Question

Abap select single和select up to one row的区别

两者的异同点，最好详细点！

Answer 1

都是读取1行，结果没有什么区别，只是你在WHERE条件中如果指定了所有DB中的KEY的话建议用SELECT SINGLE，如果不全或是有大于小于之类的不能指定唯一性的判断条件的时候，建议用UP TO 1 ROWS，否则会在扩张检查的时候出现warning

Answer 2

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.

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.