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Databases Querying Relational Databases Subqueries Review and Practice

Posted by Wael Elsisi
Wael Elsisi
211 Points

How to use Subqueries ?

According to the video ,When use Subqueries, it only use to return only one column inside inner query. That mean I cannot use Subqueries to return maluti columns ?

What do you mean by "need a temporary dataset to join with other tables in your database." ?

1 Answer

Steven Parker
Steven Parker
229,759 Points
Steven Parker
Steven Parker
229,759 Points

At 00:49, when the video says "the subquery can only return one column", they don't mean that a subquery is limited to just one column, but that you can choose to have it do so when it fits your needs. A better comment might have been to say "the subquery can be made to only return one column". A subquery can return any number of columns, but often the situation requires just one.

I couldn't find your other quote in the video, but perhaps you meant at 00:29 where we hear "Or when you need to create a temporary data view, that you can join to other data elsewhere in your database." If so, by my understanding that just means the situation makes using a subset or aliased view of a table preferable to using the entire original table for joining.