Sql代码
CREATE TABLE test(a VARCHAR2( 20),b VARCHAR2 (20),c NUMBER,d VARCHAR2 (20))
INSERT INTO test VALUES( \'a1\',\'b1\' ,1, \'t\');
INSERT INTO test VALUES( \'a3\',\'b3\' ,3, \'t\');
INSERT INTO test VALUES( \'a4\',\'b4\' ,4, \'t\');
INSERT INTO test VALUES( \'a2\',\'b2\' ,2, \'t\');
INSERT INTO test VALUES( \'xx\',\'xx\' ,5, \'x\');
INSERT INTO test VALUES( \'a1\',\'b1\' ,1, \'t\');
INSERT INTO test VALUES( \'a3\',\'b3\' ,3, \'t\');
INSERT INTO test VALUES( \'a4\',\'b4\' ,4, \'t\');
INSERT INTO test VALUES( \'a2\',\'b2\' ,2, \'t\');
INSERT INTO test VALUES( \'xx\',\'xx\' ,5, \'x\');
COMMIT;
1.SELECT a,b, SUM(c) FROM test WHERE d= \'t\' GROUP BY a,b ORDER BY a,b;
2.SELECT a,b, SUM(c) FROM test WHERE d= \'t\' GROUP BY b,a ORDER BY a,b;
总结:对于1,2而言,结果应该是一样的,但是分组的顺序不同,SQL的性能应该也是不同的。