Question

I have a mysql table.

I want to “cut and paste” a value from one column to another using php. like this:

mysql_query("UPDATE table1 SET a1=a2,a2='' WHERE colid=3 LIMIT 1");

Is it possible to do this with just a single statement as above?

Does the ordering of the elements used in “SET” part matter?

If this is not good, what is the most efficient way to do this?

Answer 1

From the docs:

The second assignment in the following statement sets col2 to the current (updated) col1 value, not the original col1 value. The result is that col1 and col2 have the same value. This behavior differs from standard SQL.

UPDATE t1 SET col1 = col1 + 1, col2 = col1;

Single-table UPDATE assignments are generally evaluated from left to right. For multiple-table updates, there is no guarantee that assignments are carried out in any particular order.