How to implement a random number using the MySQL rand function

In mysql, can I use a random number to write a statement to update hundreds of MYSQL Data Records? The answer is yes. Using the MySQL rand function, we can make the current random number.

To test the MYSQL database, there is a database with tens of thousands of data records. How to Write a PHP file and update several hundred pieces of information each time? I write a loop to update one piece of information at a time, in this way, I can use WHILE to write data. If an update is like 100 data records, how can I write it! The correct answer is to use the MySQL rand function: UPDATE cdb_posts SET views = rand (); By the way, I found an instance of the mysql rand function, as shown below: In the insert command, rand () is used in value (). If the field width is sufficient, you can SELECT * FROM 'table' order by rand () LIMIT 5.
You can.

However, the test results show that the efficiency is very low. It takes more than 8 seconds for a database with more than 0.15 million records to query 5 data records. It also means that rand () will be executed multiple times in the order by clause, natural efficiency and low ..

Search for Google. Basically, data is randomly obtained by querying max (id) * rand () on the Internet. SELECT *
FROM 'table' AS t1 JOIN (select round (RAND () * (select max (id) FROM 'table') AS id) AS t2
WHERE t1.id> = t2.id
Order by t1.id asc limit 5;

However, five consecutive records are generated. The solution is to query only one item at a time and query five times. Even so, it is worthwhile because it takes less than 0.15 million seconds to query 0.01 tables. The preceding statement uses JOIN, and someone on the mysql Forum uses SELECT *
FROM 'table'
WHERE id> = (select floor (MAX (id) * RAND () FROM 'table ')
Order by id LIMIT 1;

I tested it. It took 0.5 seconds and the speed was good, but there was still a big gap with the above statements. I always feel that something is abnormal. So I changed the statement.

SELECT * FROM 'table'
WHERE id> = (SELECT floor (RAND () * (select max (id) FROM 'table ')))
Order by id LIMIT 1;

Now, the efficiency is improved. The query time is only 0.01 seconds, and then the statement is improved, plus the MIN (id) judgment. At the beginning of the test, because I did not add the MIN (id) Judgment, half of the time is always the first few rows in the table.
The complete query statement is:
SELECT * FROM 'table'
WHERE id> = (SELECT floor (RAND () * (select max (id) FROM 'table')-(select min (id) FROM 'table ')) + (select min (id) FROM 'table ')))
Order by id LIMIT 1;
SELECT *
FROM 'table' AS t1 JOIN (select round (RAND () * (select max (id) FROM 'table')-(select min (id) FROM 'table ')) + (select min (id) FROM 'table') AS id) AS t2
WHERE t1.id> = t2.id
Order by t1.id LIMIT 1;
Finally, these two statements are queried 10 times in php respectively,
The former takes 0.147433 seconds.
The latter takes 0.015130 seconds.

The preceding method is used to implement random numbers using the MySQL rand function.

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