ARTICLE
Selection of Table Type
What kind of table should be used in an individual case depends on the
type of individual row access that will be used most often on the table.
These rules are correspondingly relativized for tables with
secondary keys .
Standard Tables
This kind of table is appropriate when the individual entries can be
addressed using the index . Access via the index
is the fastest possible access to table entries. You should fill
standard tables by appending lines using APPEND
and implement the other accesses using an index specification (
INDEX addition of the respective statements). Since the cost of
accesses to standard tables via the primary key increases linearly with
the number of table entries, this type of access should only be used on
standard tables if the filling of the table can be separated from the
rest of the processing. If a standard table is sorted after filling, the
cost of a key access with a binary search (
BINARY SEARCH ) has a logarithmic relationship to the number of
table entries.
Sorted Tables
This kind of table is appropriate if the table must be sorted from the
time of creation. The filling of the table takes place by insertion
using the INSERT statement and in
accordance with the sort sequence defined by the primary table key. The
cost of key accesses is related logarithmically to the number of table
entries because a binary search is automatically carried out. Sorted
tables are also particularly suited for partially sequencial access in a
LOOP loop , if the first part of the
table key is specified in the WHERE condition.
Hashed Tables
This kind of table is suitable when key accesses are the central
operation to be carried out on the table. Hashed tables cannot be a
ccessed using a primary table index. However, the cost per key access is
always constant and independent of the number of table entries. As with
database tables, the key of hashed tables is always unique. Therefore
hashed tables are suitable for creating internal tables that are similar
to databases and can be used in a corresponding fashion.
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