存储来自 SQL 表的变量，以便稍后使用 PHP

Question

I would like to be able to store a variable from a column to use to update a variable in another column.

Here is my code:

        $sqlPlaceNumber = "SELECT @locationPlace := `$locationPlace` FROM `$className` WHERE `Vehicle` = `$vehicleName` ";
        $results = mysqli_query($con, $sqlPlaceNumber) or die(mysqli_error($con));

        $sqlUpdate = "UPDATE `$className` SET `$location` = 31-`@locationPlace` WHERE Vehicle = `$vehicleName`";
        mysqli_query($con, $sqlUpdate) or die(mysqli_error($con));

I would like to store the value of column "Colby, WI Place" to use to subtract it from 31 to get the value for column "Colby, WI"

31-"Colby, WI Place" = new value for "Colby, WI"

Answer 1

It looks like you want:

update mytable set `Colby, WI` = 31 - `Colby, WI Place` where vehicle = ?

There is no need to use an intermediate variable, you can do this what you want with a single update statement.

Also I would strongly recommend using column names that do not contain special characters (they should be made of alphanumeric characters and underscores only), so you don't need to worry about quoting them.

Finally: you do want to use parameterized queries to make your code safer and more efficient. You can have a look at this post for more information.