高手過招:用SQL解決環環相扣的刑偵推理問題(蘇旭輝版本)
蘇旭暉，網名 newkid，ITPUB 開發版資深版主，SQL開發專家
本文是繼 楊長老 刑偵高考：如何用SQL解決環環相扣的刑偵推理問題 之後，蘇旭輝的一個版本，希望大家能夠在高手的過招中，看到喜愛、堅持、執着與技藝。
試題再次如圖：
第一個解法如下：
with q as
(select 'A' c FROM DUAL
UNION ALL
SELECT 'B' FROM DUAL
UNION ALL
SELECT 'C' FROM DUAL
UNION ALL SELECT 'D' FROM DUAL)
,q2 as (
SELECT q1.c||q2.c||q3.c||q4.c||q5.c||q6.c||q7.c||q8.c||q9.c||q10.c s
,q7.c c7
,q10.c c10
FROM q q1,q q2,q q3,q q4,q q5,q q6,q q7,q q8,q q9,q q10
WHERE q2.c||q5.c IN ('AC','BD','CA','DB')
AND q3.c = CASE WHEN q3.c NOT IN (q6.c,q2.c,q4.c) THEN 'A'
WHEN q6.c NOT IN (q3.c,q2.c,q4.c) THEN 'B'
WHEN q2.c NOT IN (q3.c,q6.c,q4.c) THEN 'C'
WHEN q4.c NOT IN (q3.c,q6.c,q2.c) THEN 'D'
END
AND q4.c=CASE WHEN q1.c=q5.c THEN 'A'
WHEN q2.c=q7.c THEN 'B'
WHEN q1.c=q9.c THEN 'C'
WHEN q6.c=q10.c THEN 'D'
END
AND q5.c=DECODE(q5.c,q8.c,'A',q4.c,'B',q9.c,'C',q7.c,'D')
AND q6.c=DECODE(q8.c||q8.c,q2.c||q4.c,'A',q1.c||q6.c,'B',q3.c||q10.c,'C',q5.c||q9.c,'D')
AND ABS(DECODE(q8.c,'A',ASCII(q7.c)
,'B',ASCII(q5.c)
,'C',ASCII(q2.c)
,'D',ASCII(q10.c)
)-ASCII(q1.c))<>1
AND DECODE(q1.c,q6.c,1,-1) =- DECODE(DECODE(q9.c,'A',q6.c,'B',q10.c,'C',q2.c,'D',q9.c),q5.c,1,-1)
)
,q3 AS (SELECT q2.*,REGEXP_COUNT(s,'A') ca,REGEXP_COUNT(s,'B') cb,REGEXP_COUNT(s,'C') cc,REGEXP_COUNT(s,'D') cd FROM q2)
SELECT s
FROM q3
WHERE c7=DECODE(LEAST(ca,cb,cc,cd),cc,'A',cb,'B',ca,'C',cd,'D')
AND c10=DECODE(GREATEST(ca,cb,cc,cd)-LEAST(ca,cb,cc,cd),3,'A',2,'B',4,'C',1,'D')
;
S
----------
BCACACDABA
如果用1234取代ABCD，最後再變回來，那麼中間有些邏輯判斷可以用算術，代碼就更簡單：
with q as
(select LEVEL c FROM DUAL CONNECT BY LEVEL<=4)
,q2 as (
SELECT q1.c||q2.c||q3.c||q4.c||q5.c||q6.c||q7.c||q8.c||q9.c||q10.c s
,q7.c c7
,q10.c c10
FROM q q1,q q2,q q3,q q4,q q5,q q6,q q7,q q8,q q9,q q10
WHERE q2.c||q5.c IN ('13','24','31','42')
AND q3.c = CASE WHEN q3.c NOT IN (q6.c,q2.c,q4.c) THEN 1
WHEN q6.c NOT IN (q3.c,q2.c,q4.c) THEN 2
WHEN q2.c NOT IN (q3.c,q6.c,q4.c) THEN 3
WHEN q4.c NOT IN (q3.c,q6.c,q2.c) THEN 4
END
AND DECODE(q4.c,1,q1.c-q5.c,2,q2.c-q7.c,3,q1.c-q9.c,4,q6.c-q10.c)=0
AND q5.c=DECODE(q5.c,q8.c,1,q4.c,2,q9.c,3,q7.c,4)
AND q6.c=DECODE(q8.c||q8.c,q2.c||q4.c,1,q1.c||q6.c,2,q3.c||q10.c,3,q5.c||q9.c,4)
AND ABS(DECODE(q8.c,1,q7.c,2,q5.c,3,q2.c,4,q10.c)-q1.c)<>1
AND DECODE(q1.c,q6.c,1,-1) =- DECODE(DECODE(q9.c,1,q6.c,2,q10.c,3,q2.c,4,q9.c),q5.c,1,-1)
)
,q3 AS (SELECT q2.*,REGEXP_COUNT(s,'1') ca,REGEXP_COUNT(s,'2') cb,REGEXP_COUNT(s,'3') cc,REGEXP_COUNT(s,'4') cd FROM q2)
SELECT TRANSLATE(s,'1234','ABCD')
FROM q3
WHERE c7=DECODE(LEAST(ca,cb,cc,cd),cc,1,cb,2,ca,3,cd,4)
AND c10=DECODE(GREATEST(ca,cb,cc,cd)-LEAST(ca,cb,cc,cd),3,1,2,2,4,3,1,4)
;
TRANSLATE(S,'1234','ABCD')
-------------------------------------
BCACACDABA
SQL 的世界，精彩一如既往。