oracle case when 语句

SELECT   grade, COUNT (CASE WHEN sex = 1 THEN 1      /*sex 1为男生，2位女生*/
                       ELSE NULL
                       END) 男生数,
                COUNT (CASE WHEN sex = 2 THEN 1
                       ELSE NULL
                       END) 女生数
    FROM students GROUP BY grade;

SELECT T2.*, T1.*
   FROM T1, T2
  WHERE (CASE WHEN T2.COMPARE_TYPE = 'A' AND
                   T1.SOME_TYPE LIKE 'NOTHING%'
                THEN 1
              WHEN T2.COMPARE_TYPE != 'A' AND
                   T1.SOME_TYPE NOT LIKE 'NOTHING%'
                THEN 1
              ELSE 0
           END) = 1

SELECT  
CASE WHEN salary <= 500 THEN '1'  
WHEN salary > 500 AND salary <= 600  THEN '2'  
WHEN salary > 600 AND salary <= 800  THEN '3'  
WHEN salary > 800 AND salary <= 1000 THEN '4'  
ELSE NULL END salary_class, -- 别名命名
COUNT(*)  
FROM    Table_A  
GROUP BY  
CASE WHEN salary <= 500 THEN '1'  
WHEN salary > 500 AND salary <= 600  THEN '2'  
WHEN salary > 600 AND salary <= 800  THEN '3'  
WHEN salary > 800 AND salary <= 1000 THEN '4'  
ELSE NULL END;  

select decode(sex, 'M', 'Male', 'F', 'Female', 'Unknown')
from   employees;

UPDATE HBBZ_2015_ALL SET pf=     
CASE  WHEN (trim(pfbz) in ('0','国0','国O','黄标0')) THEN '0'   
      WHEN (trim(pfbz) in ('1','国1','国I','国Ⅰ','黄标Ⅰ','绿标Ⅰ')) THEN '1'  
      WHEN (trim(pfbz) in ('2','国2','国II','国Ⅱ','黄标Ⅱ','黄标Ⅱ','绿标Ⅱ')) THEN '2'  
      WHEN (trim(pfbz) in ('3','国3','国III','国Ⅲ','绿标Ⅲ')) THEN '3' 
      WHEN (trim(pfbz) in ('4','国4','国IV','国Ⅳ','国Ⅳ','绿标Ⅳ')) THEN '4' 
      WHEN (trim(pfbz) in ('5','国5','国V','国Ⅴ','绿标Ⅴ')) THEN '5' 
      ELSE null END;
commit;

select fzjg,
--注销数
count(case when zxyy<>'M' and zxyy<>'P' and instr(zt,'P')=0 then 1 else null end) zs_zx,
count(case when zxyy<>'M' and zxyy<>'P' and instr(zt,'P')=0 and hbc is not null then 1 else null end) hbc_zx,
count(case when zxyy<>'M' and zxyy<>'P' and instr(zt,'P')=0 and hbc is not null 
    and ccdjrq < to_date('20060101','yyyymmdd') 
  and syxz in('B','C','D','E','F','G','N','R') then 1 else null end) hbc2005_zx from table_a group by fzjg order by fzjg;