When I write the command select count(carga > 40) from cursos; what is the count logic that the count command is running?
This command worked in mysql however it returned me a result that I could not identify the source. I could not understand what the count identified on the basis.
count(expressao) does not fit what you're trying to do.
It returns no "true" or "false" account, but "how many instances of expressão are not null."
The count(*) is an exception, it returns all rows, regardless of nullity.
Manual:
Two solutions for you:
SELECT COUNT(*) FROM tabela WHERE carga > 40;
or
SELECT SUM(IF(carga > 40, 1, 0 ));
This second, with if , can be better understood in this post:
I would do it as follows
select count(*) from nometabela where carga > 40;
In this example it will count the records that were selected
The selected records would all be the carga value greater than 40
select count(carga) from nometabela where carga > 40;
If you put carga instead of * you may have problems if loading is null
Count () returns the line numbers. For example 5 records with load > 40 , then it will return 5.
To sum the value of the 5 registers for example use sum ().