This section is not intended to be a course in the SQL language. Hence, the focus will be put on the minimal set of differences that you must know in order to write queries properly.

...

select * from PROJECT

will work.

Whereas

select * from project

will not.

...

No schema names

Many database vendors group their tables into schemas (i.e.: PUBLIC). SQL Cloud does not support them.

...

SELECT `i`.`KEY`as `Issue`, count(*) as `Num. comments`
FROM ISSUE `i`
LEFT JOIN ISSUECOMMENT `ic` ON `ic`.`ISSUEID` = `i`.`ID`
WHERE `i`.`JQL` = 'PROJECT = TALH'
GROUP BY `i`.`KEY`
HAVING count(*) > 2

Works!

In this query the condition has been modified to uses column aliases: `Num. comments` > 2

SELECT `i`.`KEY`as `Issue`, count(*) as `Num. comments`
FROM ISSUE `i`
LEFT JOIN ISSUECOMMENT `ic` ON `ic`.`ISSUEID` = `i`.`ID`
WHERE `i`.`JQL` = 'PROJECT = TALH'
GROUP BY `i`.`KEY`
HAVING `Num. comments` > 2

Not works!

Subqueries are not supported

Use the WITH clause instead.