Oracle SQL - Joins Syntax/Keywords

Question

When querying an Oracle DB:

If the query is a select with joins, does the syntax have to include the keywords:

• INNER JOIN
• OUTER JOIN
• LEFT/RIGHT OUTER JOIN

If not, then what are the alternative usages/syntax?

I ask this because I am looking at a SELECT statement that does not use any of the JOIN keywords within the FROM clause, but includes the joining syntax within the WHERE clause, and I am wondering:

• if the select is executing a JOIN
• if so, what kind of JOIN is it querying?

Example:

SELECT e.name, e.employeeid, d.sales, d.task, sum(d.hours)
FROM employee e,
       timecard d,
WHERE e.employeeid = d.employeeid and
GROUP BY ...
ORDER BY ...

Answer 1

That example is equivalent to an INNER JOIN. The equivalent (deprecated) syntax in Oracle for a LEFT join would be

SELECT e.name, e.employeeid, d.sales, d.task, sum(d.hours)
FROM employee e,
       timecard d,
WHERE e.employeeid = d.employeeid(+) and
GROUP BY ...
ORDER BY ...

Answer 2

Yes, this is a (inner) join, and could be rewritten as

SELECT e.name, e.employeeid, d.sales, d.task, sum(d.hours)
FROM employee e
JOIN timecard d on e.employeeid = d.employeeid
WHERE ...
GROUP BY ...
ORDER BY ...