COLUMN FUNCTIONS (AGGREGATE FUNCTIONS)
Aggregate functions allow you to calculate values based upon all data in an attribute of a table. The SQL aggregate functions are: Max, Min, Avg, Sum, Count, StdDev, Variance. Note that AVG and SUM work only with numeric values and both exclude NULL values from the calculations.
NOTE: COUNT can be used in two ways. COUNT(*) is used to count the number of tuples that satisfy a query. COUNT with DISTINCT is used to count the number of unique values in a named column.
1. Example 1
How many students are there? SELECT COUNT(*) FROM STUDENT;|
COUNT(*) |
|
6 |
2. Example 2
Find the number of departments that have faculty in them. SELECT COUNT(DISTINCT DEPT) FROM FACULTY;|
COUNT(DISTINCT) |
|
4 |
3. Example 3
Find the average number of credits for students who major in math. SELECT AVG(CREDITS) FROM STUDENT WHERE MAJOR = 'Math';|
AVG(CREDITS) |
|
29 |
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