插入新列，递增所有行

Question

Is this possible using only mysql:

Insert a new column and example - "pos". Every row in the table has to have unique,incresing value of "pos" like - 1,2,3,4,5.

In php this would be an easy job:

$query = "SELECT * FROM example"; 

$result = mysql_query($query) or die(mysql_error());

$counter = 0;
while($row = mysql_fetch_array($result)){
    mysql_query( "UPDATE example SET pos = ".++$counter." WHERE id = ".$row['id']." );
}

Answer 1

是的，你可以这样做

    UPDATE example SET pos = pos+1  WHERE id = ".$row['id']."

Answer 2

As already suggested, the most efficient solution is to use auto incremental on pos.

Alternatively if your use case do not permit you, then try similar:

"UPDATE example SET pos = ((select max(pos) from example) +1) WHERE id
= ".$row['id']."

Answer 3

为你的pos mysql字段提供auto_increment属性 - 这将对其进行索引，使其唯一，并在每个插入上递增1