Question

Im trying to count the number of rows in the table and generate random numbers for the field ‘random’
Now this works:

SELECT COUNT(*) FROM my_table; 

and this works:

   UPDATE my_table SET random = FLOOR(6500 * RAND()) + 1;

But this doesn’t work:

UPDATE my_table SET random = FLOOR((SELECT COUNT(*) ) * RAND()) + 1;

But this counts the rows as 0 and adds one so all fields have the number one instead of a unique random number.

Any ideas what I’m doing wrong would be most helpful.

Answer 1

What about this?

SELECT @cnt := count(*) FROM my_table;
UPDATE my_table SET random = FLOOR(@cnt * RAND()) + 1;

Demo: http://sqlfiddle.com/#!2/a896d/4