© Alex Reprintsev 2018Alex ReprintsevOracle SQL Revealedhttps://doi.org/10.1007/978-1-4842-3372-6_1
Most real-life queries combine data from multiple tables instead of querying a single table. Logic may be encapsulated in a view to hide complexity from the end user, but the database accesses multiple tables anyway to get the result set. It’s not necessary that data from all tables in a query appear in the result; some tables may be used to filter out data from other tables, for example.
Data from two tables may be combined using join (a join keyword is not mandatory as it will be shown later), subquery (may be correlated or not), lateral view (starting with Oracle 12c), or set operators (union/union all/intersect/minus). ...