mysql - execute SELECT query only when TABLE EXIST - mysql

Question

I am working on a Joomla Module where images can be shown and be linked to a Joomla Article, Virtuemart product or an external link.
To have to option to select a Virtuemart Product, I added the following parameter to the module manifest xml:
<field
name="image_1_product"
type="sql"
default="10"
query="SELECT #__virtuemart_products.virtuemart_product_id, #__virtuemart_products_en_gb.product_name
FROM #__virtuemart_products, #__virtuemart_products_en_gb
WHERE #__virtuemart_products.virtuemart_product_id = #__virtuemart_products_en_gb.virtuemart_product_id
AND #__virtuemart_products.published = 1"
key_field="virtuemart_product_id"
value_field="product_name"
label="LABEL_PRODUCT"
description="DESC_PRODUCT">
</field>
This works just fine, when Virtuemart is installed. When Virtuemart is not installed, you get an error 'Unknown column' - which makes sense.
Because this is a Module Manifest Option, I can use only 1 query. Is there a way to run a query that checks if a table exists before it executes the select? Like:
IF EXISTS TABLE `table_a` (SELECT * FROM table_a)
If so, can it return a row like:
| id | value |
| 0 | Virtuemart not found |
Thank you!

Answer 1

I'm afraid its not possible with just single database query.
The only workaround that I can think of is to create a parameter helper for your module and use an addfieldpath to your module fieldset tag. With this solution you can write an method to do the query and create the output, then you can check if the table exists or not before creating your parameter.
for example:
<config>
<fields name="params">
<fieldset name="basic" addfieldpath="/modules/mod_mymodule/elements/">
<field name="image_1_product" type="product" default="10" label="LABEL_PRODUCT" description="DESC_PRODUCT"/>
</fieldset>
</fields>
</config>
now in /modules/mod_mymodule/elements/ create a PHP file named product.php and write your custom query and field descriptions as described in Joomla's documentation.
Joomla documentation is available for Custom parameter types and Creating custom template parameter types