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Difference Between Hash Join & Merge Join
Merge Join :Oracle performs a join between two sets of row data using the mergejoin algorithm. The inputs are two separate sets of row data. Output isthe results of the join. Oracle reads rows from both inputs in analternating fashion and merges together matching rows in order togenerate output. The two inputs are sorted on join column.Hash Join :Oracle performs a join between two sets...
mvg_mca
- Mar 24th, 2010
A merge join basically sorts all relevant rows in the first table by the join key, and also sorts the relevant rows in the second table by the join key, and then merges these sorted rows.A hash join (...
Manoj Seemar
- Nov 2nd, 2007
Merge Joins Sort merge joins can be used to join rows from two independent sources. Hash joins generally perform better than sort merge joins. On the other hand, sort merge joins can perform better th...
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Difference between Optimizer=ALL_ROWS and Optimizer=CHOOSE
Choose - Choose either Rule based or Cost based depend on theavailability of statistics. If statistics is available on the table it usesCBO and if not it uses RBO. ALL_ROWS - Choose based optimization, statistics is needed. U couldpass as hint in ur query.But in the majority of cases with optimizer_mode=choose ( and with a goodstatistics ) the CBO will be able to find a good...
Manoj Seemar
- Nov 2nd, 2007
The OPTIMIZER_MODE initialization parameter establishes the default behavior for choosing an optimization approach for the instance.CHOOSEThe optimizer chooses between a cost-based approach and a rule...
