SQL/ SEARCHING 按ClassId查询

 ST_NAME  || ST_ID  || CLASS_ID || CLASS_INFO ---------------------------------------------  MARK || 1 || 100 || MATH YEN || 2 || 101 || CHEM SALLY || 3 || 100 || MATH SARA || 4 || 103 || HIST 
正确解法：

create table test(st_name varchar, st_id int, class_id int, class_info int); insert into test values('MARK', 1, 100, 'MATH'); insert into test values('YEN', 2, 101, 'CHEM'); insert into test values('MARK', 3, 100, 'MATH'); insert into test values('MARK', 4, 103, 'HOST'); SELECT (MAX(counter) > 1) as sameClass FROM (SELECT COUNT(st_id) counter FROM test WHERE ST_ID IN (1,2) GROUP BY class_info); SELECT (MAX(counter) > 1) as sameClass FROM (SELECT COUNT(st_id) counter FROM test WHERE ST_ID IN (1,2,3) GROUP BY class_info);