what is the difference between select single *
and slect upto 1 rows...
Answer Posted / gohila.r
Select Single * will pickup only one matching record from
the database into the buffer, and returns the same to the
internal table.
Select upto 1 rows will pickup all the records matching the
condition into the buffer, but return the top record to the
internal table.
For this reason, performance wise select upto 1 row is
better than select upto 1 row.
According to SAP Performance course the SELECT UP TO 1 ROWS
is faster than SELECT SINGLE because you are not using all
the primary key fields.
select single is a construct designed to read database
records with primary key. In the absence of the primary key,
it might end up doing a sequential search, whereas the
select up to 1 rows may assume that there is no primary key
supplied and will try to find most suitable index.
The best way to find out is through sql trace or runtime
analysis.
Use "select up to 1 rows" only if you are sure that all the
records returned will have the same value for the field(s)
you are interested in. If not, you will be reading only the
first record which matches the criteria, but may be the
second or the third record has the value you are looking for.
The System test result showed that the variant Single *
takes less time than Up to 1 rows as there is an additional
level for COUNT STOP KEY for SELECT ENDSELECT UP TO 1 ROWS.
The 'SELECT SINGLE' statement selects the first row in the
database that it finds that fulfils the 'WHERE' clause If
this results in multiple records then only the first one
will be returned and therefore may not be unique.
Mainly: to read data from
The 'SELECT .... UP TO 1 ROWS' statement is subtly
different. The database selects all of the relevant records
that are defined by the WHERE clause, applies any aggregate,
ordering or grouping functions to them and then returns the
first record of the result set.
Mainly: to check if entries exist.
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