& concept explained easily

1. Introduction to 1
SQL Group Functions

2. Introduction to 2
Chapter Objectives
• Differentiate between single-row and multiple-row
functions
• Use the SUM and AVG functions for numeric
calculations
• Use the COUNT function to return the number of
records containing non-NULL values
• Use COUNT(*) to include records containing
NULL values

3. Introduction to 3
Chapter Objectives
• Use the MIN and MAX functions with non-
numeric fields
• Determine when to use the GROUP BY
clause to group data
• Identify when the HAVING clause should
be used
• List the order of precedence for evaluating
WHERE, GROUP BY, and HAVING
clauses

4. Introduction to 4
Chapter Objectives
• State the maximum depth for nesting group
functions
• Nest a group function inside a single-row
function
• Calculate the standard deviation and
variance of a set of data, using the
STDDEV and VARIANCE functions

5. Introduction to 5
Group Functions
• Return one result per group of rows
processed
• Also called multiple-row and aggregate
functions
• All group functions ignore NULL values
except COUNT(*)
• Use DISTINCT to suppress duplicate
values

6. Introduction to 6
SUM Function
Calculates total amount stored in a numeric
column for a group of rows

7. Introduction to 7
AVG Function
Calculates average of numeric values in a
specified column

8. Introduction to 8
COUNT Function
Two purposes:
– Count non-NULL values
– Count total records, including those with NULL
values

9. Introduction to 9
COUNT Function –
Non-NULL Values
Include column name in argument to count
number of occurrences

10. Introduction to 10
COUNT Function –
NULL Values
Include asterisk in argument to count
number of rows

11. Introduction to 11
MAX Function
Returns largest value

12. Introduction to 12
MIN Function
Returns smallest value

13. Introduction to 13
GROUP BY Clause
• Used to group data
• Must be used for individual column in the
SELECT clause with a group function
• Cannot reference column alias

14. Introduction to 14
GROUP BY Example

15. Introduction to 15
HAVING Clause//
Serves as the WHERE clause for grouped
data

16. Introduction to 16
Order of Clause Evaluation
When included in the same SELECT
statement, evaluated in order of:
– WHERE
– GROUP BY
– HAVING

17. Introduction to 17
Nesting Functions
• Inner function resolved first
• Maximum nesting depth: 2

18. Introduction to 18
Statistical Group Functions
• Based on normal distribution
• Includes:
– STDDEV
– VARIANCE

19. Introduction to 19
STDDEV Function
Calculates standard deviation for grouped
data

20. Introduction to 20
VARIANCE Function
Determines data dispersion within a group