Session Level:
ALTER SESSION SET optimizer_goal= rule | first_rows | all_rows | choose ;
Hints:
- Hints always force the use of the cost based optimizer (Except RULE).
- Use ALIASES for the tablenames in the hints.
- Ensure tables are analyzed.
- Syntax: /*+ HINT HINT ... */ (In PLSQL the space between the '+' and
the first letter of the hint is vital
so /*+ ALL_ROWS */ is fine
but /*+ALL_ROWS */ will cause problems
)
- Optimizer Mode:
FIRST_ROWS, ALL_ROWS Force CBO first rows or all rows.
RULE Force Rule if possible
ORDERED Access tables in the order of the FROM clause
ORDERED_PREDICATES Use in the WHERE clause to apply predicates
in the order that they appear.
Does not apply predicate evaluation on index keys
- Sub-Queries/views:
PUSH_SUBQ Causes all subqueries in a query block to be
executed at the earliest possible time.
Normally subqueries are executed as the last
is applied is outerjoined or remote or joined
with a merge join. (>=7.2)
NO_MERGE(v) Use this hint in a VIEW to PREVENT it
being merged into the parent query. (>=7.2)
or use NO_MERGE(v) in parent query block
to prevent view V being merged
MERGE(v) Do merge view V
MERGE_AJ(v) } Put hint in a NOT IN subquery to perform (>=7.3)
HASH_AJ(v) } SMJ anti-join or hash anti-join. (>=7.3)
Eg: SELECT .. WHERE deptno is not null
AND deptno NOT IN
(SELECT /*+ HASH_AJ */ deptno ...)
HASH_SJ(v) } Transform EXISTS subquery into HASH or MERGE
MERGE_SJ(v) } semi-join to access "v"
PUSH_JOIN_PRED(v) Push join predicates into view V
NO_PUSH_JOIN_PRED(v) Do NOT push join predicates

- Access:
FULL(tab) Use FTS on tab
CACHE(tab) If table within <Parameter:CACHE_SIZE_THRESHOLD>
treat as if it had the CACHE option set.
See <Parameter:CACHE_SIZE_THRESHOLD>. Only
applies if FTS used.
NOCACHE(tab) Do not cache table even if it has CACHE option
set. Only relevant for FTS.
ROWID(tab) Access tab by ROWID directly
SELECT /*+ ROWID( table ) */ ...
FROM tab WHERE ROWID between '&1' and '&2';
CLUSTER(tab) Use cluster scan to access 'tab'
HASH(tab) Use hash scan to access 'tab'
INDEX( tab index ) Use 'index' to access 'tab'
INDEX_ASC( tab index ) Use 'index' to access 'tab' for range scan.
INDEX_DESC( tab index ) Use descending index range scan
(Join problems pre 7.3)
INDEX_FFS( tab index) Index fast full scan - rather than FTS.
INDEX_COMBINE( tab i1.. i5 )
Try to use some boolean combination of
bitmap index/s i1,i2 etc
AND_EQUAL(tab i1.. i5 ) Merge scans of 2 to 5 single column indexes.
USE_CONCAT Use concatenation (Union All) for OR (or IN)
statements. (>=7.2). See [NOTE:17214.1]
(7.2 requires <Event:10078>, 7.3 no hint req)
NO_EXPAND Do not perform OR-expansion (Ie: Do not use
Concatenation).
DRIVING_SITE(table) Forces query execution to be done at the
site where "table" resides
- Joining:
USE_NL(tab) Use table 'tab' as the driving table in a
Nested Loops join. If the driving row source
is a combination of tables name one of the
tables in the inner join and the NL should
drive off the entire row-source.
Does not work unless accompanied by an ORDERED
hint.
USE_MERGE(tab..) Use 'tab' as the driving table in a sort-merge
join.
Does not work unless accompanied by an ORDERED
hint.
USE_HASH(tab1 tab2) Join each specified table with another row
source with a hash join. 'tab1' is joined to
previous row source using a hash join. (>=7.3)
STAR Force a star query plan if possible. A star
plan has the largest table in the query last
in the join order and joins it with a nested
loops join on a concatenated index. The STAR
hint applies when there are at least 3 tables
and the large table's concatenated index has
at least 3 columns and there are no conflicting
access or join method hints. (>=7.3)
STAR_TRANSFORMATION Use best plan containing a STAR transformation
(if there is one)
- Parallel Query Option:
PARALLEL ( table, <degree> [, <instances>] )
Use parallel degree / instances as specified
PARALLEL_INDEX(table, [ index, [ degree [,instances] ] ] )
Parallel range scan for partitioned index
PQ_DISTRIBUTE(tab,out,in) How to distribute rows from tab in a PQ
(out/in may be HASH/NONE/BROADCAST/PARTITION)
NOPARALLEL(table) No parallel on "table"
NOPARALLEL_INDEX(table [,index])

- Miscellaneous
APPEND Only valid for INSERT .. SELECT.
Allows INSERT to work like direct load
or to perform parallel insert. See [NOTE:50592.1]
NOAPPEND Do not use INSERT APPEND functionality
REWRITE(v1[,v2]) 8.1+ With a view list use eligible materialized view
Without view list use any eligible MV
NOREWRITE 8.1+ Do not rewrite the query