The Syntax is correct, but somehow it doesn't work at all how it was planned. My plan was to search an specific value in the Column 'Mtart'. When its true boolean should be 'true' too. But it doesnt. Could you help me with this too?
Would you be able to share a sample where I can see what you have? I am just seeing half of the script and that to without knowing your data... if you can mock up your scenario for me, I should be able to help you better
You could use the following to detect if a certain value exists within the datamodel:
let boolean = if(fieldindex('Mtart_G', 151), dual('true', 1), dual('false', 0));
If you need to check this by key-fields within a certain table you will need to ensure a certain order of your loadings or you need to load it from this table - whereby in this case the check might be already done within the origin load.