如何从MySQL中的每个类别获取RANDOM记录?

时间:2015-07-18 20:49:03

标签: mysql sql

在我的MySQL数据库中,我有一个表格,其中包含不同类别的不同问题。

我想编写一个返回EACH类别的3个RANDOM问题的SQL语句。

以下是数据库记录的示例:

id  question    category
1   Question A  1
2   Question B  1
3   Question C  1
4   Question D  1
5   Question D  1
6   Question F  2
7   Question G  2
8   Question H  2
9   Question I  2
10  Question J  2
11  Question K  3
12  Question L  3
13  Question M  3
14  Question N  3
15  Question O  3
16  Question P  3

以下是从上面列表中的每个类别的所有问题中选择并随机播放3个随机的输出/结果:

2   Question B  1
4   Question D  1
3   Question C  1
10  Question J  2
7   Question G  2
9   Question I  2
11  Question K  3
15  Question P  3
13  Question M  3

到目前为止,我已使用以下语句进行测试:

SELECT * FROM `random` ORDER BY RAND() LIMIT 0,3;

这只返回所有类别的3个RANDOM问题。

之后我在此链接中查找了示例: MYSQL select random of each of the categories

尝试了这个:

(SELECT * FROM `random` WHERE category = 1 ORDER BY RAND() LIMIT 3)
UNION ALL
(SELECT * FROM `random` WHERE category = 2 ORDER BY RAND() LIMIT 3)
UNION ALL
(SELECT * FROM `random` WHERE category = 3 ORDER BY RAND() LIMIT 3)

但在这里我需要手动添加每个类别。

我的问题:我很奇怪是否可以从所有类别的每个类别(自动)中获取3个RANDOM记录/行?

编辑

这不是问题的一部分,而是帮助。

虚拟数据创建者 查询代码将调用random表并创建一个名为create_random的存储过程,当您运行存储过程时,它将在随机表中创建随机虚拟数据:

DELIMITER $$
DROP TABLE IF EXISTS `random`;
DROP PROCEDURE IF EXISTS `create_random` $$

CREATE TABLE `random` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `question` VARCHAR(50) NULL DEFAULT NULL,
    `category` VARCHAR(50) NULL DEFAULT NULL,
    PRIMARY KEY (`id`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
AUTO_INCREMENT=401
;

CREATE DEFINER=`root`@`localhost`
PROCEDURE `create_random`()
    LANGUAGE SQL
    NOT DETERMINISTIC
    CONTAINS SQL
    SQL SECURITY DEFINER
    COMMENT ''

BEGIN

DECLARE v_max int unsigned DEFAULT 100;
DECLARE v_counter int unsigned DEFAULT 0;
DECLARE cat_counter int unsigned DEFAULT 0;

  TRUNCATE TABLE `random`;
  START TRANSACTION;
  WHILE v_counter < v_max DO
    IF v_counter %10=0 THEN SET cat_counter=cat_counter+1;
    END IF;
    INSERT INTO `random` (question, category) VALUES ( CONCAT('Question', FLOOR(0 + (RAND() * 65535))), cat_counter );
    SET v_counter=v_counter+1;
  END WHILE;
  COMMIT;
END

注意:我尝试了所有答案,一切正常。 Gordon Linoff和pjanaway回答选择RANDOM只有前3或下3问题,我已经检查了Gordon的答案,因为他先回答,但这并不意味着其他答案都不好,所有这些都很好,这取决于用户选择正确答案或答案组合。我喜欢所有答案并将其投票。德鲁皮尔斯对这个问题的回答很新,现在更有趣,几乎接近目标。谢谢大家。

3 个答案:

答案 0 :(得分:5)

除了另一个答案,这也是另一种方法。

j

答案 1 :(得分:4)

是的,您可以通过枚举行然后获取前三个来完成此操作:

select r.id, r.question, r.category
from (select r.*,
             (@rn := if(@c = category, @rn + 1,
                        if(@c := category, 1, 1)
                       )
             ) as seqnum
      from `random` r cross join
           (select @rn := 0, @c := -1) params
      order by category, rand()
     ) r
where seqnum <= 3;

答案 2 :(得分:1)

create schema so_gibberish; -- creates database 
use so_gibberish;   -- use it 

-- drop table random;   -- during debug
create table random 
(   id int auto_increment primary key,
    question varchar(50) not null,
    category int not null,
    randomOrder int not null,
    key (category)
);

-- drop table questions_for_user;   -- during debug
create table questions_for_user 
(   physcOrder int auto_increment primary key,
    id int not null,
    question varchar(50) not null,
    category int not null,
    randomOrder int not null,
    key (category)
);

创建存储过程以插入随机问题。当你打电话时,它会一次创建300个。

DELIMITER $$ 
drop procedure if exists createRandomQuestions$$ 
-- 17 categories of questions randomly created. yes random word questions and categories.

create procedure createRandomQuestions()
BEGIN
set @i=1;
WHILE @i<=300 DO
insert random (question,category) values ('xxx',1);
SELECT @lid:=LAST_INSERT_ID();  -- use id to seed, next 8 guaranteed different i think

UPDATE random SET question=concat(
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@lid)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed:=round(rand(@seed)*4294967296))*36+1, 1),
substring('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', rand(@seed)*36+1, 1), ' ?'
), category=floor(rand()*17+1),randomOrder=0
WHERE id=@lid;
set @i=@i+1;
END WHILE;
END;
$$
DELIMITER ;

称之为:

call createRandomQuestions();

检查:

select category,count(*) from random group by category order by category;
select count(*) from random;
select * from random limit 10;

现在,根据请求为用户提供每个类别的三个随机问题。

提出一个好的随机SEEDING算法。以下是存根,最好使用http等服务等外部源。

update random set randomOrder=rand()*unix_timestamp();
truncate table questions_for_user;
insert into questions_for_user (id,question,category,randomOrder)
select id,question,category,randomOrder from random order by rand();

select r.* 
FROM questions_for_user r 
WHERE 
( SELECT COUNT(*) FROM random r1 WHERE r.category = r1.category AND r.id < r1.id ) <= 2 
ORDER by r.category ASC, randomOrder;

+------------+-----+------------+----------+-------------+
| physcOrder | id  | question   | category | randomOrder |
+------------+-----+------------+----------+-------------+
|        297 | 266 | JNQH26DD ? |        1 |   841700408 |
|        247 | 286 | ORK15577 ? |        1 |   980764662 |
|         54 | 267 | T2HPRW88 ? |        1 |  1331420535 |
|        190 | 275 | U5BFCUFF ? |        2 |   836160445 |
|        192 | 285 | E3KDJ144 ? |        2 |  1166207975 |
|         55 | 293 | GFWQ0BEE ? |        2 |  1356597807 |
|        266 | 296 | 8MJCWR55 ? |        3 |  1121232849 |
|        173 | 288 | 6GGOI2CC ? |        3 |  1209081435 |
|        205 | 231 | LQMYMV44 ? |        3 |  1330946482 |
|        103 | 289 | FUODJHJJ ? |        4 |   392498036 |
|        274 | 295 | Y85VNBWW ? |        4 |   613800522 |
|        204 | 280 | 441X1YTT ? |        4 |  1141251557 |
|        162 | 273 | CC5FGKFF ? |        5 |    99041401 |
|         36 | 252 | Y7V58ZEE ? |        5 |  1124240820 |
|        143 | 234 | DWZULKBB ? |        5 |  1286225785 |
|         15 | 276 | 3J1KGJZZ ? |        6 |    51285374 |
|        265 | 294 | PTEMZ7GG ? |        6 |   649256602 |
|         91 | 271 | TNG23R11 ? |        6 |  1393790410 |
|         90 | 277 | DXE1W0GG ? |        7 |   622567356 |
|         20 | 274 | LQTFS7RR ? |        7 |  1376505632 |
|        121 | 279 | VQN6TVSS ? |        7 |  1428714367 |
|        268 | 265 | A99UU1YY ? |        8 |   479923553 |
|        242 | 284 | 5PDRR5YY ? |        8 |   658551160 |
|        283 | 282 | NWZSPCZZ ? |        8 |   802197234 |
|        114 | 233 | 3IHU1YKK ? |        9 |   118146688 |
|         85 | 226 | BQTD6A44 ? |        9 |   292147382 |
|        255 | 291 | YNT0YN11 ? |        9 |   559911752 |
|        281 | 258 | IHK46577 ? |       10 |   196799301 |
|        198 | 263 | SHEVXPBB ? |       10 |   545833955 |
|         11 | 298 | QEHHSAEE ? |       10 |  1087006220 |
|         60 | 250 | GEH9PVBB ? |       11 |   225193615 |
|        270 | 272 | 3YY2EMM ?  |       11 |  1143544695 |
|        300 | 290 | O8B4WRCC ? |       11 |  1209867696 |
|         68 | 246 | FTEEVJ00 ? |       12 |   608441021 |
|        177 | 244 | X1JYHUBB ? |       12 |  1192309224 |
|        208 | 240 | W771N588 ? |       12 |  1347800170 |
|        249 | 300 | 97V6UXYY ? |       13 |   500846709 |
|        100 | 292 | 71JZTMQQ ? |       13 |   607266604 |
|         38 | 283 | WBQ0DGLL ? |       13 |  1187952919 |
|         87 | 235 | MBPPXJ44 ? |       14 |   327445349 |
|        178 | 242 | EZ1ET3ZZ ? |       14 |   852480639 |
|         62 | 281 | EIHVH3ZZ ? |       14 |  1420114728 |
|         95 | 251 | PT8E2CII ? |       15 |    72502146 |
|        170 | 253 | 8L35PFYY ? |       15 |  1091765038 |
|         65 | 287 | X5ZR3LHH ? |       15 |  1405199431 |
|        138 | 278 | MBW03OUU ? |       16 |    84358922 |
|          7 | 268 | 2G4G42WW ? |       16 |  1257379717 |
|          1 | 299 | ZT8QRRMM ? |       16 |  1327297420 |
|        221 | 297 | H00HLNRR ? |       17 |   890140945 |
|         40 | 204 | O7VUW2NN ? |       17 |  1238474743 |
|        122 | 229 | 3XEZG0PP ? |       17 |  1359337651 |
+------------+-----+------------+----------+-------------+
51 rows in set (0.01 sec)

为下一位用户或同一个人再次运行:

update random set randomOrder=rand()*unix_timestamp();
truncate table questions_for_user;
insert into questions_for_user (id,question,category,randomOrder)
select id,question,category,randomOrder from random order by rand();

select r.* 
FROM questions_for_user r 
WHERE 
( SELECT COUNT(*) FROM random r1 WHERE r.category = r1.category AND r.id < r1.id ) <= 2 
ORDER by r.category ASC, randomOrder;

+------------+-----+------------+----------+-------------+
| physcOrder | id  | question   | category | randomOrder |
+------------+-----+------------+----------+-------------+
|        112 | 286 | ORK15577 ? |        1 |   193281314 |
|        176 | 266 | JNQH26DD ? |        1 |   530153269 |
|        296 | 267 | T2HPRW88 ? |        1 |   891041924 |
|         37 | 293 | GFWQ0BEE ? |        2 |   222852606 |
|        239 | 285 | E3KDJ144 ? |        2 |   679635152 |
|        262 | 275 | U5BFCUFF ? |        2 |   846163956 |
|         95 | 288 | 6GGOI2CC ? |        3 |  1244253481 |
|         81 | 231 | LQMYMV44 ? |        3 |  1380298624 |
|         59 | 296 | 8MJCWR55 ? |        3 |  1420850554 |
|         28 | 295 | Y85VNBWW ? |        4 |   806083444 |
|         30 | 289 | FUODJHJJ ? |        4 |   814854070 |
|         34 | 280 | 441X1YTT ? |        4 |  1119188021 |
|        232 | 234 | DWZULKBB ? |        5 |   296692881 |
|        295 | 273 | CC5FGKFF ? |        5 |   337915901 |
|        140 | 252 | Y7V58ZEE ? |        5 |   644987638 |
|        257 | 271 | TNG23R11 ? |        6 |   619359840 |
|         27 | 294 | PTEMZ7GG ? |        6 |   869855570 |
|        218 | 276 | 3J1KGJZZ ? |        6 |  1390090875 |
|         64 | 279 | VQN6TVSS ? |        7 |    33942495 |
|        290 | 277 | DXE1W0GG ? |        7 |   100007602 |
|        173 | 274 | LQTFS7RR ? |        7 |   946909650 |
|        291 | 265 | A99UU1YY ? |        8 |   107468716 |
|         49 | 284 | 5PDRR5YY ? |        8 |  1068298164 |
|        228 | 282 | NWZSPCZZ ? |        8 |  1115906220 |
|        284 | 226 | BQTD6A44 ? |        9 |    45678738 |
|        179 | 291 | YNT0YN11 ? |        9 |   700305900 |
|        164 | 233 | 3IHU1YKK ? |        9 |  1416089612 |
|        193 | 258 | IHK46577 ? |       10 |   460111512 |
|        214 | 298 | QEHHSAEE ? |       10 |   482322673 |
|          7 | 263 | SHEVXPBB ? |       10 |   766681927 |
|        178 | 290 | O8B4WRCC ? |       11 |   341509950 |
|         31 | 272 | 3YY2EMM ?  |       11 |   726662739 |
|        297 | 250 | GEH9PVBB ? |       11 |  1386568968 |
|         32 | 240 | W771N588 ? |       12 |   303493686 |
|        283 | 246 | FTEEVJ00 ? |       12 |   710591266 |
|        177 | 244 | X1JYHUBB ? |       12 |   916685336 |
|        212 | 283 | WBQ0DGLL ? |       13 |   595739692 |
|        159 | 300 | 97V6UXYY ? |       13 |   688431139 |
|         52 | 292 | 71JZTMQQ ? |       13 |  1039681379 |
|         56 | 235 | MBPPXJ44 ? |       14 |   109832248 |
|        207 | 242 | EZ1ET3ZZ ? |       14 |   418951740 |
|          6 | 281 | EIHVH3ZZ ? |       14 |  1182157711 |
|        149 | 287 | X5ZR3LHH ? |       15 |   364819476 |
|         88 | 251 | PT8E2CII ? |       15 |   673475236 |
|        123 | 253 | 8L35PFYY ? |       15 |  1204512525 |
|        190 | 278 | MBW03OUU ? |       16 |   641720378 |
|        160 | 299 | ZT8QRRMM ? |       16 |  1289470813 |
|         75 | 268 | 2G4G42WW ? |       16 |  1427431541 |
|        202 | 297 | H00HLNRR ? |       17 |   374047531 |
|        243 | 204 | O7VUW2NN ? |       17 |   951026810 |
|        300 | 229 | 3XEZG0PP ? |       17 |  1319302198 |
+------------+-----+------------+----------+-------------+
51 rows in set (0.01 sec)

所以问题不同

以洗牌的方式获得最后的结果:

select r.* 
FROM questions_for_user r 
WHERE 
( SELECT COUNT(*) FROM random r1 WHERE r.category = r1.category AND r.id < r1.id ) <= 2 
ORDER by randomOrder;

+------------+-----+------------+----------+-------------+
| physcOrder | id  | question   | category | randomOrder |
+------------+-----+------------+----------+-------------+
|         64 | 279 | VQN6TVSS ? |        7 |    33942495 |
|        284 | 226 | BQTD6A44 ? |        9 |    45678738 |
|        290 | 277 | DXE1W0GG ? |        7 |   100007602 |
|        291 | 265 | A99UU1YY ? |        8 |   107468716 |
|         56 | 235 | MBPPXJ44 ? |       14 |   109832248 |
|        112 | 286 | ORK15577 ? |        1 |   193281314 |
|         37 | 293 | GFWQ0BEE ? |        2 |   222852606 |
|        232 | 234 | DWZULKBB ? |        5 |   296692881 |
|         32 | 240 | W771N588 ? |       12 |   303493686 |
|        295 | 273 | CC5FGKFF ? |        5 |   337915901 |
|        178 | 290 | O8B4WRCC ? |       11 |   341509950 |
|        149 | 287 | X5ZR3LHH ? |       15 |   364819476 |
|        202 | 297 | H00HLNRR ? |       17 |   374047531 |
|        207 | 242 | EZ1ET3ZZ ? |       14 |   418951740 |
|        193 | 258 | IHK46577 ? |       10 |   460111512 |
|        214 | 298 | QEHHSAEE ? |       10 |   482322673 |
|        176 | 266 | JNQH26DD ? |        1 |   530153269 |
|        212 | 283 | WBQ0DGLL ? |       13 |   595739692 |
|        257 | 271 | TNG23R11 ? |        6 |   619359840 |
|        190 | 278 | MBW03OUU ? |       16 |   641720378 |
|        140 | 252 | Y7V58ZEE ? |        5 |   644987638 |
|         88 | 251 | PT8E2CII ? |       15 |   673475236 |
|        239 | 285 | E3KDJ144 ? |        2 |   679635152 |
|        159 | 300 | 97V6UXYY ? |       13 |   688431139 |
|        179 | 291 | YNT0YN11 ? |        9 |   700305900 |
|        283 | 246 | FTEEVJ00 ? |       12 |   710591266 |
|         31 | 272 | 3YY2EMM ?  |       11 |   726662739 |
|          7 | 263 | SHEVXPBB ? |       10 |   766681927 |
|         28 | 295 | Y85VNBWW ? |        4 |   806083444 |
|         30 | 289 | FUODJHJJ ? |        4 |   814854070 |
|        262 | 275 | U5BFCUFF ? |        2 |   846163956 |
|         27 | 294 | PTEMZ7GG ? |        6 |   869855570 |
|        296 | 267 | T2HPRW88 ? |        1 |   891041924 |
|        177 | 244 | X1JYHUBB ? |       12 |   916685336 |
|        173 | 274 | LQTFS7RR ? |        7 |   946909650 |
|        243 | 204 | O7VUW2NN ? |       17 |   951026810 |
|         52 | 292 | 71JZTMQQ ? |       13 |  1039681379 |
|         49 | 284 | 5PDRR5YY ? |        8 |  1068298164 |
|        228 | 282 | NWZSPCZZ ? |        8 |  1115906220 |
|         34 | 280 | 441X1YTT ? |        4 |  1119188021 |
|          6 | 281 | EIHVH3ZZ ? |       14 |  1182157711 |
|        123 | 253 | 8L35PFYY ? |       15 |  1204512525 |
|         95 | 288 | 6GGOI2CC ? |        3 |  1244253481 |
|        160 | 299 | ZT8QRRMM ? |       16 |  1289470813 |
|        300 | 229 | 3XEZG0PP ? |       17 |  1319302198 |
|         81 | 231 | LQMYMV44 ? |        3 |  1380298624 |
|        297 | 250 | GEH9PVBB ? |       11 |  1386568968 |
|        218 | 276 | 3J1KGJZZ ? |        6 |  1390090875 |
|        164 | 233 | 3IHU1YKK ? |        9 |  1416089612 |
|         59 | 296 | 8MJCWR55 ? |        3 |  1420850554 |
|         75 | 268 | 2G4G42WW ? |       16 |  1427431541 |
+------------+-----+------------+----------+-------------+
51 rows in set (0.01 sec)

其他答案似乎返回相同问题(前3或后3)imo的原因是因为表的物理排序,这就是我创建第2个表的原因。第二个表使用新的虚假物理排序,并且插入到它中是通过随机顺序(因此物理顺序问题不存在)。希望这是有道理的。

当然,我挖走了pjanaway的答案,虽然我喜欢他的变量方法,却无法让Gordon在我的系统上工作。

祝你好运。