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

SQL/MX Statements
HP NonStop SQL/MX Reference Manual—540440-003
2-40
CONTROL QUERY SHAPE Statement
MDAM_COLUMNS mdam-columns-option,...
specifies these MDAM_COLUMNS options:
n
specifies n key columns to be used by MDAM. For example, if MDAM is
using key columns specified by an index defined on a table, n specifies
that the first n columns listed in the index are used. The enumeration
algorithm for each column is determined by the system.
This option is the same as ALL if n exceeds the total number of columns
that MDAM can use.
SYSTEM
specifies that the system determines the number of key columns to be
used by MDAM on the basis of cost. The enumeration algorithm for each
column is determined by the system.
ALL
specifies that MDAM use all key columns. The enumeration algorithm for
each column is determined by the system.
(density,...)
specifies a list of enumeration algorithms. The density list forces which
algorithms MDAM uses for a set of key columns. If there are n algorithms
in the list, MDAM uses the first n key columns. If n exceeds the total
number of key columns, MDAM uses only the algorithms for the number of
available columns.
density is defined as:
SPARSE
specifies the use of the sparse algorithm for the column.
DENSE
specifies the use of the adaptive dense algorithm for the column.
SYSTEM
specifies that the system determines the enumeration algorithm for the
column on the basis of cost.
SYSTEM (density,...)
forces an enumeration algorithm to be used by MDAM for each key column
as determined by the density list. The system determines enumeration
algorithms for columns beyond those specified by the density list.