#Oracle pl sql developer interview questions and answers full#
Conceptually, a FULL JOIN combines the effect of applying both a LEFT JOIN and a RIGHT JOIN i.e., its result set is equivalent to performing a UNION of the results of left and right outer queries.ĬROSS JOIN: Returns all records where each row from the first table is combined with each row from the second table (i.e., returns the Cartesian product of the sets of rows from the joined tables). This means that if the ON clause doesn’t match any records in the left table, the JOIN will still return a row in the result for that record in the right table, but with NULL in each column from the left table.įULL JOIN (or FULL OUTER JOIN): Returns all rows for which there is a match in EITHER of the tables. This is the exact opposite of a LEFT JOIN i.e., the results will contain all records from the right table, even if the JOIN condition doesn’t find any matching records in the left table. RIGHT JOIN (or RIGHT OUTER JOIN): Returns all rows from the right table, and the matched rows from the left table. This means that if the ON clause doesn’t match any records in the right table, the JOIN will still return a row in the result for that record in the left table, but with NULL in each column from the right table. LEFT JOIN (or LEFT OUTER JOIN): Returns all rows from the left table, and the matched rows from the right table i.e., the results will contain all records from the left table, even if the JOIN condition doesn’t find any matching records in the right table. This is the default type of join if no specific JOIN type is specified.
“simple join”): Returns all rows for which there is at least one match in BOTH tables. ANSI-standard SQL specifies five types of JOIN clauses as follows: