MySQL產(chǎn)生隨機(jī)數(shù)

MYSQL 取隨機(jī)數(shù)

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2010年04月26日 星期一 09:48

mysql 取隨機(jī)數(shù)

--對(duì)一個(gè)表取任意隨機(jī)數(shù)

SELECT *

FROM TMP_XF_TEST

WHERE ID = (SELECT FLOOR(RAND() * (SELECT MAX(ID) FROM TMP_XF_TEST)))

order by id LIMIT 1;

--有條件性的取隨機(jī)數(shù)

SELECT *

FROM TMP_XF_TEST

WHERE ID = (SELECT FLOOR(RAND() *

((SELECT MAX(ID) FROM TMP_XF_TEST WHERE GID = 9) -

(SELECT MIN(ID) FROM TMP_XF_TEST WHERE GID = 9))) +

(SELECT MIN(ID) FROM TMP_XF_TEST WHERE GID = 9))

AND GID = 9

ORDER BY ID LIMIT 1;

--gid上存在索引

或者

SELECT *

FROM TMP_XF_TEST AS t1 JOIN

(SELECT ROUND(RAND() * ((SELECT MAX(id) FROM TMP_XF_TEST WHERE GID = 9)-(SELECT MIN(id) FROM TMP_XF_TEST WHERE GID = 9))

+(SELECT MIN(id) FROM TMP_XF_TEST WHERE GID = 9)) AS id) AS t2

WHERE t1.id = t2.id AND t1.GID = 9

ORDER BY t1.id LIMIT 1;

#########

不要用下面的杯具寫(xiě)法

mysql insert into tmp_xf_test(user_nick,gid,item_id,gmt_create,gmt_modified,memo)

- select user_nick,gid,item_id,gmt_create,gmt_modified,memo from tmp_xf_test;

Query OK, 165888 rows affected (9.65 sec)

Records: 165888 Duplicates: 0 Warnings: 0

mysql SELECT *

- FROM `tmp_xf_test`

- WHERE id = (SELECT FLOOR( MAX(id) * RAND()) FROM `tmp_xf_test` )

- ORDER BY id LIMIT 1;

+-----+-----------+-----+---------+---------------------+---------------------+--------------------+

| id | user_nick | gid | item_id | gmt_create | gmt_modified | memo |

+-----+-----------+-----+---------+---------------------+---------------------+--------------------+

| 467 | 玄風(fēng) | 9 | 123 | 2010-04-26 14:56:39 | 2010-04-26 14:56:39 | 玄風(fēng)測(cè)試使用的數(shù)據(jù) |

+-----+-----------+-----+---------+---------------------+---------------------+--------------------+

1 row in set (51.12 sec)

mysql explain SELECT *

- FROM `tmp_xf_test`

- WHERE id = (SELECT FLOOR( MAX(id) * RAND()) FROM `tmp_xf_test` )

- ORDER BY id LIMIT 1\G

*************************** 1. row ***************************

id: 1

select_type: PRIMARY

table: tmp_xf_test

type: index

possible_keys: NULL

key: PRIMARY

key_len: 8

ref: NULL

rows: 1

Extra: Using where

*************************** 2. row ***************************

id: 2

select_type: UNCACHEABLE SUBQUERY

table: tmp_xf_test

type: index

possible_keys: NULL

key: idx_tmp_xf_test_gid

key_len: 4

ref: NULL

rows: 331954

Extra: Using index

2 rows in set (0.01 sec)

---

mysql SELECT * FROM `tmp_xf_test` t1 join

- (SELECT FLOOR( MAX(id) * RAND()) as id FROM `tmp_xf_test` ) as t2

- where t1.id =t2.id

- ORDER BY t1.id LIMIT 1;

+-------+-----------+-----+---------+---------------------+---------------------+--------------------+-------+

| id | user_nick | gid | item_id | gmt_create | gmt_modified | memo | id |

+-------+-----------+-----+---------+---------------------+---------------------+--------------------+-------+

| 40311 | 玄風(fēng) | 9 | 123 | 2010-04-28 15:47:19 | 2010-04-28 15:47:19 | 玄風(fēng)測(cè)試使用的數(shù)據(jù) | 40311 |

+-------+-----------+-----+---------+---------------------+---------------------+--------------------+-------+

1 row in set (0.14 sec)

##############

mysql SELECT * FROM `tmp_xf_test`

- WHERE id = (SELECT floor(RAND() * (SELECT MAX(id) FROM `tmp_xf_test`)))

- ORDER BY id LIMIT 1;

+------+-----------+-----+---------+---------------------+---------------------+--------------------+

| id | user_nick | gid | item_id | gmt_create | gmt_modified | memo |

+------+-----------+-----+---------+---------------------+---------------------+--------------------+

| 1352 | 玄風(fēng) | 9 | 123 | 2010-04-28 15:47:19 | 2010-04-28 15:47:19 | 玄風(fēng)測(cè)試使用的數(shù)據(jù) |

+------+-----------+-----+---------+---------------------+---------------------+--------------------+

1 row in set (0.00 sec)

mysql explain SELECT * FROM `tmp_xf_test`

- WHERE id = (SELECT floor(RAND() * (SELECT MAX(id) FROM `tmp_xf_test`)))

- ORDER BY id LIMIT 1\G

*************************** 1. row ***************************

id: 1

select_type: PRIMARY

table: tmp_xf_test

type: index

possible_keys: NULL

key: PRIMARY

key_len: 8

ref: NULL

rows: 1

Extra: Using where

*************************** 2. row ***************************

id: 3

select_type: SUBQUERY

table: NULL

type: NULL

possible_keys: NULL

key: NULL

key_len: NULL

ref: NULL

rows: NULL

Extra: Select tables optimized away

2 rows in set, 1 warning (0.00 sec)

對(duì)應(yīng)的另外一種杯具寫(xiě)法是：

SELECT *

FROM TMP_XF_TEST

WHERE ID = (SELECT FLOOR(RAND() * (MAX(ID) - MIN(ID))) + MIN(ID) MID

FROM TMP_XF_TEST

WHERE GID = 9)

AND GID = 9 LIMIT 1;

mysql如何生成不重復(fù)的隨機(jī)數(shù)

mysql的rand函數(shù)可以生成一個(gè)0到1之間的隨機(jī)數(shù)，進(jìn)行一定的放大即可得到一個(gè)隨機(jī)數(shù)。再通過(guò)條件查詢來(lái)限制新隨機(jī)數(shù)沒(méi)有在表中出現(xiàn)過(guò)。如下所示：

SELECT FLOOR(RAND() * 99999) AS random_numFROM numbers

WHERE "random_num" NOT IN (SELECT my_number FROM numbers)

LIMIT 1

mysql怎么生成不重復(fù)的隨機(jī)數(shù)

MySql數(shù)據(jù)庫(kù)隨機(jī)函授Rand()可以產(chǎn)生0~1之間帶小數(shù)的隨機(jī)數(shù)，只要將括號(hào)中的參數(shù)留空，所產(chǎn)生的數(shù)是完全隨機(jī)的，出現(xiàn)重復(fù)的幾率不大，但是不可避免會(huì)有重復(fù)的可能，如果需要完全避免重復(fù)，可以先用隨機(jī)函數(shù)產(chǎn)生一堆數(shù)字，然后用剔除其中的重復(fù)數(shù)這個(gè)辦法來(lái)實(shí)現(xiàn)。

例如先用循環(huán)產(chǎn)生一批隨機(jī)數(shù)并存入數(shù)據(jù)表中，再用

select distinct colName from tableName;

選出無(wú)重復(fù)的隨機(jī)數(shù)予以應(yīng)用

如何通過(guò)java向mysql輸入一個(gè)隨機(jī)數(shù)猜大小

1、首先通過(guò)控制臺(tái)一直輸入一個(gè)整數(shù)，比較該數(shù)與系統(tǒng)隨機(jī)生成的那個(gè)數(shù)。

2、其次如果大就輸出“猜大了。”，繼續(xù)輸入。如果小就輸出“猜小了?！?。

3、最后繼續(xù)輸入；如果相等就輸出“恭喜，猜對(duì)了?！保顺鲚敵?。