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B*Tree Reverse index

B*Tree Reverse index is one of the index types that is supported by oracle. It more or less behaves like b*tree unique & non-unique index but only difference is the way it constructs the tree. In this index, index value is stored in the reverse direction when compared to the values in the actual data table. This index is used in order to distribute the index data evenly across all the leaf index nodes if table data is skewed very high. Like b*tree index, this index doesn’t understand NULL. This B*Tree Reverse index can be created on a single column or more than one column. More than one B*Tree Reverse index can be created for the same data table. HOW TO VERIFY: How to verify whether the created index is reverse index or not? Fire this query, select index_type from user_indexes where index_name = 'DEPT_ID_INDX' ð This query would return “ NORMAL/REV ” (it means it is B*Tree index but of “Reverse” type) LITTLE-KNOWN FACTS TO BE REMEMBERED: · If this B*Tree Reve

Nested Loop Outer Join

Before we go into this topic in detail, first we will understand what outer join is meant by. For an example, take 2 tables which have to be joined, say “Parent” table & “Child” table [I have taken these table names, only to discuss this topic in an easy way]. If Child table is outer joined with Parent table, then you can say, the matching records from both these tables will be retrieved and then the records which are available only in Parent table will also be retrieved though the corresponding matching records are not available in Child table. This is called outer join. [in natural or equi-join, only the matching records from both the tables will be retrieved.] To perform this outer join, 3 different join techniques have been provided by oracle. · Nested loop outer join · Hash outer join · Sort merge outer join In this, we will discuss about nested loop outer join. To perform this nested loop outer join, Oracle follows these steps (assume, child ta

Index Fast Full Scan

Index Fast Full Scan is one of the index access methods supported by Oracle. Index Fast Full Scan is otherwise called as Fast Full Index Scan also. Index Fast Full Scan can be imposed by Oracle Optimizer only in the certain scenario. The scenario where this index would be invoked is, Whenever the Oracle SQL optimizer detects that the query is serviceable without touching table rows, Oracle invokes this fast full index scan and quickly reads every block of the index without touching the table itself provided that query doesn’t contain any ORDER BY clause. The definition for this scan is more or less similar to the index full scan but the only difference is that former will be invoked when ORDER BY clause is not mentioned in the query. It differs from the index full scan in another way where output won’t be in the sorted order since ORDER BY clause is not mentioned. If Oracle detects the query is serviceable without touching the table rows, it means, all the columns mentioned in th

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