Chapter 2 grouping,scalar and aggergate functions,joins inner join,outer join
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This document provides an introduction to SQL server functions, grouping, and joins. It discusses aggregate functions that return single values from columns like average, sum, min, and count. It also discusses scalar functions that return a single value for each row like upper, lower, and round. The document explains how to use the GROUP BY clause to group result sets and then run aggregate functions on the groups. It also covers the HAVING clause, which filters grouped data. Finally, it describes different types of joins like inner joins, left outer joins, and right outer joins.
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Chapter 2 grouping,scalar and aggergate functions,joins inner join,outer join
- 1. Introduction to SQL server Grouping, Scalar and aggregate functions, Joins
- 2. SQL Functions • SQL has many built-in functions for performing calculations on data. It can be broadly classified in to two –Aggregate Functions – Scalar functions
- 3. SQL Functions • Aggregate Functions – SQL aggregate functions return a single value, calculated from all the values in a column. • Select AVG(int_price) from tbl_stock; // returns 8 • Select SUM(int_price) from tbl_stock; // returns 33 • Select MIN(int_price) from tbl_stock; // returns 2 • Select COUNT(vchr_product) from tbl_stock; // returns 4 Pk_int_id Vchr_product Int_price 1 Pen 10 2 Book 15 3 Eraser 2 4 Pencil 6 Tbl_stock Select SUM(int_price) from tbl_stock; Returns a single value
- 4. SQL Functions • Scalar Functions – SQL scalar functions return a single value for each values of a particular column given as input. ➢ Select UPPER(vchr_product) from tbl_stock; ➢ Select LOWER(vchr_product) from tbl_stock; ➢ Select ROUND(int_price) from tbl_stock; Pk_int_id Vchr_product Int_price 1 Pen 10 2 Book 15 3 Eraser 2 4 Pencil 6 Tbl_product Returns a value Returns a value Returns a value Returns a value
- 5. Grouping Data • GROUP BY allows you to take your result set, group it into logical groups and then run aggregate queries on the groups. • You could for instance select all employees, group them by their workplace location and calculate the average salary. This would give you the average salary of an employee at a given location in your database. Avg = 12500 Avg = 11500 Tbl_employee Emp_id Emp_name Emp_age Emp_email int_salary vchr_place 1000 Deepak 24 [email protected] 10000 Cochin 1001 Aneesh 23 [email protected] 20000 Calicut 1002 Naveen 25 [email protected] 15000 Cochin 1003 Jacob 25 [email protected] 13000 Calicut
- 6. Select vchr_place, avg(int_salary) from tbl_employee group by vchr_place; Example Result : Emp_id Emp_name Emp_age Emp_email int_salary vchr_place 1000 Deepak 24 [email protected] 10000 Cochin 1001 Aneesh 23 [email protected] 20000 Calicut 1002 Naveen 25 [email protected] 15000 Cochin 1003 Jacob 25 [email protected] 13000 Calicut Tbl_employee Vchr_place Avg(int_alary) Cochin 12500 Calicut 11500
- 7. The HAVING Clause • The HAVING clause was added to SQL because the WHERE keyword could not be used with aggregate functions. • An Sql statement can have both ‘where’ clause and ‘having’ clause. Where filters data before grouping.Having filters data after grouping • Syntax: • SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value;
- 8. Example Select vchr_place, avg(int_salary) from tbl_employee group by vchr_place having avg(int_salary)>12000; Vchr_place Avg(int_alary) Cochin 12500 Calicut 11500 Vchr_place Avg(int_alary) Cochin 12500
- 9. JOINS
- 10. Where do we use joins? • An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them. • Join helps to write single query to fetch data from multiple tables so as to meet the business requirement/generate reports
- 11. Types Of joins • Inner join • Outer Join – Left Outer Join – Right Outer Join
- 12. Inner Join • The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns in both tables. • Syntax – SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name=table2.column_name;
- 13. Pk_int_id Vchr_place 1 Mumbai 2 Kolkata 3 Bangalore 4 Cochin Emp_id Emp_name fk_int_place_id 1000 Deepak 1 1001 Aneesh 3 1002 Naveen 2 1003 Jacob 5 Emp_id Emp_name Vchr_place 1000 Deepak Mumbai 1001 Aneesh Banglore 1002 Naveen Kolkatta InnerJoin Inner Join SELECT emp_id,emp_name, vchr_place from tbl_employee Join tbl_place on fk_int_place_id=pk_int_id
- 14. Left Outer Join • The LEFT JOIN keyword returns all rows from the left table (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match. SELECT column_name(s) FROM table1 LEFT JOIN table2 ON table1.column_name=table2.column_name;
- 15. Left Outer Join Pk_int_id Vchr_place 1 Mumbai 2 Kolkata 3 Bangalore 4 Cochin Emp_id Emp_name fk_int_place_id 1000 Deepak 1 1001 Aneesh 4 1002 Naveen 2 1003 Jacob 5 1004 Alex 6 Emp_id Emp_name Vchr_place 1000 Deepak Mumbai 1001 Aneesh Cochin 1002 Naveen Kolkatta 1003 Jacob NULL 1004 Alex NULL LeftJoin SELECT emp_id,emp_name, vchr_place from tbl_employee Left Join tbl_place on fk_int_place_id=pk_int_id
- 16. Right Outer Join • The RIGHT JOIN keyword returns all rows from the right table (table2), with the matching rows in the left table (table1). The result is NULL in the left side when there is no match. SELECT column_name(s) FROM table1 RIGHT JOIN table2 ON table1.column_name=table2.column_name;
- 17. Right Outer Join Pk_int_id Vchr_place 1 Mumbai 2 Kolkata 3 Bangalore 4 Cochin 5 Trivandrum 7 Delhi Emp_id Emp_name fk_int_place_id 1000 Deepak 1 1001 Aneesh 4 1002 Naveen 2 1003 Jacob 5 1004 Alex 6 Emp_id Emp_name Vchr_place 1000 Deepak Mumbai 1001 Aneesh Cochin 1002 Naveen Kolkatta 1003 Jacob Trivandrum NULL NULL Banglore NULL NULL Delhi RightJoin SELECT emp_id,emp_name, vchr_place fromtbl_employee Right Join tbl_place on fk_int_place_id=pk_int_id
- 18. Questions? “A good question deserve a good grade…”
- 19. Self Check !!
- 20. Self Check !! • Scalar function will return 0 or more values –True –False
- 21. Self Check !! • Scalar function will return 0 or more values –True –False
- 22. Self Check !! • Round() is an aggregate function –True –False
- 23. Self Check !! • Round() is an aggregate function –True –False
- 24. Self Check !! • Spot out the errors Select dept,sum(salary), place from tbl_employee group by dept where sum(salary)>10000 Correct Answer: Select dept,sum(salary) from tbl_employee group by dept having sum(salary)>10000
- 25. Self Check !! • Spot out the errors Select dept,sum(salary), place from tbl_employee group by dept where sum(salary)>10000 Correct Answer: Result will be unexpected if display any columns without aggregate functions other than that given in group by Where must be given before group by We cannot use aggregate functions with where condition Select dept,sum(salary) from tbl_employee group by dept having sum(salary)>10000
- 26. Select id,student,dept from tbl_student join tbl_dept on fk_dept_id =pk_int_id Pk_int_id dept 1 Computer science 2 Electronics 3 Commerce 4 Art id Student fk_dept_id 1000 Ram 1 1001 Raju 4 1002 Mary 2 1003 Dona 5 1004 Lal 6 id Student dept 1000 Ram Computer science 1001 Raju Art 1002 Mary Electronics 1003 Dona NULL 1004 Lal NULL Query :
- 27. Select id,student,dept from tbl_student left join tbl_dept on fk_dept_id =pk_int_id Pk_int_id dept 1 Computer science 2 Electronics 3 Commerce 4 Art id Student fk_dept_id 1000 Ram 1 1001 Raju 4 1002 Mary 2 1003 Dona 5 1004 Lal 6 id Student dept 1000 Ram Computer science 1001 Raju Art 1002 Mary Electronics 1003 Dona NULL 1004 Lal NULL Query :
- 28. Self Check !! • When to use inner join – I want to display all the places and students from that places – I want to display all the students and their places – I want to display only the students of given places –I want to display the only students from places given in another table
- 29. Self Check !! • When to use inner join – I want to display all the places and students from that places – I want to display all the students and their places – I want to display only the students of given places – I want to display the only students from places given in another table
- 30. Self Check !! • When to use Right join A. Matching records from right table needs to be displayed B. Mismatching records from right table needs to be displayed C. Matching records from left table needs to be displayed D. Mismatching records from left table needs to be displayed E. Both A & B F. Both B & C
- 31. Self Check !! • When to use Right join A. Matching records from right table needs to be displayed B. Mismatching records from right table needs to be displayed C. Matching records from left table needs to be displayed D. Mismatching records from left table needs to be displayed E. Both A & B F. Both B & C
- 32. End of day 2
- 33. THANK YOU..