How do I use a value from the current form in my SQL Statement?

[josipradnik]

a) Take a look at demo app "example_dynamicautosuggest"
If you start typing Last Name, the autosuggestion from sql-statement fires as you type letter by letter
and dropdown list is shown dynamically using SQL:

proc page1_section1_field3_interactivechange()
    m_field = Lianja.get("page1.section1.field3")
    if len(m_field.value)!=0
        m_sql = "select last_name from example where last_name like '" + m_field.value + "%'"
    else
        m_sql = ""
    endif
    m_field.autosuggest = m_sql
endproc

In this case formfield is used as a "standalone"
If you are not testing len(m_field.value), you could write:

m_sql = "select last_name from example where last_name like '" + Lianja.get("page1.section1.field3").value + "%'"

In your case:

m_sql = "SELECT firstname FROM userlookup WHERE userid =  '"+Lianja.get("page1.section1.useridontheform").value+"'"

Note that we build the string.

b) If your form is database binded (see demo app "example_virtualtables")
you should use macro with table/column name like that in "SQL statement" attribute of section2

select * from orders where customerid='{vcust.customerid}'

Child Section2 (grid) is populated indirectly with data from the parent Section1's formfield page1.section.field1,
in fact from underlying table vcust and column customerid.

In your case:

SELECT firstname FROM userlookup WHERE userid = '{yourtable.column_under_useridontheform}'

Note that we write into section's attribute.