Oracle: What does `(+)` do in a WHERE clause?

Depending on which side of the “=” the “(+) is on, it denotes a LEFT OUTER or a RIGHT OUTER join (in this case, it’s a left outer join). It’s old Oracle syntax that is sometimes preferred by people who learned it first, since they like that it makes their code shorter.

Best not to use it though, for readability’s sake.

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