The document explains the use of hints in Oracle databases to influence query optimization and execution plans. It details various types of hints, including access, join, and miscellaneous hints, along with examples of their application in SELECT, DELETE, and UPDATE statements. Furthermore, it outlines specific hints like 'all_rows', 'first_rows', 'full', and 'index', which help improve query performance by altering how the database processes them.

1. Presented By
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2.  Hints give specific information that we
know about our data and application.
 A way to override the default query
optimization in the DBMS
 Influence the execution plan of query
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3.  Oracle optimizer may not always choose
the best execution plan
 Using hints may improve the performance
by changing the execution plan oracle
takes.
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4.  Hints can be used in the Select, Delete, and
Update clauses.
 In each statement, the hint goes directly
after the Select, Delete, or Update
keyword. A few hints use Insert.
 Hints are placed in the /*+ */ tag, where
the hint goes after the + sign
 Ex: SELECT /*+ ALL_ROWS */ From…
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5.  Approach hints
 Access hints
 Join hints
 Misc. hints
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6.  ALL_ROWS: Minimizes total resource
consumption. Results will be returned
only after all processing has been
completed
 FIRST_ROWS(n): Minimized response
time, or minimal resource usage to return
the first n rows.
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7.  FULL(table): Chooses a full table scan for
the table, even if there is an index available.
 INDEX(table [index [index]...]): Chooses an
Index scan for the table.
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8.  CIS Department has far more males than
females
 SELECT /*+ FULL(s) */ id, name
FROM Student s
WHERE sex = ‘m’;
 SELECT /*+ Index(s sex_index) */ id, name
FROM Student s
WHERE sex = ‘f’;
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9.  ORDERED: tables are joined in the order in
which they appear in the FROM clause.
 LEADING(table): specified table is the first
table used in the join order.
 USE_HASH(table [table] …): Tables are
joined using a hash join. Smaller table is
used to make a hash table on join key. The
larger table is scanned using hash table to
find joined rows.
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10.  USE_NL(table [table]…): Joins tables using
nested loops join, using specified table as
inner join. For every row in outer table, oracle
accesses every row in inner table.
 USE_MERGE(table [table]…): Joins tables
using a sort-merge join. Sorted list are made
and then merged together. Best if tables are
already sorted.
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11.  APPEND: Data is appended to the end of table,
rather then using existing space.
 CACHE(table): Blocks received are placed at
the most recently used end of the LRU list in
the buffer cache when a full table scan is
preformed.
 NOCACHE(table): Blocks received are placed
at the least recently used end of the LRU list in
the buffer cache.
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12.  Oracle documentation at:
http://oracle.cis.ksu.edu/oradocs/index.htm
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