#Oracle sql developer join full#

Internally Oracle translates these various joins into join methods to access the data. This syntax is generally not recommended any longer, as it has some limitations that the ANSI standard syntax does not have.īeware that there have been some bugs and performance with the ANSI syntax, although their number has decreased dramatically in more recent Oracle Database versions.įor a discussion on this topic we refer to this thread and the links provided therein. Oracle still supports the traditional syntax whereby the tables to be joined are all in the FROM clause, separated by commas, and join conditions are specified in the WHERE clause, either with or without the (+) notation. The CROSS APPLY is the equivalent of an inner lateral join, and OUTER APPLY does the same for outer lateral joins.Ī Cartesian product of two sets (i.e. ) syntax.Ī lateral view is “an inline view that contains correlation referring to other tables that precede it in the FROM clause”.

#Oracle sql developer join full#

) can be used as both an inner and a full join.Īs of 12c there is also a left lateral join, which can be employed with the LATERAL (. The former is a variation on the CROSS JOIN, whereas the latter is a variation on the LEFT JOIN. , but also some more exotic options that were introduced in 12c and are mainly interesting for people migrating from Microsoft SQL Server: CROSS APPLY (. and NATURAL JOIN syntax alternatives.įor the outer join we have LEFT JOIN. Table 1 illustrates the method of executing the query shown in the listing that follows when a HASH join is used.Probably the most used operation in a relational database is the infamous join.Īpart from the semi- and antijoin that are basically subqueries, which we have already seen, there are roughly two types of joins: the inner and the outer join. As with SORT-MERGE joins, HASH joins use memory resources and can drive up I/O in the temporary tablespace if the sort memory is not sufficient (which can cause this join method to be extremely slow).įinally, HASH joins are available only when cost-based optimization is used (which should be 100 percent of the time for your application running on Oracle 11g). The HASH join might be faster than a SORT-MERGE join, in this case, because only one row source needs to be sorted, and it could possibly be faster than a NESTED LOOPS join because probing a hash table in memory can be faster than traversing a b-tree index.Īs with SORT-MERGE joins and CLUSTER joins, HASH joins work only on equijoins. HASH joins can be effective when the lack of a useful index renders NESTED LOOPS joins inefficient. When using an ORDERED hint, the first table in the FROM clause is the table used to build the hash table. The HASH join is similar to a NESTED LOOPS join in the sense that there is a nested loop that occurs-Oracle first builds a hash table to facilitate the operation and then loops through the hash table. If you set the SGA_TARGET, you must set the PGA_AGGREGATE_TARGET as the SGA_TARGET does not include the PGA (unless you use MEMORY_TARGET as just described). If MEMORY_TARGET is used, the PGA_AGGREGATE_TARGET is included in the MEMORY_TARGET, but you may still want to set a minimum. Oracle uses a HASH join efficiently only if the parameter PGA_AGGREGATE_TARGET is set to a large enough value.

It then scans the other table in the join (usually the larger one) and probes the hash table for matches to it.

In a HASH join, Oracle accesses one table (usually the smaller of the joined results) and builds a hash table on the join key in memory. HASH joins are the usual choice of the Oracle optimizer when the memory is set up to accommodate them.