"In" Relational Operator in SQL
"In" is used to find out if the value of a field is included in a specified list of values.
In the following statement we use "in" to find out if the value of the author field is included in the specified list of values (in this case, 2 strings).
Until now, to recover books whose author is 'Paenza' or 'Borges' we used 2 conditions:
select * from books
where author = 'Borges' or author = 'Paenza';
We can use "in" and simplify the query:
select * from books
where author in ('Borges', 'Paenza');
To recover books whose author is not 'Paenza' or 'Borges' we used:
select * from books
where author <> 'Borges' and
author <> 'Paenza';
We can also use "in" by prepending "not":
select * from books
where author not in ('Borges', 'Paenza');
Using "in" we find out if the value of the field is included in the specified list of values; with "not" preceding the condition, we invert the result, that is, we retrieve the values that are not found (do not match) with the list of values.
Values "null" are not considered.
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