Thank you, Dian.
You're right. When I was wondering about LEFT JOIN vs INNER JOIN, I was concerned not to end up with LEFT JOINS everywhere, in every query without proper understanding what I'm doing. I don't want to use LEFT JOIN just to be on the safe side, that some column in 'employees' table has NULL value in job_id field, for instance, and thus this employee is not included into overall result.
But you are right, that I need to take a look at the constraint of this field. If it is NOT NULL, so I can use INNER JOIN safely.
This, by the way, is an example when one should think about redesigning table constraints and, probably, adding NOT NULL constraints to important fields.
Thank you, once again for your time and comment. Honestly, I didn't think that anyone will read this post to the end and will grasp the idea of my questions.
Talking about the amount of data this query returns, this was a test task to see, if I'm able to join tables correctly. In real world, I'd prefer short queries which return specific data, not merging everything into one query. To my mind, it's more efficient.
Take care!
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Thank you, Dian.
You're right. When I was wondering about LEFT JOIN vs INNER JOIN, I was concerned not to end up with LEFT JOINS everywhere, in every query without proper understanding what I'm doing. I don't want to use LEFT JOIN just to be on the safe side, that some column in 'employees' table has NULL value in job_id field, for instance, and thus this employee is not included into overall result.
But you are right, that I need to take a look at the constraint of this field. If it is NOT NULL, so I can use INNER JOIN safely.
This, by the way, is an example when one should think about redesigning table constraints and, probably, adding NOT NULL constraints to important fields.
Thank you, once again for your time and comment. Honestly, I didn't think that anyone will read this post to the end and will grasp the idea of my questions.
Talking about the amount of data this query returns, this was a test task to see, if I'm able to join tables correctly. In real world, I'd prefer short queries which return specific data, not merging everything into one query. To my mind, it's more efficient.
Take care!