Database Programming Using Oracle 11g

Database Programming Using Oracle 11g
Structured Query Language Recap

Structured Query Language Basics
Select Statement Its only known way to interact with Database to retrieve Data. Declarative Language DRL: Data Retrieval Language

Select distinct * | ColumnName from TableName; * mean all the column ColumnName is one or more column from table Distinct mean unique values from column

Select Statement Assumption is tables are created and data is populated

Implementing Select Statement

Select depno from emp; Select distinct deptno from emp; Select * from emp; Select ename, job from emp;

Select Statement Assumption is tables are created and data is populated

SQL and where clause Where clause is used to restrict number of rows Required rows can be fetch using Where clause Applied at each row of table

Select distinct * | ColumnName from TableName where condition 1 and / or condition 2 and / or condition 3 Conditions can include: >, <, =, <>, AND, OR, NOT

SQL and where clause If there are multiple conditions in where clause then at a time only one condition will be evaluated

Implementing Where Clause

Table Name: Emp Question # 1: Write a query to find out list of all those employee name who are earning more than 2500 but less than 5000. Question # 2: Write a query to find out all those employees who are working in Dept # 20 with designation of Analyst but not earning more than 2000 and was hired at least 30 years ago.

Table Name: Emp Question # 1: Write a query to find out list of all those employee name who are earning more than 2500 but less than 5000. Solution: Select ename from emp where sal>2500 and sal < 5000

Table Name: Emp Question # 1: Write a query to find out all those employees who are working in Dept # 20 with designation of Analyst but not earning more than 2000 and was hired at least 30 years ago. Solution: Select * from emp where deptno=20 and Job=‘Analyst’ and sal <2000 and hiredate<sysdate

Implementing Where Clause In where clause we have recap logical operators and comparison operators

Wild Cards Wild mean any character can be included Used for pattern matching to approximity

Wild Cards Two Wild Cards %: Zero or more characters - : Exactly one character

Implementing Wild Cards - I Wild Cards are implemented using LIKE Operator

Write a query to display list of name of all those employees who are having either E in the name or the name should end with G with at least two characters but should be working in Dept#30 and salary at least 1500 Solution: select * from emp where ename like '%E%' or ename like '%-G' and deptno=30 and sal >=1500;

Implementing Wild Cards - II

Write a query to display all information about all those employees who are having ER in the job with at least three character in job and should be earning at least 2500 but at most 5000 and should be with company for at most 15 years Select * from emp where job like ‘%ER-%’ and sal > 2500 and sal < 5000 and hiredate <=sysdate – 5600;

Single Row Functions Single row function operator in single row Return one result per row either Data or not Data

Round and Trunc : select round ( ,1), trunc( ,1) from dual; select ename, length(ename), instr (ename, 'A'), concat (ename,job) from emp where instr(ename,'A')=3; SELECT SUBSTR('ABCDEFG',3,4) "Substring" FROM DUAL;

Group Functions Group functions operate on multiple rows There is one row per group as output Group functions cannot be used in where clause

Implementing Group Functions-I

Write a query to display sum, minumum, maximum and average salaries which company is paying to its employees Solution: Select count(*), sum (sal), min(sal), max (sal), Avg(sal) from emp;

Implementing Group Functions-II

Write a query to display sum, minumum, maximum and average salaries which company is paying to its employees but employees from Dept# 20 should not be shown and average salaries should be less than 1500 Solution: Select count(*), sum (sal), min(sal), max (sal), Avg(sal) from emp where deptno !=20 and avg (sal) <=1500; - Error

Group By Clause Group by clause group together similar row together to form group Groups functions are used with Group by clause

Group By Clause After Select statement only those columns can be displayed which are written after Group-by clause

Implementing Group By Clause

What is the total salary paid by each department to its employees. Steps to Solution: i. Need to group together all rows of each department separately i-e creating groups ii. Need sum of salary each department - group

What is the total salary paid by each department to its employees. Solution select sum(sal), deptno from emp group by deptno; Column which is coming after Group by clause can only after select clause

Implementing Group By Clause-II

What is average and maximum salary paid to each Job who are reporting to MGR 7839 and all the emlpoyees should have no occurrence of K in their ename Solution -1 Select Avg(sal), max(sal) from emp where mgr=7839 and ename not like ('%K%') group by job;

What is average and maximum salary paid to each Job who are reporting to MGR 7839 and all the emlpoyees should have no occurrence of K in their ename Solution -2: Select Avg(sal), max(sal) , ename from emp where mgr=7839 and ename not like ('%K%') group by job; - Error : Only Job column can be shown after select

Having Clause To restrict groups having clause is used. Equivalent to Where clause except having is applied to groups only

Implementing Having Clause-I

Write a query to display average salary of each department if there are at least 2 employees working in the department and minimum salary is more than average salary by 100 Solution: Select avg (sal) from emp Group by deptno Having count (*) > 3 and min(sal)>avg(sal)+100;

Implementing Having Clause-II

Write a query to display maximum and minimum salary by each department if average salary is more than 1500 of the department and less than The employee should not be included if there is any occurrence of ‘A’ in the ename or earning no commission and is hired at least six month before

Select max(sal) , min(sal) from emp Where ename not like ‘%A%’ or comm is null and months_between(sysdate, hiredate)>6 Group by deptno Having max(sal) > 4500 and avg(sal)<1500;

Order by Clause Use to sort data Can use independent of where or group by or having clause

Select deptno, sal from emp order by sal;

What are Joins Joins are required when data from Multiple tables are required. No of Joins = No. Tables – 1 Comparison of PK and FK are implementation

Implementing Join-I

Basic Join Statement: Select empno,ename, d.deptno, dname from emp e, dept d where d.deptno=e.deptno;

Implementing Join-II

Write a query to display list of employee name and name of department of all those employees who are hired at least 10 years before and are working as Analyst Select empno,ename, d.deptno, dname, round(months_between(sysdate, hiredate),0), hiredate from emp e, dept d where d.deptno=e.deptno and months_between(sysdate, hiredate) > 120 and job=‘Analyst’;

What are Self Joins When PK and FK belong to same table Same tables are involved or written after from Used in recursive relationships

Implementing Self Join-I

select e.ename,e.empno, b.ename, b.empno from emp e , emp b, dept d where e.empno=b.mgr

Implementing Self Join-II

Write a query to display the employee name , employee number along with name and employee no of to whom it is reporting of all the employees who belong to accounting department

Solution select e.ename,e.empno, b.ename, b.empno from emp e , emp b, dept d where e.empno=b.mgr and d.deptno = b.deptno And dname = 'ACCOUNTING';

Subqueries Query within a query Select data from criteria which is developing on run-time Alternate to Joins

Subqueries A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved.

Implementing SubQuery - I

Write a query to display information of all those employees who are earning minimum salary but employees are neither working as Manager nor Clerk earning commission SELECT ename, sal, deptno FROM emp WHERE sal = (SELECT MIN (sal) FROM emp) and job <> ‘Manager’ and job !=‘CLERK’ and comm is not null;

Implementing SubQuery - II

Write a query to display all those deptno where minimum salary is less than average salary of all the salary among all the employee and location of department have at least 5 characters in it end with K

Solution: SELECT e.deptno, MIN (sal) FROM emp e, dept d Where d.deptno=e.deptno and loc like ('---K') GROUP BY e.deptno HAVING MIN (sal) < (SELECT AVG (sal) FROM emp);

Database Programming Using Oracle 11g

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