SQL/MX Glossary

Glossary
HP NonStop SQL/MX Glossary—523732-002
Glossary-14
grouped select
grouped select. A query that generates a single row in the result table by processing a set
of rows from the table produced by the FROM clause. The grouping is determined by a
GROUP BY clause, a set (or aggregate) function in the select list, or a grouped view in
the FROM clause. The SELECT operation can result in one group (if no GROUP BY
clause is specified) or a set of groups.
grouped view. A view defined with a query that contains a GROUP BY or HAVING clause
that is not a subquery, contains a set (or aggregate) function in the select list, or refers
to another grouped view in the FROM clause.
grouping column. A column specified in a GROUP BY clause.
H
hash join. A join algorithm that creates a hash table for the inner table and joins the outer
table by hashing each outer row and looking for matches in the hash table. In some
situations, this algorithm performs better than either the sort merge or nested join
algorithms.
hash partitioning. A method of distributing records among partitions based on a hash
function that results in partitions of approximately equal size even if you do not know
the range values. With hash partitioning, SQL/MX uses a hash function on the values
of the partitioning key, and each record is assigned to a partition based on the result.
Records are evenly distributed across the partitions. Compare with range partitioning.
heading. A column attribute that specifies one or more lines of text to appear at the top of a
column in MXCI query results.
histogram. A representation of a relationship in which each value of some dependent
variable corresponds to a range of values of the associated independent variable or
variables. SQL/MX provides a method for generating histograms that show how data is
distributed with respect to a column or a group of columns within a table. See also
histogram_intervals
histogram caching. The ability of the SQL/MX compiler, when enabled, to cache in
memory histograms for tables used in a particular query and reuse them later for
statements during the same session.
histogram_intervals. User metadata tables that contain logical (table and column level)
histogram statistics. The UPDATE STATISTICS statement is used to specify columns
or groups of columns within the source table, to generate logical statistics that are
stored in the HISTOGRAM and HISTINTS tables. The data in these tables can be
accessed by using the SELECT statement. See also histogram.
host identifier. A name used in a host program to identify a program element such as a
data item, paragraph, or section.