In terms of SQL, what are the key differences between a left join, a right join, and a union?

Question

Anonymous · Accepted Answer

a left join will maintain all of the rows in the primary table and exclude the
rows from the table being joined if the join key does not have a corresponding
row in the primary table. a right join will do the opposite, keeping the rows
with a null in the primary table and excluding the primary table rows that do
not match in the joined table. A union is the concatenation of two outputs that
have the same exact columns. Joins are different from unions in that joined
tables are added as columns where unions are added as rows.

Anonymous · Answer

Left join = table on the left has all of it's records kept, even if there was
not a match. Nulls will be in the right table columns when there is no match

Right join = table on the right has all of it's records kept, even if there was
not a match. Nulls will be in the left table columns when there is no match

Union = Stack tables vertically. You need the same column names for both tables.
UNION removes duplicate rows, UNION ALL does not

In terms of SQL, what are the key differences between a left join, a right join, and a union?

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