如何使用唯一的随机序列号更新MySQL表列？

Question

I try to update my MySQL table column, and set random sequence number, begin from 1,2,3,etc. For example, I have total 38 row, so i need update it with number 1-38 (can't duplicate). i tried using:

UPDATE TABLE SET VALUE=FLOOR(RAND()*38)+1

but it gives me some duplicate number, i need every rows have different number.

Answer 1

You can try something like this:

SET @r := 0;
UPDATE  table
SET     value = (@r := @r + 1)
ORDER BY
        RAND();

This will assign numbers 1 to 38 would be assigned randomly and uniquely.

SQLFiddle

Hope this helps!!!

Answer 2

Might not be exactly what you want, but if you are looking towards assigning unique ID starting from 1 to your table, architectally good solution would be making your 'id' column an auto incrementing unique number:

ALTER TABLE TABLE_NAME ADD COLUMN_NAME INT PRIMARY KEY AUTO_INCREMENT;

If you already have the column, you could previously remove it:

ALTER TABLE TABLE_NAME DROP COLUMN_NAME

Answer 3

• Step 1 : Do a for loop and store all 38 numbers in an array.
• Step 2 : shuffle that array using shuffle function. http://php.net/manual/en/function.shuffle.php
• Step 3 : Do a Foreach loop for that shuffled array and update your column.

Just example code:

  for($i=1;$i<=38;$i++)
  {
     $arr[$i] = $i;
  }

  shuffle($arr);

  foreach($arr as $randarray)
  {
     //Your SQL query here UPDATE TABLE SET VALUE=$randarray like that
  }

Answer 4

If you want a solution only in MySQL you need something like this:

update test set id =  (select MAX(id)+1 from test)  WHERE <your_condition>

But you will get error:

You can't specify target table 'test' for update in FROM clause

So you have to do something like that to avoid this error:

    update test set 
    id =  ( 
     select maxPlus1 from 
      (
       select MAX(id)+1 as maxPlus1 
       from test
      ) 
      maxTable
     ) WHERE <your_condition>