PHP SQL Subtraction in Query?

3 Comments

• catbertnc

  June 7, 2010 at 7:29 am

  Try setting valueA to a variable, and doing the math in code. Then write the result to the database.

• General Cucombre

  June 7, 2010 at 7:31 am

  Remove the quotes around $valueB in your query. If you’re doing math on numbers, you don’t need them:

  …
  mysql_query(“UPDATE values SET valueA = valueA – $valueB”);

  useful tip – if $value comes from elsewhere and you’re not sure if it is numeric or non-empty, do this before query:

  $valueB += 0;

• 404

  June 7, 2010 at 8:12 am

  if there is only 1 value in the sql table and if you dont escape from sytnax errors with anyway.
  usethis code

  $valueB = 5;
  $valueA = mysql_query (“select valueA from values”);
  $valueA = mysql_result($valueA,”valueA”,0);
  $valueA = $valueA – $valueB;
  $sql = mysql_query(“UPDATE values SET valueA = valueA – ‘$valueB’”);