What's the difference of select single and select up to one row in ABAP

Select 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 t Hat there is no primary key supplied and would try to find most suitable index.

Use ' Select up to 1 rows ' only if is sure that the records returned would have the same value for the field (s) you is interested in. If not, you'll be reading only the first record which matches the criteria and may be the second or the third record ha s the value of you is looking for.

What's the difference of select single and select up to one row in ABAP