SQL/MX 2.x Reference Manual (H06.04+)

SQL/MX Statements
HP NonStop SQL/MX Reference Manual—540440-003
2-39
CONTROL QUERY SHAPE Statement
{SCAN | FILE_SCAN | INDEX_SCAN} [(scan-option,...)]
specifies the options that you can use with SCAN, FILE_SCAN, or INDEX_SCAN,
as follows:
TABLE table
specifies a table or correlation name. table is a character string literal—for
example, 't1'.
PATH {access-path | ANY}
access-path specifies an index name or the table name table. It is a
character string literal—for example, 'ix1' or 't1'. Use this option to force
the scan to be on that particular index or base table. The specified
access-path must cover all of the predicates defined on the table columns
for a plan to be generated.
ANY forces the scan to be on any available access path—an index or the base
table. In this case, the optimizer chooses the access path on the basis of cost.
If you do not use the PATH option, the default is ANY—except if the
MultiDimensional Access Method (MDAM) is forced, which changes the default
to the base table.
BLOCKS_PER_ACCESS value
specifies for the HP NonStop Data Access Manager (DAM) how many blocks
DAM can read ahead. DAM limits the number of read-ahead blocks to 14 at a
time. Use this token to control the read ahead in a mixed workload
environment to minimize its effect on other transactions. A setting of 1 (one)
prevents read ahead.
MDAM mdam-option,...
specifies MDAM options:
OFF
disables the MDAM option for this scan.
SYSTEM
specifies that the system determines whether to use MDAM on the basis of
cost.
FORCED
forces the use of MDAM for the scan. Using any MDAM_COLUMNS option
implies this option.