Though if you want to make a field optional in an `INSERT` statement, you need to get a little fancy. Metabase will only run an optional statement if a value is supplied to a variable in that optional statement, so the trick here is to use a SQL comment to sneak a variable into the optional column.
```
{% raw %}
[[,expected_invoice -- {{ expected_invoice}}]]
{% endraw %}
```
So a full `INSERT` statement with an optional variable would look like so (note that the optional clauses for the `{% raw %}{{ expected_invoice}}{{% endraw %}` variable are in both the column and values lists):
```
{% raw %}
INSERT INTO invoices (
account_id
,payment
[[,expected_invoice -- {{expected_invoice}}]]
,plan
,date_received
)
VALUES (
{{ account_id }}
,{{ payment }}
[[,{{ expected_invoice }}]]
,{{ plan }}
,({{ date_received }}
);
{% endraw %}
```
### Casting field values in actions
If you get a type error when you submit a form, you may need to `CAST` the data type in the query so it matches the data type of the target field in the database. Here we're casting a value to a `boolean`:
