(12.999,2); Output- 13.00
SelectROUND(267.478,-2) OUTPUT- 300
SIGN(N) Return -1 for –ve number 1 for
ve
+ number
Selectsign(-10) Output : -1
Selectsign(10); Output : 1
SQRT(N) Returns square rootof N SelectSQRT(144);Output: 12
TRUNCATE(M,
N)
Return number upto N place after
decimal without rounding it
SelectTruncate(15.789,2);Output: 15.79
Numeric Function

CURDATE()/
CURRENT_DATE()/
CURRENT_DATE
Return the current date Selectcurdate(); Select current_date();
DATE() Return date part from
datetime expression
Select date(‘2018-08-15 12:30’); Output:
2018-08-15
MONTH() Return month fromdate Selectmonth(‘2018-08-15’);Output: 08
YEAR() Return year fromdate Selectyear(‘2018-08-15’);Output: 2018
DAYNAME() Return weekday name Select dayname(‘2018-12-04’); Output:
Tuesday
DAYOFMONTH() Return value from1-31 Select dayofmonth(‘2018-08-15’) Output:
15
DAYOFWEEK() Return weekday index, for
Sunday-1, Monday-2, ..
Select dayofweek(‘2018-12-04’); Output:
3
Date and Time Function

DAYOFYEAR() Return value from1-366 Select dayofyear(‘2018-02-10’) Output:
41

Date and Time Function
NOW() Return both current date and time Select now();
at which the function executes
SYSDATE() Return both current date and time Select sysdate()
Difference Between NOW() and SYSDATE():
NOW() function return the date and time at which function was executed even if we
execute multiple NOW() function with select. whereas SYSDATE() will always return
date and time at which each SYDATE() function started execution. For example.
mysql> Select now(), sleep(2), now();
Output: 2018-12-04 10:26:20, 0, 2018-12-04 10:26:20
mysql> Select sysdate(), sleep(2), sysdate();
Output: 2018-12-04 10:27:08, 0, 2018-12-04 10:27:10

Database Query Using SQL_ip.docx

Database Query Using SQL_ip.docx

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