Cluster Table is the another type of table which is supported by Oracle. A cluster is a schema object that contains one or more tables that all have one or more columns in common. Rows of one or more tables that share the same value in these common columns are physically stored together within the database. A cluster is to store data for more than 1 table in the same block. Tables which are created upon this cluster are called as “Cluster Table”. Cluster Index is an index which is created for this cluster. HOW TO VERIFY: How to verify whether the created table is “Cluster Table” or not? Fire this query, Select distinct cluster_name from user_all_tables where table_name IN ('EMPLOYEE',’DEPARTAMENT’) ð This query would return the name of the cluster (eg., query returns “CLUSTER_DEPT_ID” if it is the created cluster’s name) LITTLE-KNOWN FACTS TO BE REMEMBERED: · Clustered Index doesn’t occupy any memory space though it is creat...
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FBI is one of the index types that is supported by oracle. It more or less behaves like other type of b*tree indexes(unique,non-unique,reverse) but only difference is the way it builds the index table. In this, when it builds Index table, index value is derived by applying the user defined function on the table data. So, index data value and actual table data value would be different here. FBI is simply an index that uses the function so that the database can make direct comparisons between the index values and the filter values. This FBI index can be created on a single column or more than one column. More than one FBI can be created for the same data table but for the different columns. HOW TO VERIFY: How to verify whether the created index is FBI or not? Fire this query, select index_type from user_indexes where index_name = 'TOTAL_SAL_INDX' ð This query would return “ FUNCTION-BASED NORMAL ” (it means it is B*Tree index but of “FBI” type) LITTLE-KNOWN FACTS TO BE REM...
To perform hash join, Oracle follows these steps: 1. Oracle chooses the smallest of two tables as the hash table (otherwise called as driving table). Oracle built the hash table in RAM after applying the hash function on the joining column(s) of the driving table. 2. Oracle chooses the other [big] table as the probe table (otherwise called as driven table or probing table). It traverse through all the records of this probe table, applies the same hash function on the joining column(s) [column(s) used to join these two tables] and will hit the corresponding entry in the hash table. 3. Oracle returns the output if a record from driving table is already present in the same hash key, else no record will be returned. It may look like Nested loop join & Hash join have the same architecture since both these have the concept of driving & driven tables but they have entirely different design if you closely look a...
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