a #GdaConnection object
a partial SQL statement which is the context of the completion proposal
starting position within sql of the "token" to complete (starts at 0)
ending position within sql of the "token" to complete
a new array of strings, or null (use glib.global.strfreev to free the returned array)
Creates an array of strings (terminated by a null) corresponding to possible completions. If no completion is available, then the returned array contains just one NULL entry, and if it was not possible to try to compute a completions list, then null is returned.