Oracle SQL查询到GROUP BY并减去？

Question

如果我有四个列：表中的A，B，C和D，Oracle SQL查询将如何按列D进行分组，然后在每个分组中选择C ='c'的行，并为那些选定的行返回值B减去A？

Answer 1

SELECT Aggfunction(B - A), D FROM TABLENAME WHERE C='c' GROUP BY D

Replace Aggfunction with aggregate function you want eg SUM or AVG. You can only include ungrouped columns from a grouped sql query result set in an aggregate function (which makes sense because you only get one record out per group so have to accumulate the ungrouped columns in some way in order to represent a value per group)