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A left outer join can usually be substituted for an inner join when the join columns in one table may contain NULL values. Any data column that may be NULL (empty) should never be used as a link in an inner join, unless the intended result is to eliminate the rows with the NULL value.
In SQL, a mere JOIN is equivalent to an INNER JOIN, the latter clarifying that the join statement is specifically an inner join operation as opposed to an outer join operation. Likewise, one may omit the OUTER from the LEFT OUTER JOIN, RIGHT OUTER JOIN and FULL OUTER JOIN.
The syntax of the SQL programming language is defined and maintained by ISO/IEC SC 32 as part of ISO/IEC 9075. This standard is not freely available. This standard is not freely available. Despite the existence of the standard, SQL code is not completely portable among different database systems without adjustments.
The right outer join of relations R and S is written as R S. [e] The result of the right outer join is the set of all combinations of tuples in R and S that are equal on their common attribute names, in addition to tuples in S that have no matching tuples in R. [citation needed] For example, consider the tables Employee and Dept and their right ...
I believe the example of how to construct a full outer join using only left joins is incorrect (the first one using outer left and outer right joins seems good). There is nothing ensuring that the two tables that are being unioned have the same column ordering.
In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. This can have major impact on performance because the correlated subquery might get recomputed every time for each row of the outer query is processed.
A right join is employed over the Target (the INTO table) and the Source (the USING table / view / sub-query)--where Target is the left table and Source is the right one. The four possible combinations yield these rules:
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