将变量从数据库表列获取到基于选项字段中选定选项的输入字段

Question

I have succesfully retrieved two columns from my table and displayed the result as options in a select tag, in my form.

The problem is I cannot display the data from a third column into an input field, which is also in the form, based on the selected option.

There is no issue with the database connection or retrieving the data for the options in the select tag.

Any help would be appreciated. The relevant code is below.

     <div class="col-md-4 col-12 bottommargin-sm">
      <label for="">Choose currency</label>
      <select class="form-control" id="exampleFormControlSelect1">

        <option value="">Choose currency...</option>

        <?php

        // Including DB connection file
        include_once "config/config.php";

        // Retrieving all columns from currency table
        $result = mysqli_query($con, "SELECT * FROM currency_test");

        // Loop printing options with country and currrency for all rows in currency table
        while($row = mysqli_fetch_array($result)) {

          print "<option>";

          echo $row['country'] . " - " . $row['currency'];

          print "</option>";

        }

        // Closing DB connection
        mysqli_close($con);

        ?>

      </select>
    </div>

    <div class="col-md-2 col-12 bottommargin-sm">
      <label for="">Currency rate</label>
      <input type="text" class="form-control" value="<?php echo $row['buy_rate'] ?>" readonly>
    </div>

Additional Edit

I am now using the following code, still without any luck:

     <div class="col-md-4 col-12 bottommargin-sm">
      <label for="">Choose currency/label>
      <select class="form-control" id="exampleFormControlSelect1">

        <option value="default">Choose currency...</option>

        <?php

        // Including DB connection file
        include_once "config/config.php";

        // Retrieving all columns from currency table
        $result = mysqli_query($con, "SELECT * FROM currency_test");

        // Loop printing country, currrency, buy_rate and sell_rate for all rows in currency table
        while($row = mysqli_fetch_array($result)) {

          echo "<option value=".$row['currency']."> ".$row['country']. " - " .$row['currency']." </option>";

        }

        ?>

      </select>
    </div>

    <div class="col-md-2 col-12 bottommargin-sm">
      <label for="">Currency rate</label>
      <input type="text" class="form-control" value="<?php echo $row['buy_rate'] ?>" readonly>
    </div>

    <?php

    // Closing DB connection
    mysqli_close($con);

    ?>

Answer 1

As said before, you have a result SET in your while-loop above, but you want the input field only to contain a single value: the buy-rate of the selected currency. If I guessed right and this is what you want, this will not work like this.

If you want to test it and just retrieve only a single value in your while-loop, also your input field gets filled with the correct buy-rate.

You can do it with or without JavaScript, but you need a second statement to retrieve the buyrate you desire.

Further security suggestions: You should not use the include directives without __ DIR __ . Neither you should use "SELECT * ...". Better it is to name all the fields you want to retrieve.

Answer 2

You will have to have a statement for that selection. (Hint: Also in the tag you will have to have a value attribute set) Also your select needs a name if you use a submit button..

Now when you submit the form you can query the database and show the correct record.

If you dont want to use a submit button and have the value in the textfield change by selection, you will need javascript.

Answer 3

So what I see :

1) No name in select tag

<select class="form-control" id="exampleFormControlSelect1">

There is no name attribute. So after posting the form, the server doesn't know the name of the variable.

2) No value

print "<option>";

You don't supply a value. So your server doesn't know the value (the user selected) after posting the form.

This is the proper way for a select tag : https://www.w3schools.com/tags/tag_select.asp