Editing Ingres (database) (section)

===Joins===
Ingres supports joins with hash join, sort-merge join, and nested loop join algorithms. The query optimizer determines which type of join algorithm to use based on its analysis of the query. Nested-loop joins are most often seen on disjoint queries, where correlation variables and table names are arbitrarily used in random order. When there are no restrictions on either table in the join clause, and the rows being joined are spatially continuous, then the query optimizer is likely to choose sort-merge join or hash join.<ref>{{cite web | url=http://docs.actian.com/ingres/10s/index.html#page/DatabaseAdmin%2FJoin_Nodes_in_a_QEP.htm%23 | title=Ingres }}</ref>