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I am new to SQL and am trying to understand left join.

enter image description here

This is the diagram that I keep coming across when I search for left join. But what I fail to understand is the difference between left join and actually just selecting the whole left table, since they seem to be pretty much the same. After all, the highlighted area is just the entirety of the left table and nothing else.

I have tried looking for this answer, but all I keeping coming across are differences between inner and outer joins but not the answer to this particular question.

Thanks in advance for helping me out!

Chandra Sekhar Gudipati
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  • Just put this question out to help others in a similar position as me. Left join adds the values on the right table as well, with a null parameter. In other words, each row becomes longer. – Chandra Sekhar Gudipati Sep 16 '21 at 19:20
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    The related question/answer explains that the cardinality increases for the rows in the intersection area. In other words the rows in the middle section can show up more than once. – The Impaler Sep 16 '21 at 19:26

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