数据库编程大赛冠军：郑凌云：0.67秒通过百万级数据评测！SQL代码惊现神之一手！

12月27日，NineData和云数据库技术社区主办，华为云、火山引擎、开源中国、云和恩墨、TDengine、云猿生数据、DORIS、ITPUB等协办单位和媒体，共同举办了本次《数据库编程大赛》。大赛题目「用一条SQL给出扑克牌24点的计算表达式」。

以下冠军选手郑凌云的参赛情况的介绍：

参赛选手：郑凌云

个人简介：淘宝，负责推荐系统开发

参赛数据库：MySQL

性能评测：百万级数据代码性能评测 0.67秒

综合得分：95

以下是郑凌云选手的代码说明思路简介：

0. 核心：因为4张牌计算24点时的顺序可任意互换，所以不同排列的4张牌可视为同一组合。采用质数编码，把1到10映射成2到29内的质数，4张牌的积可作为该组合的唯一编码

1. 本地写代码，通过简单的回溯算法，生成24点游戏的所有解：152,((1+1)+1)*8,156,(6*2)*(1+1),...

2. 受限于代码大小10k限制，通过把上一步生成的数据进行压缩：SELECT REPLACE(TO_BASE64(COMPRESS('152,((1+1)+1)*8,156,(6*2)*(1+1),...')), '\n', '')

3. 提交的代码中，先对上一步生成的数据解压缩：UNCOMPRESS(FROM_BASE64('XXXX'))，并通过递归CTE生成查询表：152,((1+1)+1)*8;156,(6*2)*(1+1);...

4. 对输入表LEFT JOIN上一步生成的查询表，关联的键值是对c1，c2，c3，c4做质数编码后的积。

以下是郑凌云选手的算法说明，结尾附完整SQL：

算法说明

看到题目是用SQL算24点，感觉挺有意思的，平时使用SQL最多就是简单SELECT一下，从未想过是否可以算24点，就想挑战一下。

阶段一

结合题目条件，分析了一下这个24点游戏的问题。待求解的输入行数比较多，但4张1到10的牌的组合最多只有715种。在这个前提下，自然是先计算出715种组合的所有结果后，再进行LEFT JOIN。

先计算715种组合的结果

大概有两种思路：

1. 求解的方法

2. 构造的方法

求解的方法

即先遍历715种组合，通过回溯法计算每个组合的解（思路就是4个数算24，先4选2，进行加减乘除反向减反向除6种运算，问题化简为3个数算24；然后继续该过程直到最终化简为1个数算24，需要的计算量在4573左右），复杂度在 715 * 4573 = 327万左右。

构造的方法

4个数算24，本质上其实只有两种形式，即：

((a op b) op c) op d = 24

或者

(a op b) op (c op d) = 24

则可以构造出所有1到10的数字进行这两种形式计算，看结果是否能等于24。（可以这样理解：算24第一步肯定是2张牌进行计算；第二步则有两种选择，要么和第3张牌计算，要么和剩下的两张牌计算的结果进行计算）

其中还有两个优化点：

1. x op y （x和y是两张牌的原始点数，而不是计算结果）有两种算法：一是x和y都可以取1到10之间的数，op有加减乘除4种，那总共有400种（很明显其中有重复的）；二是限制y必须大于等于x，op有加减乘除反向减反向除6种，那总共有330种。我们会选择复杂度小的330种这种方式。

2. ((a op b) op c) op d = 24 这种形式，如果直接计算，复杂度在 330 * 6 * 10 * 6 * 10 = 119万左右，而如果从24反向计算回最后一个数，即 ((24 op d) op c) op b = a，其中a是1到10中的某整数，复杂度在 1 * 6 * 10 * 6 * 10 * 6 * 10 = 22万左右。我们选择复杂度小的22万种这种方式。

对于 (a op b) op (c op d) = 24 这种形式，复杂度约 330 * 6 * 330 / 2 = 33万左右（这个表达式是估算的，我没有进行严格计算）。两种形式加起来复杂度在55万左右，比第一种思路的复杂度327万会低很多。所以我们采用第二种思路。

再进行LEFT JOIN

JOIN需要一个关联条件，怎么唯一表示4个数的组合呢？可以排序，可以用带计数的map甚至bitmap，还可以用质数编码后的乘积表示。我采用了质数编码。其实bitmap或许性能更高，但需要一些精细的操作，我并没有去比较过这两种方式的性能区别（有兴趣的人可以试一下），当时也没有纠结，就选了更习惯的质数编码。因为在这个阶段我和很多人一样陷入到怎么求解24点的问题中，并没有意识到JOIN的关键。

SQL代码

WITH RECURSIVEoperations(op) AS (VALUES ROW(1), ROW(2), ROW(3), ROW(4), ROW(5), ROW(6)),numbers(val, enc) AS (VALUES ROW(1, 2), ROW(2, 3), ROW(3, 5), ROW(4, 7), ROW(5, 11), ROW(6, 13), ROW(7, 17), ROW(8, 19), ROW(9, 23), ROW(10, 29)),reverse_combinations1(enc, val, rst) AS (SELECT enc, val, 24e0 FROM numbers),reverse_combinations1_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | valWHEN 2 THEN (14 << 4) | valWHEN 3 THEN (val << 4) | 12WHEN 4 THEN (11 << 4) | valWHEN 5 THEN (val << 4) | 14WHEN 6 THEN (13 << 4) | valENDFROM reverse_combinations1 CROSS JOIN operations),reverse_combinations1_solution_faster AS (SELECT DISTINCT enc, rst, solution FROM reverse_combinations1_solution),reverse_combinations2(enc, val, rst, solution) AS (SELECT t1.enc * t2.enc, val, rst, solution FROM reverse_combinations1_solution_faster t1 CROSS JOIN numbers t2),reverse_combinations2_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | val | (solution << 8)WHEN 2 THEN (14 << 4) | val | (solution << 8)WHEN 3 THEN (val << 4) | 12 | (solution << 8)WHEN 4 THEN (11 << 4) | val | (solution << 8)WHEN 5 THEN (val << 4) | 14 | (solution << 8)WHEN 6 THEN (13 << 4) | val | (solution << 8)ENDFROM reverse_combinations2 CROSS JOIN operations),reverse_combinations2_solution_faster2x AS (SELECT DISTINCT enc, rst, solution FROM reverse_combinations2_solution),reverse_combinations3(enc, val, rst, solution) AS (SELECT t1.enc * t2.enc, val, rst, solution FROM reverse_combinations2_solution_faster2x t1 CROSS JOIN numbers t2),reverse_combinations3_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | val | (solution << 8)WHEN 2 THEN (14 << 4) | val | (solution << 8)WHEN 3 THEN (val << 4) | 12 | (solution << 8)WHEN 4 THEN (11 << 4) | val | (solution << 8)WHEN 5 THEN (val << 4) | 14 | (solution << 8)WHEN 6 THEN (13 << 4) | val | (solution << 8)ENDFROM reverse_combinations3 CROSS JOIN operations),reverse_combinations_solution(enc, solution) AS (SELECTenc *CASE ROUND(rst)WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END,ROUND(rst) | solution << 8FROM reverse_combinations3_solution WHERE (ROUND(rst) BETWEEN 1 AND 10) AND ABS(ROUND(rst) - rst) < 0.000001),reverse_combinations_solution_distinct(enc, solution) AS (SELECT enc, ANY_VALUE(solution) FROM reverse_combinations_solution GROUP BY enc),reverse_format_solution(enc, expr, solution) AS (SELECT enc, CAST((solution & 0x0F) AS CHAR), solution >> 8 FROM reverse_combinations_solution_distinctUNION ALLSELECT enc,CASE (solution & 0xF0) >> 4WHEN 11 THEN CONCAT('(', expr, '+', solution & 0x0F, ')')WHEN 12 THEN CONCAT('(', expr, '-', solution & 0x0F, ')')WHEN 13 THEN CONCAT('(', expr, '*', solution & 0x0F, ')')WHEN 14 THEN CONCAT('(', expr, '/', solution & 0x0F, ')')ELSECASE solution & 0x0FWHEN 12 THEN CONCAT('(', (solution & 0xF0) >> 4, '-', expr, ')')WHEN 14 THEN CONCAT('(', (solution & 0xF0) >> 4, '/', expr, ')')ENDEND,solution >> 8FROM reverse_format_solution WHERE solution > 0),reverse_solution(enc, expr) AS (SELECT enc, expr FROM reverse_format_solution WHERE solution = 0),combinations2(enc, c1, c2) AS (SELECT t1.enc * t2.enc, CAST(t1.val AS DOUBLE), CAST(t2.val AS DOUBLE)FROM numbers t1JOIN numbers t2 ON t1.val <= t2.val),combinations2_solution(enc, rst, expr) AS (SELECTenc,CASE opWHEN 1 THEN c1 + c2WHEN 2 THEN c1 * c2WHEN 3 THEN c1 - c2WHEN 4 THEN c2 - c1WHEN 5 THEN c1 / c2WHEN 6 THEN c2 / c1END,CASE opWHEN 1 THEN CONCAT('(', c1, '+', c2, ')')WHEN 2 THEN CONCAT('(', c1, '*', c2, ')')WHEN 3 THEN CONCAT('(', c1, '-', c2, ')')WHEN 4 THEN CONCAT('(', c2, '-', c1, ')')WHEN 5 THEN CONCAT('(', c1, '/', c2, ')')WHEN 6 THEN CONCAT('(', c2, '/', c1, ')')ENDFROM combinations2 CROSS JOIN operations),combinations2_solution_faster7x AS (SELECT DISTINCT enc, rst, expr FROM combinations2_solution),combinations4(enc1, enc2, rst1, rst2, expr1, expr2) AS (SELECT t1.enc, t2.enc, t1.rst, t2.rst, t1.expr, t2.exprFROM combinations2_solution_faster7x t1JOIN combinations2_solution_faster7x t2 ON t1.enc <= t2.enc),combinations4_faster2x AS (SELECT DISTINCT enc1, enc2, rst1, rst2, expr1, expr2 FROM combinations4),combinations4_solution(enc, rst, expr) AS (SELECTenc1 * enc2,CASE opWHEN 1 THEN rst1 + rst2WHEN 2 THEN rst1 * rst2WHEN 3 THEN rst1 - rst2WHEN 4 THEN rst2 - rst1WHEN 5 THEN rst1 / rst2WHEN 6 THEN rst2 / rst1END,CASE opWHEN 1 THEN CONCAT(expr1, '+', expr2)WHEN 2 THEN CONCAT(expr1, '*', expr2)WHEN 3 THEN CONCAT(expr1, '-', expr2)WHEN 4 THEN CONCAT(expr2, '-', expr1)WHEN 5 THEN CONCAT(expr1, '/', expr2)WHEN 6 THEN CONCAT(expr2, '/', expr1)ENDFROM combinations4_faster2x CROSS JOIN operations),solution(enc, expr) AS (SELECT enc, ANY_VALUE(expr) FROM combinations4_solution WHERE ABS(rst - 24) < 0.000001 GROUP BY enc),lookup_table(enc, result) AS (SELECT enc, ANY_VALUE(expr) FROM (SELECT enc, expr FROM solutionUNION ALLSELECT enc, expr FROM reverse_solution) t1 GROUP BY enc)SELECT id, c1, c2, c3, c4, resultFROM poker24.cardsLEFT JOIN lookup_table ON enc=CASE c1WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c2WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c3WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c4WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END

最后分析下性能

耗时：join(20ms) + 构造lookup_table(187ms) = 207ms

这里构造lookup_table的耗时，即为计算715种组合24点解的耗时。

阶段二

怎么更快地求解24点问题呢？因为前面计算出了结果，看了下其实只有566个答案，尝试直接把答案构造进SQL进行JOIN，发现超过了题目要求的10KB限制。我对SQL也不是很熟悉，一度放弃了该方案，直到发现MySQL中有COMPRESS()函数。。。

1. 通过 SELECT REPLACE(TO_BASE64(COMPRESS('152,((1+1)+1)*8,156,(6*2)*(1+1),...')), '\n', '') 把结果编码输出

2. 提交的代码中，先对上一步生成的数据解压缩：UNCOMPRESS(FROM_BASE64('XXXX'))，并通过递归CTE生成查询表：152,((1+1)+1)*8;156,(6*2)*(1+1);...

3. 对输入表LEFT JOIN上一步生成的查询表，关联的键值是对c1，c2，c3，c4做质数编码后的乘积

SQL代码v1

决采用拼接union select或values（）的长度超过10K字节限制的问题，主要采取了以下压缩空间的技巧：

WITH RECURSIVE lookup_table(enc,result,dat) AS(SELECT 0,'err_placeholder',UNCOMPRESS(FROM_BASE64('ICcAAHicTVpbkiMhDLvOTCZd4WUD97/YWpIhWzUf0zTY4Ics06nW3j8/9a/+xt9rvav5+8df7ffFwXcr4/0z8e6n8bktzH/F/Ib5bcb8/dz3fcT7Wv6ugDrK+2e8+hXY4tkosPPZy9mA/756CChHweTziucV6/9+aqh5D8zff1ee4X0tD5+woG4/Asfva7x7uTs2PvvACccViBPMhzPw3npYZGGtFPgY54QD81c9FnvVEjreY8UEe9mvZLxtxgQ7Av09YZIJ5RK4uus9N7zejg04Tq/3ey2c2H8/acHviV47rBQnnHcLM/xWwsjYpEbW71+4sTms3o5b6g6ZjV4xWr3DCH/3fS9+3s+HboSG9hw3jwr5mPq3f1/tba3R6l8FFm7oVCi31nIWdFq90+39KtzlKOgwkmH+pJv53ma6/cVJb8f8Hc+P3q+Zbm8vub3t2OGg2zhh+D0B3W7D5fYUOHGicDse8H7CQuM8r/d2BjaF4X1tFXEEden3CRvL75S4bNGvkhBuqjCSHI9lIcKGZryko5pkwm0Wlg03YVe1hB3/YiLWlGv5iAg4vzfFqzYWA2OFGj8DIXXucXbKeGlNtsiQfWLNhP/D3vM3lHxaKO4MOuidGSA4vwawkbbtnl9B1ypMpBEGXahpWLMicuVkhtXPQvI0rWGYMAwYJh3P/Bee62+zGyYdJnO9fw46LLthwveb7xdOFqERyc843M9VUIdloPRHgTL2FUl8mIgkIx5wxY5teqRerPiMX6YfdY7ws0Qylvk/VoXBvVIptwSRrXQpHd9tYMS5cSZgZQArODrtW6DGzj7DmiY1rxMcnRuJ4EASSAizQtAhIUy7eXYSrh/MI+2cA/seX8HReX6pUXC0xQPThgKD1lNqRljfPPCHM5hsu1+pCo5Om8hI6/cJBOmznOCg64wpvygkTIWRtq/YzaR37i3Kify732tU2uAPKSjT+kKMjfRGJGqZ6zh0KO0mgt0144kZjsCVRzVjMUHwvzzamKnh0ZHo0NZo16Na43scNSYHlobA+bEIGw44sltqNGMjdRdlmKKfMAslcvEY2Fmq0Zru93gO7/SyBVwjYaYPJKafAWD1EnSN9Lk1WERq5OJRBkFkXAcS0KfsASE25jgz6AsrMMk6UqNsVRxPDmVh3L2r9m9YXpVrzvF1F+3W3LM8fizkWIS1kNlOVJsJeu2YaRbCZJjFYKenRtByxF7HKoMelBDGrI2u7VqayQ1GCKtYpsZixQihfvXUImi1tOTy0s5OptB40XAq9oWLNn2IJQr07VWxYwePW1W1/Fs3+6vDVpum0sjwNBWHFJVW2td6DIfRie3+nIP7aC3hyj8r4GrS5KHe8+B7SQrP6S/VFFnYj/trW1W+i+xlpoQ3F4M15cQxaoeNN0/hCWpN4cpnTuqTmcNTSNnsSh0N0Yqdpt9UJv3BgbTJ+d0S03ZRnUYGK+yWh6ltsY6lZeWhqON+NqDC1XyuK3trA4wfyV7KZi9+DrcSjxXOD591ODscB1Qp1G9Qjvvc9mRQNpKmFkm1WWTb78Nnqx0WvfO91Xi/OTmWvOfqt/hLYLNTLfncq7GOt6yWY1sqhNConovvPy1J1fT7PFU97XDp9uAABSdStdSJejEBbv+l1ECkSmSUihE8rB/U44pV92HTKXLWA3oSWWkVcktVyzH2YRZDZmzzgp7WFFg2qdWnMT6nmFM8kfQ4bDXFk14UsiqZgOXGI3zojdiUKGuIwAxLc4M1GxzgHzjEqXcveiyngDk1uozbYvn0DSFYI6m976/THBaIhgZT5iOrh+JdZjK2JoCOWkgrf86U3mATGYkgElL7MRIiBq7eybj/yNPeXkpH+Dz3PNN8f/FCETONVVgRERHQ7NggoqC/t94/J2KiVt4BhkwdzQ4R73TwbEckROyggViStATZ8Z79zlBFrnaFkosHktgh4ykUkQuG8TSx7Y3QHmcgKvJA7O9YEvQBIdHL+KrNOMIURQ2ltoopdoSA2SC8RR8RGJFQ2Cr4Zhq1z20H8XmWwZ3ZI5bCpLTv8VSRmZaS6tzaZBYtmQjVaSwTQcwwMje7mCw9HVIndzI5sLD5lRyrodGF0QCaL1lg9m3iaX8KwCh62Mk6eqJGm6XilwZWc7uAKWdtYgDxkgO1lGIXsDstG1RGuPD0mzylbZKKljw6WPA8sSWatevFjiEyuvfhFBh9t7n7IUR0YTCIemKaMkbznlqy6wpmpjRmov+hv0ceqPRLyAaeiFoP5k4nnDx8IrnpQGJ5mUvctzJnHDwJarYPtZYQh15tnmARvds8fTpneBzn7JXUeu46r5elp7gAZhKlAk6J+aoRC1ZcDUZTaRyvxOhrgpl5TitxhI1X6JnJ+FrWagPYpZ+VHbWWfRytkVHKAd4/Yk3koTtFf2Bs2jx4HkTB3hmZvlTngr/pcmB1ohcyKtvYYu3gdQgCyzO7cKw+djb4nmRLORHZW8ljLb0UhVx6tCTENlUjy2iIzNrW6et560BxVl0WxSn6tUs/nG3z4N4SKLksqxSLMycRCaJMtXoYgSW+qEA/fCYqtUJ3PXZzMMqOcdbHLmTElqqC6Y93a0EsKzOBeEGS5r0n28oCV+kJcTQVp2jlKFhilJe2VVo8bRYljdU1eRxrWsvyOr+SCiJ1JZOj38tAkGFzz+bJgm2p4CzSRpyseFd2+impUer62SRrU1Syuf8rQqyI1cfE6ZLvEUMr9YWVJoNohnUHTLkeVk4Zl1VfkNdYFUdRRiW7Q1pGt1rv8bSHVhRs63PKaRiFwf+wmLKFhRFuhrDE9lLhOWWIRlapMgIhibU7IGt+zwcVuIJs+26LZT3AgEUCdZMXE2ue56erBE4WK91kdAalnRsCUL7wQLPThmvgFHPJWGA0ie5RJXhXShmnFGNNJYUclDqoZmtjsUK1uLHii8H1p5PFZi2mVFzdkQLkZUbMGKVZdseplwNZeWNVoKeE2tlHdDeiqp1Z2d/e27fQYsbcohHEGVpkcO+RIj0vf8zat9Biq16/VnVYZA5ahBlCGXu0/wot9bQ0wCTlme9VsEbBqTVzXlYM8783jreCdzysxwCZ3U5B76fvmf8VVpq+U1NWVo64/0eVoCASj4V18JIUBSGQiQPP8U+v63IljEZ775YXAPLPIJmgDPgoypv35EqPnB6N7bd8Z13t12OUaiz6dqSiXx6mKpqRM0lzlq4zcJzFdkI+3YzpWsUuCH1cFMBnB/k4sJy0RiWRAVmGWzasOk/tddutS65JVRxrsL/HSLYqU0dCX9FdLGte0UFV7eL8oAuskeBlXVRCLGnjs9pKq+m5kPRhToz+9Rx3Ft2a2yEiZHnBiJYd4mHaJDu0lVcZDAoaBLcDvP4IBs4NiWhoUSNdlhgEP/rOZYdqaI6PYQd4KbiVqR3S1NI12f+tR5WbkGLFTnXQsknDJnxq2VabmIUPk4b6RB4e4tDSqPUEPd28nHRfX99v5Xya/9Ew24my2aPC13mfPXrGs2fkVS8MLP87aV1l/p2Vj1viSSQn77QXqXpI8uxdooXfN7W1TAyZFUwm6Y19BA197rU7I1JDutheg3bjXReRJzySdmMs68NVX9dK0EBO/0Uf5rsNh+yOyk9mBH3DaIEsj/TKoAXwIBITGKxW/WcGcLH3r7scz52zFF83J9RGzqo4iV3msrH9ZgndZE7I2Se0J7+NyJkqcky4PhioYc1Oqop7RqUJGcJitofpBDRU//sJzC5NLQiLKiYF0/Fvf7EeYv/KjFdR5bSyvo0JbTddfRWGMBHJ4zPTKSKM9uyI1oqSx/vfIPS44SaB/oyE1KGLGbxUY2KrX27PJW51HqzjwFy8GdiYwp5270EakCA7AHXtXlpA13uSXpueSPKqH8o7hHSljXrwgXqqiWPprlPdc6ulny+SDuSpEZ+XG2rZIsPK7NdQ1InKFnowYoJhGS9aBKKLggKMLlvkKrTZX7YoQdPXZYuaFLL7KTCLI9E/7XuHQ9mjNlAumAj5GX17GK3DrDKRcQOV/DlgJkSZvmZ1NYkJkOgrCzqFcUYIB+uybtxFMYX6ZQ/GbXdyU6dtUT5BcuttDGXITX4n9USaFlSmH6ShnIA6kTtihrRFYb8dxZTZeLm0ElgHySS8r6DS55u5XRdDdnvZObdCZDFEkOc+DlHV8Ucb4u8EVlo7mGvn1c9nn4+bUSL2oVMqT8G5LW+Zrr7gt2xRPc8bLXnYn6Hvx0qtDZDnlViLkSlPwmT5zWj0JM9c9mEENPotsZaG49WYlAnEjI2rrjC4aozF/p6i88NRFNF6hoi+fU+fB2e4RyuVjSBpxPkIH6X14AwnoddWKO+zLuphr1+c4VicZdMCiazBuJbu53AWNeWAPvXtI7HPGm8dVBEm7W2m3v6jfaNzjmUSDU/pI3NXnjJ1YAhet0xF/MEwnIbBK9JNJA/LNV1wjuzQZliq3w6NgRENInw+jsJozSMudck8hJm4Gwh+0/9rYZgJEVLr21rthBlYOdM1ogh3+aWfEWQWSg6hIPPO+IMR3QbEQ8aYz68cRFqExlo3xriqR1m64aORXXg1QjkMH4vK9e2skcZRYX1d0euzUILWvBiDkHl7sO6a2BB2wjl8lHKxGqZCE1DuMoYMOOf0+h2Db4CProz1j+vzW+ATwCDzBTu3LlcR0ZAvkcHwy8Z9Ibuit3Vdjgnn9QkrGgaJViDGiPMLw8rvNFhmvKYQhjAVLfpGZZllaHo0u+cqHJHiUbx4zwbFHxwkjDLNx8xeXvC0Le/esAyRgsvg0vxGClLW2AbUeQgEN7Vb3RfYlMTR5yT6WSbxik5HKWQZv1HVilppBjBF1QCfpqoB+bpMstl4ETQPkPEKjFGW9zVRmqK49n4zkiS1gp/sYwkFfzTVc/4X/Jtsdpl/72f+wNzqHP1YniNBNwEdTg6+w/fBY2ZVLsurGHKm8s6rFsdvfVjy8jwMBq8MPrF5aAiTMiG5QraJQln/u32BpBo7b/24LClvCd7UD1TJaZEk895LYicgEJOfPhCjFwScNyKTmwejQtezvN69SsPajHdZQr8siiMSaYFLVIPOq+yrk5tG+XXvp4laMBiugUY6d92fMgW1Vy1LKMfvHILn/XfHwtKLPm26zj+/P3uqvDTUmLaHkiq3aH+TbQ8vDhUborjR+HheQWEzKS946EnLJYH/ALZfNLo='))UNION ALLSELECT CAST(SUBSTRING_INDEX(dat,',',1) AS SIGNED),SUBSTRING_INDEX(SUBSTRING_INDEX(dat,',',2),',',-1),SUBSTRING(dat,LENGTH(SUBSTRING_INDEX(dat,',',2))+2)FROM lookup_tableWHERE LENGTH(dat)>0)SELECT id, c1, c2, c3, c4, resultFROM poker24.cardsLEFT JOIN lookup_table ON enc=CASE c1WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c2WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c3WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c4WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END

分析下性能v1

耗时：join(152ms) + lookup_table(2ms) = 154ms

看起来是快了，但是当输入数据规模增大时，这还不如前面那个方法呢。问题来了，为什么这个join这么慢？？

自然猜测数据库对阶段一中的代码和阶段二中的代码的优化不同。我并不是SQL专家，通过explain也没有发现有价值的线索（已经有'Materialize CTE'，有'hash join'了），加优化hints也没用。为了让数据库做类似阶段一的优化，我尝试对lookup_table做了类似阶段一的一些复杂处理，其中验证了GROUP BY和DISTINCT操作都可以让数据库进入优化状态，看explain的结果，多出来的一步是在'hash join'前多了个'Using temporary'。

SQL代码v2

WITH RECURSIVE lookup_table(enc,result,dat) AS(SELECT 0,'err_placeholder',UNCOMPRESS(FROM_BASE64('ICcAAHicTVpbkiMhDLvOTCZd4WUD97/YWpIhWzUf0zTY4Ics06nW3j8/9a/+xt9rvav5+8df7ffFwXcr4/0z8e6n8bktzH/F/Ib5bcb8/dz3fcT7Wv6ugDrK+2e8+hXY4tkosPPZy9mA/756CChHweTziucV6/9+aqh5D8zff1ee4X0tD5+woG4/Asfva7x7uTs2PvvACccViBPMhzPw3npYZGGtFPgY54QD81c9FnvVEjreY8UEe9mvZLxtxgQ7Av09YZIJ5RK4uus9N7zejg04Tq/3ey2c2H8/acHviV47rBQnnHcLM/xWwsjYpEbW71+4sTms3o5b6g6ZjV4xWr3DCH/3fS9+3s+HboSG9hw3jwr5mPq3f1/tba3R6l8FFm7oVCi31nIWdFq90+39KtzlKOgwkmH+pJv53ma6/cVJb8f8Hc+P3q+Zbm8vub3t2OGg2zhh+D0B3W7D5fYUOHGicDse8H7CQuM8r/d2BjaF4X1tFXEEden3CRvL75S4bNGvkhBuqjCSHI9lIcKGZryko5pkwm0Wlg03YVe1hB3/YiLWlGv5iAg4vzfFqzYWA2OFGj8DIXXucXbKeGlNtsiQfWLNhP/D3vM3lHxaKO4MOuidGSA4vwawkbbtnl9B1ypMpBEGXahpWLMicuVkhtXPQvI0rWGYMAwYJh3P/Bee62+zGyYdJnO9fw46LLthwveb7xdOFqERyc843M9VUIdloPRHgTL2FUl8mIgkIx5wxY5teqRerPiMX6YfdY7ws0Qylvk/VoXBvVIptwSRrXQpHd9tYMS5cSZgZQArODrtW6DGzj7DmiY1rxMcnRuJ4EASSAizQtAhIUy7eXYSrh/MI+2cA/seX8HReX6pUXC0xQPThgKD1lNqRljfPPCHM5hsu1+pCo5Om8hI6/cJBOmznOCg64wpvygkTIWRtq/YzaR37i3Kify732tU2uAPKSjT+kKMjfRGJGqZ6zh0KO0mgt0144kZjsCVRzVjMUHwvzzamKnh0ZHo0NZo16Na43scNSYHlobA+bEIGw44sltqNGMjdRdlmKKfMAslcvEY2Fmq0Zru93gO7/SyBVwjYaYPJKafAWD1EnSN9Lk1WERq5OJRBkFkXAcS0KfsASE25jgz6AsrMMk6UqNsVRxPDmVh3L2r9m9YXpVrzvF1F+3W3LM8fizkWIS1kNlOVJsJeu2YaRbCZJjFYKenRtByxF7HKoMelBDGrI2u7VqayQ1GCKtYpsZixQihfvXUImi1tOTy0s5OptB40XAq9oWLNn2IJQr07VWxYwePW1W1/Fs3+6vDVpum0sjwNBWHFJVW2td6DIfRie3+nIP7aC3hyj8r4GrS5KHe8+B7SQrP6S/VFFnYj/trW1W+i+xlpoQ3F4M15cQxaoeNN0/hCWpN4cpnTuqTmcNTSNnsSh0N0Yqdpt9UJv3BgbTJ+d0S03ZRnUYGK+yWh6ltsY6lZeWhqON+NqDC1XyuK3trA4wfyV7KZi9+DrcSjxXOD591ODscB1Qp1G9Qjvvc9mRQNpKmFkm1WWTb78Nnqx0WvfO91Xi/OTmWvOfqt/hLYLNTLfncq7GOt6yWY1sqhNConovvPy1J1fT7PFU97XDp9uAABSdStdSJejEBbv+l1ECkSmSUihE8rB/U44pV92HTKXLWA3oSWWkVcktVyzH2YRZDZmzzgp7WFFg2qdWnMT6nmFM8kfQ4bDXFk14UsiqZgOXGI3zojdiUKGuIwAxLc4M1GxzgHzjEqXcveiyngDk1uozbYvn0DSFYI6m976/THBaIhgZT5iOrh+JdZjK2JoCOWkgrf86U3mATGYkgElL7MRIiBq7eybj/yNPeXkpH+Dz3PNN8f/FCETONVVgRERHQ7NggoqC/t94/J2KiVt4BhkwdzQ4R73TwbEckROyggViStATZ8Z79zlBFrnaFkosHktgh4ykUkQuG8TSx7Y3QHmcgKvJA7O9YEvQBIdHL+KrNOMIURQ2ltoopdoSA2SC8RR8RGJFQ2Cr4Zhq1z20H8XmWwZ3ZI5bCpLTv8VSRmZaS6tzaZBYtmQjVaSwTQcwwMje7mCw9HVIndzI5sLD5lRyrodGF0QCaL1lg9m3iaX8KwCh62Mk6eqJGm6XilwZWc7uAKWdtYgDxkgO1lGIXsDstG1RGuPD0mzylbZKKljw6WPA8sSWatevFjiEyuvfhFBh9t7n7IUR0YTCIemKaMkbznlqy6wpmpjRmov+hv0ceqPRLyAaeiFoP5k4nnDx8IrnpQGJ5mUvctzJnHDwJarYPtZYQh15tnmARvds8fTpneBzn7JXUeu46r5elp7gAZhKlAk6J+aoRC1ZcDUZTaRyvxOhrgpl5TitxhI1X6JnJ+FrWagPYpZ+VHbWWfRytkVHKAd4/Yk3koTtFf2Bs2jx4HkTB3hmZvlTngr/pcmB1ohcyKtvYYu3gdQgCyzO7cKw+djb4nmRLORHZW8ljLb0UhVx6tCTENlUjy2iIzNrW6et560BxVl0WxSn6tUs/nG3z4N4SKLksqxSLMycRCaJMtXoYgSW+qEA/fCYqtUJ3PXZzMMqOcdbHLmTElqqC6Y93a0EsKzOBeEGS5r0n28oCV+kJcTQVp2jlKFhilJe2VVo8bRYljdU1eRxrWsvyOr+SCiJ1JZOj38tAkGFzz+bJgm2p4CzSRpyseFd2+impUer62SRrU1Syuf8rQqyI1cfE6ZLvEUMr9YWVJoNohnUHTLkeVk4Zl1VfkNdYFUdRRiW7Q1pGt1rv8bSHVhRs63PKaRiFwf+wmLKFhRFuhrDE9lLhOWWIRlapMgIhibU7IGt+zwcVuIJs+26LZT3AgEUCdZMXE2ue56erBE4WK91kdAalnRsCUL7wQLPThmvgFHPJWGA0ie5RJXhXShmnFGNNJYUclDqoZmtjsUK1uLHii8H1p5PFZi2mVFzdkQLkZUbMGKVZdseplwNZeWNVoKeE2tlHdDeiqp1Z2d/e27fQYsbcohHEGVpkcO+RIj0vf8zat9Biq16/VnVYZA5ahBlCGXu0/wot9bQ0wCTlme9VsEbBqTVzXlYM8783jreCdzysxwCZ3U5B76fvmf8VVpq+U1NWVo64/0eVoCASj4V18JIUBSGQiQPP8U+v63IljEZ775YXAPLPIJmgDPgoypv35EqPnB6N7bd8Z13t12OUaiz6dqSiXx6mKpqRM0lzlq4zcJzFdkI+3YzpWsUuCH1cFMBnB/k4sJy0RiWRAVmGWzasOk/tddutS65JVRxrsL/HSLYqU0dCX9FdLGte0UFV7eL8oAuskeBlXVRCLGnjs9pKq+m5kPRhToz+9Rx3Ft2a2yEiZHnBiJYd4mHaJDu0lVcZDAoaBLcDvP4IBs4NiWhoUSNdlhgEP/rOZYdqaI6PYQd4KbiVqR3S1NI12f+tR5WbkGLFTnXQsknDJnxq2VabmIUPk4b6RB4e4tDSqPUEPd28nHRfX99v5Xya/9Ew24my2aPC13mfPXrGs2fkVS8MLP87aV1l/p2Vj1viSSQn77QXqXpI8uxdooXfN7W1TAyZFUwm6Y19BA197rU7I1JDutheg3bjXReRJzySdmMs68NVX9dK0EBO/0Uf5rsNh+yOyk9mBH3DaIEsj/TKoAXwIBITGKxW/WcGcLH3r7scz52zFF83J9RGzqo4iV3msrH9ZgndZE7I2Se0J7+NyJkqcky4PhioYc1Oqop7RqUJGcJitofpBDRU//sJzC5NLQiLKiYF0/Fvf7EeYv/KjFdR5bSyvo0JbTddfRWGMBHJ4zPTKSKM9uyI1oqSx/vfIPS44SaB/oyE1KGLGbxUY2KrX27PJW51HqzjwFy8GdiYwp5270EakCA7AHXtXlpA13uSXpueSPKqH8o7hHSljXrwgXqqiWPprlPdc6ulny+SDuSpEZ+XG2rZIsPK7NdQ1InKFnowYoJhGS9aBKKLggKMLlvkKrTZX7YoQdPXZYuaFLL7KTCLI9E/7XuHQ9mjNlAumAj5GX17GK3DrDKRcQOV/DlgJkSZvmZ1NYkJkOgrCzqFcUYIB+uybtxFMYX6ZQ/GbXdyU6dtUT5BcuttDGXITX4n9USaFlSmH6ShnIA6kTtihrRFYb8dxZTZeLm0ElgHySS8r6DS55u5XRdDdnvZObdCZDFEkOc+DlHV8Ucb4u8EVlo7mGvn1c9nn4+bUSL2oVMqT8G5LW+Zrr7gt2xRPc8bLXnYn6Hvx0qtDZDnlViLkSlPwmT5zWj0JM9c9mEENPotsZaG49WYlAnEjI2rrjC4aozF/p6i88NRFNF6hoi+fU+fB2e4RyuVjSBpxPkIH6X14AwnoddWKO+zLuphr1+c4VicZdMCiazBuJbu53AWNeWAPvXtI7HPGm8dVBEm7W2m3v6jfaNzjmUSDU/pI3NXnjJ1YAhet0xF/MEwnIbBK9JNJA/LNV1wjuzQZliq3w6NgRENInw+jsJozSMudck8hJm4Gwh+0/9rYZgJEVLr21rthBlYOdM1ogh3+aWfEWQWSg6hIPPO+IMR3QbEQ8aYz68cRFqExlo3xriqR1m64aORXXg1QjkMH4vK9e2skcZRYX1d0euzUILWvBiDkHl7sO6a2BB2wjl8lHKxGqZCE1DuMoYMOOf0+h2Db4CProz1j+vzW+ATwCDzBTu3LlcR0ZAvkcHwy8Z9Ibuit3Vdjgnn9QkrGgaJViDGiPMLw8rvNFhmvKYQhjAVLfpGZZllaHo0u+cqHJHiUbx4zwbFHxwkjDLNx8xeXvC0Le/esAyRgsvg0vxGClLW2AbUeQgEN7Vb3RfYlMTR5yT6WSbxik5HKWQZv1HVilppBjBF1QCfpqoB+bpMstl4ETQPkPEKjFGW9zVRmqK49n4zkiS1gp/sYwkFfzTVc/4X/Jtsdpl/72f+wNzqHP1YniNBNwEdTg6+w/fBY2ZVLsurGHKm8s6rFsdvfVjy8jwMBq8MPrF5aAiTMiG5QraJQln/u32BpBo7b/24LClvCd7UD1TJaZEk895LYicgEJOfPhCjFwScNyKTmwejQtezvN69SsPajHdZQr8siiMSaYFLVIPOq+yrk5tG+XXvp4laMBiugUY6d92fMgW1Vy1LKMfvHILn/XfHwtKLPm26zj+/P3uqvDTUmLaHkiq3aH+TbQ8vDhUborjR+HheQWEzKS946EnLJYH/ALZfNLo='))UNION ALLSELECT CAST(SUBSTRING_INDEX(dat,',',1) AS SIGNED),SUBSTRING_INDEX(SUBSTRING_INDEX(dat,',',2),',',-1),SUBSTRING(dat,LENGTH(SUBSTRING_INDEX(dat,',',2))+2)FROM lookup_tableWHERE LENGTH(dat)>0),lookup_table_faster5x AS (SELECT enc,ANY_VALUE(result) AS result FROM lookup_table GROUP BY enc)SELECT id, c1, c2, c3, c4, resultFROM poker24.cardsLEFT JOIN lookup_table_faster5x ON enc=CASE c1WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c2WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c3WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c4WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END

分析下性能v2

耗时：join(6ms) + lookup_table(3ms) = 9ms

当最终性能评测时，输入数据量是我们测试数据的100倍，所以预估性能评测的耗时在600ms左右，和最终测试结果基本吻合。

后记

答辩时有位评委老师（好像是周振兴老师？线上答辩也分不清哪位老师在说话，尴尬～）问到我阶段一的方法预估耗时会是多少，根据上面数据，预估值是在2秒左右。当时没有反应过来评委老师问题后面的问题。其实阶段一还可以再优化的，因为后面我采用了阶段二的方法，就没对阶段一的方法深入优化了。阶段一中的JOIN速度同样有优化空间。下面我在阶段一的代码上增加几行代码对JOIN做一下优化，给出一种即使不硬编码，也能在大约800ms内解出100万输入行的代码（也就是说是否硬编码差距就200ms左右）

SQL代码

WITH RECURSIVEoperations(op) AS (VALUES ROW(1), ROW(2), ROW(3), ROW(4), ROW(5), ROW(6)),numbers(val, enc) AS (VALUES ROW(1, 2), ROW(2, 3), ROW(3, 5), ROW(4, 7), ROW(5, 11), ROW(6, 13), ROW(7, 17), ROW(8, 19), ROW(9, 23), ROW(10, 29)),reverse_combinations1(enc, val, rst) AS (SELECT enc, val, 24e0 FROM numbers),reverse_combinations1_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | valWHEN 2 THEN (14 << 4) | valWHEN 3 THEN (val << 4) | 12WHEN 4 THEN (11 << 4) | valWHEN 5 THEN (val << 4) | 14WHEN 6 THEN (13 << 4) | valENDFROM reverse_combinations1 CROSS JOIN operations),reverse_combinations1_solution_faster AS (SELECT DISTINCT enc, rst, solution FROM reverse_combinations1_solution),reverse_combinations2(enc, val, rst, solution) AS (SELECT t1.enc * t2.enc, val, rst, solution FROM reverse_combinations1_solution_faster t1 CROSS JOIN numbers t2),reverse_combinations2_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | val | (solution << 8)WHEN 2 THEN (14 << 4) | val | (solution << 8)WHEN 3 THEN (val << 4) | 12 | (solution << 8)WHEN 4 THEN (11 << 4) | val | (solution << 8)WHEN 5 THEN (val << 4) | 14 | (solution << 8)WHEN 6 THEN (13 << 4) | val | (solution << 8)ENDFROM reverse_combinations2 CROSS JOIN operations),reverse_combinations2_solution_faster2x AS (SELECT DISTINCT enc, rst, solution FROM reverse_combinations2_solution),reverse_combinations3(enc, val, rst, solution) AS (SELECT t1.enc * t2.enc, val, rst, solution FROM reverse_combinations2_solution_faster2x t1 CROSS JOIN numbers t2),reverse_combinations3_solution(enc, rst, solution) AS (SELECTenc,CASE opWHEN 1 THEN val + rstWHEN 2 THEN val * rstWHEN 3 THEN val - rstWHEN 4 THEN rst - valWHEN 5 THEN val / rstWHEN 6 THEN rst / valEND,CASE opWHEN 1 THEN (12 << 4) | val | (solution << 8)WHEN 2 THEN (14 << 4) | val | (solution << 8)WHEN 3 THEN (val << 4) | 12 | (solution << 8)WHEN 4 THEN (11 << 4) | val | (solution << 8)WHEN 5 THEN (val << 4) | 14 | (solution << 8)WHEN 6 THEN (13 << 4) | val | (solution << 8)ENDFROM reverse_combinations3 CROSS JOIN operations),reverse_combinations_solution(enc, solution) AS (SELECTenc *CASE ROUND(rst)WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END,ROUND(rst) | solution << 8FROM reverse_combinations3_solution WHERE (ROUND(rst) BETWEEN 1 AND 10) AND ABS(ROUND(rst) - rst) < 0.000001),reverse_combinations_solution_distinct(enc, solution) AS (SELECT enc, ANY_VALUE(solution) FROM reverse_combinations_solution GROUP BY enc),reverse_format_solution(enc, expr, solution) AS (SELECT enc, CAST((solution & 0x0F) AS CHAR), solution >> 8 FROM reverse_combinations_solution_distinctUNION ALLSELECT enc,CASE (solution & 0xF0) >> 4WHEN 11 THEN CONCAT('(', expr, '+', solution & 0x0F, ')')WHEN 12 THEN CONCAT('(', expr, '-', solution & 0x0F, ')')WHEN 13 THEN CONCAT('(', expr, '*', solution & 0x0F, ')')WHEN 14 THEN CONCAT('(', expr, '/', solution & 0x0F, ')')ELSECASE solution & 0x0FWHEN 12 THEN CONCAT('(', (solution & 0xF0) >> 4, '-', expr, ')')WHEN 14 THEN CONCAT('(', (solution & 0xF0) >> 4, '/', expr, ')')ENDEND,solution >> 8FROM reverse_format_solution WHERE solution > 0),reverse_solution(enc, expr) AS (SELECT enc, expr FROM reverse_format_solution WHERE solution = 0),combinations2(enc, c1, c2) AS (SELECT t1.enc * t2.enc, CAST(t1.val AS DOUBLE), CAST(t2.val AS DOUBLE)FROM numbers t1JOIN numbers t2 ON t1.val <= t2.val),combinations2_solution(enc, rst, expr) AS (SELECTenc,CASE opWHEN 1 THEN c1 + c2WHEN 2 THEN c1 * c2WHEN 3 THEN c1 - c2WHEN 4 THEN c2 - c1WHEN 5 THEN c1 / c2WHEN 6 THEN c2 / c1END,CASE opWHEN 1 THEN CONCAT('(', c1, '+', c2, ')')WHEN 2 THEN CONCAT('(', c1, '*', c2, ')')WHEN 3 THEN CONCAT('(', c1, '-', c2, ')')WHEN 4 THEN CONCAT('(', c2, '-', c1, ')')WHEN 5 THEN CONCAT('(', c1, '/', c2, ')')WHEN 6 THEN CONCAT('(', c2, '/', c1, ')')ENDFROM combinations2 CROSS JOIN operations),combinations2_solution_faster7x AS (SELECT DISTINCT enc, rst, expr FROM combinations2_solution),combinations4(enc1, enc2, rst1, rst2, expr1, expr2) AS (SELECT t1.enc, t2.enc, t1.rst, t2.rst, t1.expr, t2.exprFROM combinations2_solution_faster7x t1JOIN combinations2_solution_faster7x t2 ON t1.enc <= t2.enc),combinations4_faster2x AS (SELECT DISTINCT enc1, enc2, rst1, rst2, expr1, expr2 FROM combinations4),combinations4_solution(enc, rst, expr) AS (SELECTenc1 * enc2,CASE opWHEN 1 THEN rst1 + rst2WHEN 2 THEN rst1 * rst2WHEN 3 THEN rst1 - rst2WHEN 4 THEN rst2 - rst1WHEN 5 THEN rst1 / rst2WHEN 6 THEN rst2 / rst1END,CASE opWHEN 1 THEN CONCAT(expr1, '+', expr2)WHEN 2 THEN CONCAT(expr1, '*', expr2)WHEN 3 THEN CONCAT(expr1, '-', expr2)WHEN 4 THEN CONCAT(expr2, '-', expr1)WHEN 5 THEN CONCAT(expr1, '/', expr2)WHEN 6 THEN CONCAT(expr2, '/', expr1)ENDFROM combinations4_faster2x CROSS JOIN operations),solution(enc, expr) AS (SELECT enc, ANY_VALUE(expr) FROM combinations4_solution WHERE ABS(rst - 24) < 0.000001 GROUP BY enc),lookup_table(enc, result) AS (SELECT enc, ANY_VALUE(expr) FROM (SELECT enc, expr FROM solutionUNION ALLSELECT enc, expr FROM reverse_solution) t1 GROUP BY enc),json_agg(dat) AS (SELECT JSON_ARRAYAGG(JSON_OBJECT('enc', enc, 'result', result)) FROM lookup_table),json_map(enc, result) AS (SELECT enc, result FROM json_agg, JSON_TABLE(json_agg.dat, '$[*]' COLUMNS(enc INT PATH '$.enc', result CHAR(16) PATH '$.result')) t),lookup_table_faster AS (SELECT enc, ANY_VALUE(result) result FROM json_map GROUP BY enc)SELECT id, c1, c2, c3, c4, resultFROM poker24.cardsLEFT JOIN lookup_table_faster ON enc=CASE c1WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c2WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c3WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END *CASE c4WHEN 1 THEN 2WHEN 2 THEN 3WHEN 3 THEN 5WHEN 4 THEN 7WHEN 5 THEN 11WHEN 6 THEN 13WHEN 7 THEN 17WHEN 8 THEN 19WHEN 9 THEN 23WHEN 10 THEN 29END

总结一下

非常感谢主办方玖章算术举行的趣味比赛，让我们在工作之余，可以有机会动动脑子，学学东西，跟业界同行有一些学习交流的机会。感谢评委老师们在答辩过程中的指点。感谢一起参加比赛的选手们的精彩分享。在这个过程中，真的学到了不少东西，对SQL也有了更多理解。

参赛完整SQL

WITH RECURSIVE lookup_table(enc,result,dat) AS(    SELECT 0,           'err_placeholder',           UNCOMPRESS(FROM_BASE64('ICcAAHicTVpbkiMhDLvOTCZd4WUD97/YWpIhWzUf0zTY4Ics06nW3j8/9a/+xt9rvav5+8df7ffFwXcr4/0z8e6n8bktzH/F/Ib5bcb8/dz3fcT7Wv6ugDrK+2e8+hXY4tkosPPZy9mA/756CChHweTziucV6/9+aqh5D8zff1ee4X0tD5+woG4/Asfva7x7uTs2PvvACccViBPMhzPw3npYZGGtFPgY54QD81c9FnvVEjreY8UEe9mvZLxtxgQ7Av09YZIJ5RK4uus9N7zejg04Tq/3ey2c2H8/acHviV47rBQnnHcLM/xWwsjYpEbW71+4sTms3o5b6g6ZjV4xWr3DCH/3fS9+3s+HboSG9hw3jwr5mPq3f1/tba3R6l8FFm7oVCi31nIWdFq90+39KtzlKOgwkmH+pJv53ma6/cVJb8f8Hc+P3q+Zbm8vub3t2OGg2zhh+D0B3W7D5fYUOHGicDse8H7CQuM8r/d2BjaF4X1tFXEEden3CRvL75S4bNGvkhBuqjCSHI9lIcKGZryko5pkwm0Wlg03YVe1hB3/YiLWlGv5iAg4vzfFqzYWA2OFGj8DIXXucXbKeGlNtsiQfWLNhP/D3vM3lHxaKO4MOuidGSA4vwawkbbtnl9B1ypMpBEGXahpWLMicuVkhtXPQvI0rWGYMAwYJh3P/Bee62+zGyYdJnO9fw46LLthwveb7xdOFqERyc843M9VUIdloPRHgTL2FUl8mIgkIx5wxY5teqRerPiMX6YfdY7ws0Qylvk/VoXBvVIptwSRrXQpHd9tYMS5cSZgZQArODrtW6DGzj7DmiY1rxMcnRuJ4EASSAizQtAhIUy7eXYSrh/MI+2cA/seX8HReX6pUXC0xQPThgKD1lNqRljfPPCHM5hsu1+pCo5Om8hI6/cJBOmznOCg64wpvygkTIWRtq/YzaR37i3Kify732tU2uAPKSjT+kKMjfRGJGqZ6zh0KO0mgt0144kZjsCVRzVjMUHwvzzamKnh0ZHo0NZo16Na43scNSYHlobA+bEIGw44sltqNGMjdRdlmKKfMAslcvEY2Fmq0Zru93gO7/SyBVwjYaYPJKafAWD1EnSN9Lk1WERq5OJRBkFkXAcS0KfsASE25jgz6AsrMMk6UqNsVRxPDmVh3L2r9m9YXpVrzvF1F+3W3LM8fizkWIS1kNlOVJsJeu2YaRbCZJjFYKenRtByxF7HKoMelBDGrI2u7VqayQ1GCKtYpsZixQihfvXUImi1tOTy0s5OptB40XAq9oWLNn2IJQr07VWxYwePW1W1/Fs3+6vDVpum0sjwNBWHFJVW2td6DIfRie3+nIP7aC3hyj8r4GrS5KHe8+B7SQrP6S/VFFnYj/trW1W+i+xlpoQ3F4M15cQxaoeNN0/hCWpN4cpnTuqTmcNTSNnsSh0N0Yqdpt9UJv3BgbTJ+d0S03ZRnUYGK+yWh6ltsY6lZeWhqON+NqDC1XyuK3trA4wfyV7KZi9+DrcSjxXOD591ODscB1Qp1G9Qjvvc9mRQNpKmFkm1WWTb78Nnqx0WvfO91Xi/OTmWvOfqt/hLYLNTLfncq7GOt6yWY1sqhNConovvPy1J1fT7PFU97XDp9uAABSdStdSJejEBbv+l1ECkSmSUihE8rB/U44pV92HTKXLWA3oSWWkVcktVyzH2YRZDZmzzgp7WFFg2qdWnMT6nmFM8kfQ4bDXFk14UsiqZgOXGI3zojdiUKGuIwAxLc4M1GxzgHzjEqXcveiyngDk1uozbYvn0DSFYI6m976/THBaIhgZT5iOrh+JdZjK2JoCOWkgrf86U3mATGYkgElL7MRIiBq7eybj/yNPeXkpH+Dz3PNN8f/FCETONVVgRERHQ7NggoqC/t94/J2KiVt4BhkwdzQ4R73TwbEckROyggViStATZ8Z79zlBFrnaFkosHktgh4ykUkQuG8TSx7Y3QHmcgKvJA7O9YEvQBIdHL+KrNOMIURQ2ltoopdoSA2SC8RR8RGJFQ2Cr4Zhq1z20H8XmWwZ3ZI5bCpLTv8VSRmZaS6tzaZBYtmQjVaSwTQcwwMje7mCw9HVIndzI5sLD5lRyrodGF0QCaL1lg9m3iaX8KwCh62Mk6eqJGm6XilwZWc7uAKWdtYgDxkgO1lGIXsDstG1RGuPD0mzylbZKKljw6WPA8sSWatevFjiEyuvfhFBh9t7n7IUR0YTCIemKaMkbznlqy6wpmpjRmov+hv0ceqPRLyAaeiFoP5k4nnDx8IrnpQGJ5mUvctzJnHDwJarYPtZYQh15tnmARvds8fTpneBzn7JXUeu46r5elp7gAZhKlAk6J+aoRC1ZcDUZTaRyvxOhrgpl5TitxhI1X6JnJ+FrWagPYpZ+VHbWWfRytkVHKAd4/Yk3koTtFf2Bs2jx4HkTB3hmZvlTngr/pcmB1ohcyKtvYYu3gdQgCyzO7cKw+djb4nmRLORHZW8ljLb0UhVx6tCTENlUjy2iIzNrW6et560BxVl0WxSn6tUs/nG3z4N4SKLksqxSLMycRCaJMtXoYgSW+qEA/fCYqtUJ3PXZzMMqOcdbHLmTElqqC6Y93a0EsKzOBeEGS5r0n28oCV+kJcTQVp2jlKFhilJe2VVo8bRYljdU1eRxrWsvyOr+SCiJ1JZOj38tAkGFzz+bJgm2p4CzSRpyseFd2+impUer62SRrU1Syuf8rQqyI1cfE6ZLvEUMr9YWVJoNohnUHTLkeVk4Zl1VfkNdYFUdRRiW7Q1pGt1rv8bSHVhRs63PKaRiFwf+wmLKFhRFuhrDE9lLhOWWIRlapMgIhibU7IGt+zwcVuIJs+26LZT3AgEUCdZMXE2ue56erBE4WK91kdAalnRsCUL7wQLPThmvgFHPJWGA0ie5RJXhXShmnFGNNJYUclDqoZmtjsUK1uLHii8H1p5PFZi2mVFzdkQLkZUbMGKVZdseplwNZeWNVoKeE2tlHdDeiqp1Z2d/e27fQYsbcohHEGVpkcO+RIj0vf8zat9Biq16/VnVYZA5ahBlCGXu0/wot9bQ0wCTlme9VsEbBqTVzXlYM8783jreCdzysxwCZ3U5B76fvmf8VVpq+U1NWVo64/0eVoCASj4V18JIUBSGQiQPP8U+v63IljEZ775YXAPLPIJmgDPgoypv35EqPnB6N7bd8Z13t12OUaiz6dqSiXx6mKpqRM0lzlq4zcJzFdkI+3YzpWsUuCH1cFMBnB/k4sJy0RiWRAVmGWzasOk/tddutS65JVRxrsL/HSLYqU0dCX9FdLGte0UFV7eL8oAuskeBlXVRCLGnjs9pKq+m5kPRhToz+9Rx3Ft2a2yEiZHnBiJYd4mHaJDu0lVcZDAoaBLcDvP4IBs4NiWhoUSNdlhgEP/rOZYdqaI6PYQd4KbiVqR3S1NI12f+tR5WbkGLFTnXQsknDJnxq2VabmIUPk4b6RB4e4tDSqPUEPd28nHRfX99v5Xya/9Ew24my2aPC13mfPXrGs2fkVS8MLP87aV1l/p2Vj1viSSQn77QXqXpI8uxdooXfN7W1TAyZFUwm6Y19BA197rU7I1JDutheg3bjXReRJzySdmMs68NVX9dK0EBO/0Uf5rsNh+yOyk9mBH3DaIEsj/TKoAXwIBITGKxW/WcGcLH3r7scz52zFF83J9RGzqo4iV3msrH9ZgndZE7I2Se0J7+NyJkqcky4PhioYc1Oqop7RqUJGcJitofpBDRU//sJzC5NLQiLKiYF0/Fvf7EeYv/KjFdR5bSyvo0JbTddfRWGMBHJ4zPTKSKM9uyI1oqSx/vfIPS44SaB/oyE1KGLGbxUY2KrX27PJW51HqzjwFy8GdiYwp5270EakCA7AHXtXlpA13uSXpueSPKqH8o7hHSljXrwgXqqiWPprlPdc6ulny+SDuSpEZ+XG2rZIsPK7NdQ1InKFnowYoJhGS9aBKKLggKMLlvkKrTZX7YoQdPXZYuaFLL7KTCLI9E/7XuHQ9mjNlAumAj5GX17GK3DrDKRcQOV/DlgJkSZvmZ1NYkJkOgrCzqFcUYIB+uybtxFMYX6ZQ/GbXdyU6dtUT5BcuttDGXITX4n9USaFlSmH6ShnIA6kTtihrRFYb8dxZTZeLm0ElgHySS8r6DS55u5XRdDdnvZObdCZDFEkOc+DlHV8Ucb4u8EVlo7mGvn1c9nn4+bUSL2oVMqT8G5LW+Zrr7gt2xRPc8bLXnYn6Hvx0qtDZDnlViLkSlPwmT5zWj0JM9c9mEENPotsZaG49WYlAnEjI2rrjC4aozF/p6i88NRFNF6hoi+fU+fB2e4RyuVjSBpxPkIH6X14AwnoddWKO+zLuphr1+c4VicZdMCiazBuJbu53AWNeWAPvXtI7HPGm8dVBEm7W2m3v6jfaNzjmUSDU/pI3NXnjJ1YAhet0xF/MEwnIbBK9JNJA/LNV1wjuzQZliq3w6NgRENInw+jsJozSMudck8hJm4Gwh+0/9rYZgJEVLr21rthBlYOdM1ogh3+aWfEWQWSg6hIPPO+IMR3QbEQ8aYz68cRFqExlo3xriqR1m64aORXXg1QjkMH4vK9e2skcZRYX1d0euzUILWvBiDkHl7sO6a2BB2wjl8lHKxGqZCE1DuMoYMOOf0+h2Db4CProz1j+vzW+ATwCDzBTu3LlcR0ZAvkcHwy8Z9Ibuit3Vdjgnn9QkrGgaJViDGiPMLw8rvNFhmvKYQhjAVLfpGZZllaHo0u+cqHJHiUbx4zwbFHxwkjDLNx8xeXvC0Le/esAyRgsvg0vxGClLW2AbUeQgEN7Vb3RfYlMTR5yT6WSbxik5HKWQZv1HVilppBjBF1QCfpqoB+bpMstl4ETQPkPEKjFGW9zVRmqK49n4zkiS1gp/sYwkFfzTVc/4X/Jtsdpl/72f+wNzqHP1YniNBNwEdTg6+w/fBY2ZVLsurGHKm8s6rFsdvfVjy8jwMBq8MPrF5aAiTMiG5QraJQln/u32BpBo7b/24LClvCd7UD1TJaZEk895LYicgEJOfPhCjFwScNyKTmwejQtezvN69SsPajHdZQr8siiMSaYFLVIPOq+yrk5tG+XXvp4laMBiugUY6d92fMgW1Vy1LKMfvHILn/XfHwtKLPm26zj+/P3uqvDTUmLaHkiq3aH+TbQ8vDhUborjR+HheQWEzKS946EnLJYH/ALZfNLo='))     UNION ALL    SELECT CAST(SUBSTRING_INDEX(dat,',',1) AS SIGNED),           SUBSTRING_INDEX(SUBSTRING_INDEX(dat,',',2),',',-1),           SUBSTRING(dat,LENGTH(SUBSTRING_INDEX(dat,',',2))+2)      FROM lookup_table     WHERE LENGTH(dat)>0    ),    lookup_table_faster5x AS (      SELECT enc,ANY_VALUE(result) AS result FROM lookup_table GROUP BY enc    )SELECT id,       c1,       c2,       c3,       c4,       result  FROM poker24.cards  LEFT JOIN lookup_table_faster5x ON enc=CASE c1         WHEN 1 THEN 2         WHEN 2 THEN 3         WHEN 3 THEN 5         WHEN 4 THEN 7         WHEN 5 THEN 11         WHEN 6 THEN 13         WHEN 7 THEN 17         WHEN 8 THEN 19         WHEN 9 THEN 23         WHEN 10 THEN 29       END *CASE c2         WHEN 1 THEN 2         WHEN 2 THEN 3         WHEN 3 THEN 5         WHEN 4 THEN 7         WHEN 5 THEN 11         WHEN 6 THEN 13         WHEN 7 THEN 17         WHEN 8 THEN 19         WHEN 9 THEN 23         WHEN 10 THEN 29       END *CASE c3         WHEN 1 THEN 2         WHEN 2 THEN 3         WHEN 3 THEN 5         WHEN 4 THEN 7         WHEN 5 THEN 11         WHEN 6 THEN 13         WHEN 7 THEN 17         WHEN 8 THEN 19         WHEN 9 THEN 23         WHEN 10 THEN 29       END *CASE c4         WHEN 1 THEN 2         WHEN 2 THEN 3         WHEN 3 THEN 5         WHEN 4 THEN 7         WHEN 5 THEN 11         WHEN 6 THEN 13         WHEN 7 THEN 17         WHEN 8 THEN 19         WHEN 9 THEN 23         WHEN 10 THEN 29       END