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mysql随机数怎么设置 mysql生成随机字符串

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MySQL产生随机数MYSQL 取随机数
2010年04月26日 星期一 09:48
mysql 取随机数
--对一个表取任意随机数
SELECT *
FROM TMP_XF_TEST
WHERE ID = (SELECT FLOOR(RAND() * (SELECT MAX(ID) FROM TMP_XF_TEST)))
order by id LIMIT 1;
--有条件性的取随机数
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;
#########
不要用下面的杯具写法
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: 165888Duplicates: 0Warnings: 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 | 玄风|9 |123 | 2010-04-26 14:56:39 | 2010-04-26 14:56:39 | 玄风测试使用的数据 |
+-----+-----------+-----+---------+---------------------+---------------------+--------------------+
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 | 玄风|9 |123 | 2010-04-28 15:47:19 | 2010-04-28 15:47:19 | 玄风测试使用的数据 | 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 | 玄风|9 |123 | 2010-04-28 15:47:19 | 2010-04-28 15:47:19 | 玄风测试使用的数据 |

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