COLLECT can be used to collect rows and insert them in an internal
table. If a row with the relevant primary key already exists in the target table, the values of numeric components are added to the values in the existing table row. Otherwise, a new row is inserted in the table.
Do not fill standard tables with collections of rows
Only use the statement
COLLECT for hashed tables or sorted tables with a unique key. Do not use it any more for standard tables.
COLLECT is based on unique entries with respect to the primary
key and stable key administration. This means that not all categories of internal ables are suitable for
- If the statement
COLLECTis applied to a standard table, this table first needs its own internal hash administration. Change operations on the table can invalidate this temporary hash administration. After a change operation of this type, the following
COLLECTstatements must resort to a linear search, which can affect performance considerably. The primary key of a standard table is also never unique.
COLLECTcan be used for sorted tables and hashed tables without any problems since these, unlike standard tables, always have a separate, stable key administration that can be utilized by
COLLECTcan work properly for sorted tables only if the primary key is unique. If a sorted table has a non-unique key, then only
COLLECTcan be used to fill the table, which is difficult to guarantee. In hashed tables, the key values are always unique.