# MySQL/MariaDB plugin does not seem to notice error signals

**URL:** <https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944>\
**Category:** Databases\
**Created:** [September 29, 2026, 5:35pm UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944 "2026-09-29T17:35:36Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Thom\_McGrath](https://forum.xojo.com/user_avatar/forum.xojo.com/thom_mcgrath/32/192_2.png) [@Thom\_McGrath](https://forum.xojo.com/u/Thom_McGrath)\
**Post date:** [September 29, 2026, 5:35pm UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/1 "2026-09-29T17:35:36Z")

</div>

I’m no expert on this database… I really dislike it, but it’s not my choice… so I’m definitely no expert. I’m trying to throw an exception inside a function, but Xojo is ignoring it. I use a line like:

```sql
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'This is an error.';

```

And in Xojo will use

```xojo
db.ExecuteSQL("SELECT function_name();")

```

And I don’t get a DatabaseException from Xojo. The Xojo code continues, but the database function (correctly) does not complete.

Do I need to raise the exception some other way for Xojo to react?

---

<div class="post-metadata">

**Author:** ![Andrew\_Paul\_Dickey](https://forum.xojo.com/letter_avatar_proxy/v4/letter/a/82dd89/32.png) [@Andrew\_Paul\_Dickey](https://forum.xojo.com/u/Andrew_Paul_Dickey)\
**Post date:** [September 29, 2026, 10:34pm UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/2 "2026-09-29T22:34:12Z")

</div>

@Thom_McGrath,

I will confirm, but this is either the database library ignoring signal raised inside functions or an issue with certain versions of MariaDb.

I think what you are attempting is the ‘correct’ modern way using ‘signal’.

```auto
DELIMITER //

CREATE FUNCTION GetUserAge(birth_date DATE)
RETURNS INT
DETERMINISTIC
BEGIN
    -- Check if the birth date is in the future
    IF birth_date > CURDATE() THEN
        SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'Invalid date: Birth date cannot be in the future.';
    END IF;

    RETURN TIMESTAMPDIFF(YEAR, birth_date, CURDATE());
END //

DELIMITER ;

```

However, If that is not working as expected for you from within Xojo, there is a universal fallback to force a deliberate native database error, which you should be able to catch in Xojo:

```auto
DELIMITER //

CREATE FUNCTION DivideNumbers(numerator DECIMAL(10,2), denominator DECIMAL(10,2))
RETURNS DECIMAL(10,2)
DETERMINISTIC
BEGIN
    -- If denominator is zero, force an error to stop execution
    IF denominator = 0 THEN
        -- This will fail immediately and return a native MariaDB error
        TRUNCATE TABLE `ERROR: Cannot divide by zero`;
    END IF;

    RETURN numerator / denominator;
END //

DELIMITER ;

```

Maybe use something less dramatic than truncate table though…

Then, without trying to sound patronising (you are a far better dev than I am)…

```auto
Try
  ' try and run your function
Catch e As DatabaseException
  ' do something with e
End Try

```

Note in the second case, you still get to set custom error message text.

I hope that helps.

Kind regards, Andrew

---

<div class="post-metadata">

**Author:** ![Thom\_McGrath](https://forum.xojo.com/user_avatar/forum.xojo.com/thom_mcgrath/32/192_2.png) [@Thom\_McGrath](https://forum.xojo.com/u/Thom_McGrath)\
**Post date:** [September 29, 2026, 11:07pm UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/3 "2026-09-29T23:07:11Z")

</div>

Yeah you’ve got exactly the right idea. Catching the error with a try block is precisely what I want to do. But Xojo isn’t firing an exception, so there is nothing to catch.

The workaround I’ve had to use is a useless return value in the executed function. If I get the expected value, I know it worked. If I get null, it must have failed. I can’t get the message, but it’s at least something.

---

<div class="post-metadata">

**Author:** ![Andrew\_Paul\_Dickey](https://forum.xojo.com/letter_avatar_proxy/v4/letter/a/82dd89/32.png) [@Andrew\_Paul\_Dickey](https://forum.xojo.com/u/Andrew_Paul_Dickey)\
**Post date:** [September 30, 2026, 6:35am UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/4 "2026-09-30T06:35:03Z")

</div>

@Thom_McGrath, I tried a few variations inside Functions in MariaDb. All techniques throw errors correctly in Navicat Premium Lite (database client), but are ignored as DatabaseExceptions in Xojo.

So I suggest you convert your Functions (that return a value or values) to Stored Procedures (that return a value or values).

From my example this morning.

```auto
DELIMITER //

CREATE PROCEDURE CalculateDiscountProc(
    IN price DECIMAL(10,2), 
    IN discount_pct INT,
    OUT final_price DECIMAL(10,2) -- This parameter returns the value
)
BEGIN
    -- Standard, clean error signaling (No workarounds needed!)
    IF discount_pct > 100 THEN
        SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'ERROR: Discount percent cannot exceed 100%';
    END IF;

    -- Perform the calculation and assign it to the OUT variable
    SET final_price = price - (price * (discount_pct / 100));
END //

DELIMITER ;

```

I can’t remember why, but at some stage, I began favouring stored procedures because they reported errors correctly.

```auto
Try
  db.ExecuteSQL("CALL CalculateDiscountProc(" + tfAmount.Text + "," + tfDiscount.Text + ",@result)")
  Var rs AS RowSet = db.SelectSQL("SELECT @result")
  TextArea1.Text = rs.ColumnAt(0).StringValue
Catch e As DatabaseException
  TextArea1.Text = e.Message
End Try

```

You can see the error being caught in the debugger.

![Screenshot 2026-09-30 at 4.31.26 pm](https://forum.xojo.com/uploads/default/original/3X/2/3/2357217c4069d7fccc7a6678af28c4b8f68c1c4b.png)

At least now you can catch errors as DatabaseExceptions, with roughly the same workflow as Functions.

I hope that helps.

Kind regards, Andrew

---

<div class="post-metadata">

**Author:** ![Thom\_McGrath](https://forum.xojo.com/user_avatar/forum.xojo.com/thom_mcgrath/32/192_2.png) [@Thom\_McGrath](https://forum.xojo.com/u/Thom_McGrath)\
**Post date:** [September 30, 2026, 11:59am UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/5 "2026-09-30T11:59:07Z")

</div>

Thank you, this is very helpful!

---

<div class="post-metadata">

**Author:** ![Rick\_Araujo](https://forum.xojo.com/user_avatar/forum.xojo.com/rick_araujo/32/251_2.png) [@Rick\_Araujo](https://forum.xojo.com/u/Rick_Araujo)\
**Post date:** [September 30, 2026, 7:31pm UTC](https://forum.xojo.com/t/mysql-mariadb-plugin-does-not-seem-to-notice-error-signals/88944/6 "2026-09-30T19:31:49Z")

</div>

> [@Andrew\_Paul\_Dickey](#):
>
> ```auto
> Try
> db.ExecuteSQL("CALL CalculateDiscountProc(" + tfAmount.Text + "," + tfDiscount.Text + ",@result)")
> Var rs AS RowSet = db.SelectSQL("SELECT @result")
> TextArea1.Text = rs.ColumnAt(0).StringValue
> Catch e As DatabaseException
> TextArea1.Text = e.Message
> End Try
> 
> ```

Maybe it works with stored functions instead of stored procs?

So you could do something more direct as:

```auto
DELIMITER //

CREATE FUNCTION CalculateDiscountFunc(
    price DECIMAL(10,2), 
    discount_pct INT
)
RETURNS DECIMAL(10,2)
DETERMINISTIC
BEGIN
    -- Standard error signaling works the same way in functions
    IF discount_pct > 100 THEN
        SIGNAL SQLSTATE '45000'
        SET MESSAGE_TEXT = 'ERROR: Discount percent cannot exceed 100%';
    END IF;

    -- Perform the calculation and return the value directly
    RETURN price - (price * (discount_pct / 100));
END //

DELIMITER ;

```

And simpler to use as:

```auto
Try

  Var calcParms As String = tfAmount.String + " , " + tfDiscount.String
  Var sql As String = "SELECT CalculateDiscountProc(" + calcParms + ") As result;")

  Var rs AS RowSet = db.SelectSQL(sql)

  TextArea1.Text = rs.ColumnAt(0).StringValue

Catch e As DatabaseException

  TextArea1.Text = e.Message

End Try

```

And yes, I use Functions to return some special columns I do calculate