Report Execution Error for invalid SQL query when adding filter with comparison operator "Does Not Begin With"

I am receiving a Report Execution Error when adding a filter with comparison operator "Does Not Begin With". In this case I used ItemCode does not begin with G, however, I have tried on different expressions and have issues each time. I am not very familiar with how SQL works, but the statement seems to be looking for the entire value to not be like G? Below is the SQL Debugger results.


What I'd like to know is:

1. Are there limitations to which expressions the Does Not Begin With operator can be used with?

2. Is there a workaround to filtering out results that begin with a specified character? (before generating the report)

3. Is there documentation that details any limitations that comparison operators have in filtering/parameters?