sql-3-insert test: string's length must be checked when inserted into a table with varchar column
I'm not sure if a string of length n can be stored in varchar(n) column, please fix if not. This also checks that a string literal can start with a digit, so one shouldn't reuse identifier lexer pattern for that. If that's too evil, change the strings to "ab"/"abc"/"abcd".
Also: removed unused table_schema.