Various Notes on Project #1.


1. select ... from tab1 tab2 ...

   Looks at EVERY pair of rows, one from tab1 and one from tab2.  If 
   tab1 has N rows and tab2 has M, this is N x M pairs.

2. The pattern /\*.*\*/ (in String form "/\\*.*\\*/") matches too much.
   It matches ALL of 
       /* foo */ load bar ; /* baz */
   for example, rather than just the first comment.  You want to use
   .*? (the "reluctant quantifier") instead of .* (the "greedy quantifier").
   X* matches as many X's as it can, while X*? matches as few as it can
   get away with (and have the rest of the input match).  

3. I recommend against 

      inp.useDelimiter (";");

   to read entire commands.  Literals can contain ;'s, and this will
   cause confusion.   The project was designed to allow you to use
   just .next() and .hasNext()  with the default delimiters, with a 
   little special-casing for comments and literals.  So use .hasNext(patn)
   to detect when you have a comment or literal next, and otherwise just
   use .next ().  To get an entire command, then, you use do a bunch of
   .next()'s (special-casing the literals, since they can contain blanks),
   until you get a ";". 

   To read a literal once you see that it's coming up with 
   hasNext, people have either 
      1. Read the next token (which starts with "'"),
      2. If the that token does not contain the closing "'", then
         a. Change the delimiter to "'",
	 b. Read the next token,
	 c. Change the delimiter back.
	 d. Check that the token after that is a "'"
	 e. Concatenate the pieces into a literal.
    OR (easier)
      1. Use findWithinHorizon to match ' followed by any number of
         characters other than "'", ",", "\n", or "\r", followed by 
	 an optional "'" (optional for the case where the user left off
	 the closing "'").
   

4. You don't need to write "[\\s]"; plain "\\s" is equivalent.
   Likewise, you can just use ";" for "[;]", since ; is not a special
   character in patterns.

5. Beware: .startsWith, .endsWith, and .equals do NOT take patterns; they
   match literal strings.

6. A number of people have had this problem for the same reason:

     > When i run "gmake check" I do not pass any tests.
     > But, if I run "java db61b < testing/test1.in" I get the same output as
     > test1.out.

   The reason is that you have hard-wired in the directory "testing" in
   your load command.  You require that all database files ever used go
   into a directory called "testing", which is a bit odd.  To test things
   as 'gmake check' does,

   1. Change to the subdirectory testing (cd testing).

   2. Run Java with 

	 java -classpath .. db61b

   You can also use gjdb in the same way:

   1. Change to the subdirectory testing (cd testing) in your Emacs shell.

   2. Start gjdb from there, and when it prompts you with the 
      "Run gjdb (like this) " line, enter

          gjdb -classpath db61b

      instead of 

          gjdb db61b

7. The message

      Note: Some input files use unchecked or unsafe operations.
      Note: Recompile with -Xlint:unchecked for details.

    probably means that you wrote, e.g., ArrayList instead of 
    ArrayList<String>.  Change the line in your Makefile that
    reads

	javac -g $<

    to

        javac -g -Xlint:unchecked $<

    to see where you've made this error.