Learning SQL Command, SQL-Master.net
SQL command dictionary for beginners. Provide both command examples and results.
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AVG function is used to calculate an average value from a selected field.
Example1: Calculate an average value of employees’ salary.
SELECT AVG(salary) FROM tbSalaryTable;
| AVG(salary) |
| 254000 |
Example2: Calculate an average value of salary by each department.
SELECT deptCD, AVG(salary) FROM tbSalaryTable GROUP BY deptCD;
| deptCD | AVG(salary) |
| 100 | 150000 |
| 200 | 203090 |
| 300 | 403200 |
| 400 | 305420 |
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COUNT function to count number of rows
COUNT function is used to count a number of rows. If you want to count only unique elements, you can use DISTINCT to exclude duplicated elements. Example 1: count a number of employees SELECT COUNT(*) FROM tbEmpTable; COUNT(*) 24 Example 2: count numbers of employees by each department. SELECT deptCD, COUNT(*) FROM tbEmpTable GROUP BY deptCD; deptCD COUNT(*) 100 3 200 10 300 7 400 4 Example 3: count a number of departments SELECT COUNT(DISTINCT deptCD) FROM tbEmpTable; COUNT(DISTINCT deptCD) 4