近幾天補oracle的sql知識，這塊記錄下sql的分組統計

1.簡單的分組統計

建立STUDENT表：

  CREATE TABLE STUDENT(
	"NAME" VARCHAR2(10 BYTE), 
	"MAJOR" VARCHAR2(10 BYTE), 
	"SCORE" NUMBER(5,2), 
	"SEX" VARCHAR2(3 BYTE)
   );

錄入資料：

Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (1,'邱君','語文',70,'女');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (2,'小狗','語文',76,'男');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (3,'混蛋','語文',60,'男');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (4,'邱君','數學',81,'女');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (5,'混蛋','數學',90,'男');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (6,'小狗','數學',77,'男');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (7,'邱君','外語',98,'女');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (8,'小狗','外語',71,'男');
Insert into STUDENT (ID,NAME,MAJOR,SCORE,SEX) values (9,'混蛋','外語',88,'男');
 

查詢語句（查找出有兩科分數大於80，並且平均平均成績大於80的同學）：

SELECT name,  
              SUM(CASE WHEN major = '數學' THEN score ELSE 0 END)數學 ,
              SUM(CASE WHEN major = '外語' THEN score ELSE 0 END)外語 ,
              SUM(CASE WHEN major = '語文' THEN score ELSE 0 END)語文, 
              AVG(score)
              FROM 
              student 
              GROUP BY NAME 
              HAVING 
              AVG(score) > 80 
              AND 
              SUM(CASE WHEN score > 80 THEN 1 ELSE 0 END) >= 2;
 

查詢結果：

 

2.group by 日期的處理：

select to_char(dt,'yyyy-mm-dd'),
      SUM(case when re='勝' then 1 else 0 end)勝,
      sum(case when re='負' then 1 else 0 end)負
      from
      test_tab
      group by to_char(dt,'yyyy-mm-dd')
      ;

to_char(date,'yyyy-mm-dd')處理日期，之後to_char(date,'yyyy-mm-dd')