SQL查詢將三角形分類爲等邊，等腰等

Question

請告訴我這段代碼有什麼問題？ 我得到 「錯誤在第2行： ORA-00907：缺少右括號」爲下面的片段。請幫助我。

select (
IF (A = B or B = C or C = A) THEN 
DBMS_OUTPUT.PUT_LINE('Isosceles') 
ELSIF (A=B and B=c) THEN 
DBMS_OUTPUT.PUT_LINE('Equilateral') 
ELSIF (A != B) and (B != C) and (A+B>C or B+C>A or A+C>B)THEN 
DBMS_OUTPUT.PUT_LINE('Scalene') 
ELSE 
DBMS_OUTPUT.PUT_LINE('Not A Triangle') 
END IF 
) 
from triangles; 

Answer 1

請記住，CASE語句是爲了評估 - 第一個WHEN適合「獲勝」，並沒有進一步的評估條款作出。所以：

with 
    triangles (A, B, C) as (
     select 20, 20, 23 from dual union all 
     select 20, 20, 20 from dual union all 
     select 20, 21, 22 from dual union all 
     select 13, 14, 30 from dual 
    ) 
select A, B, C, 
     case 
      when A+B <= C or B+C <= A or C+A <= B then 'Not A Triangle'     
      when A = B and B = C    then 'Equilateral' 
      when A = B or B = C or A = C then 'Isosceles' 
      else          'Scalene' 
      end as classification 
from triangles 
; 

    A B C CLASSIFICATION 
--- --- --- -------------- 
20 20 23 Isosceles 
20 20 20 Equilateral 
20 21 22 Scalene 
13 14 30 Not A Triangle 

4 rows selected.