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How MySQL evaluates when I use a conditional expression within SUM() function?
As we know that, by using a conditional expression within SUM() function we can get the number of rows that meet the condition. So, in this case, MySQL evaluates to 1 each time the condition is true and 0 each time it is false.
To understand it, consider the following example of table ‘employee’, having the following details −
mysql> Select * from Employee; +----+--------+--------+ | ID | Name | Salary | +----+--------+--------+ | 1 | Gaurav | 50000 | | 2 | Rahul | 20000 | | 3 | Advik | 25000 | | 4 | Aarav | 65000 | | 5 | Ram | 20000 | | 6 | Mohan | 30000 | | 7 | Aryan | NULL | | 8 | Vinay | NULL | +----+--------+--------+ 8 rows in set (0.00 sec)
Now, suppose if we want to know the total number of rows having a salary more than 20000 then the conditional expression can be used within SUM() function as follows −
mysql> Select SUM(Salary>20000) from employee568; +-------------------+ | SUM(Salary>20000) | +-------------------+ | 4 | +-------------------+ 1 row in set (0.00 sec)
The above result set shows that 4 employees are getting more than 20000 salaries.
Updated on: 22-Jun-2020
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