SQL as script interpreter

[lvca]

We already have the OCommandScript class that execute a script at the server side. Now we could use this feature to specify "SQL" as scripting language with few, simple and powerful features taken from issue #2056.

If you execute a OCommandScript request passing SQL as language, all the SQL is supported and these commands more:

• begin -> begins a transaction
• rollback -> rollbacks an active transaction
• commit -> commits an active transaction
• let = -> executes a command and assign it in the context as . That variable can be used in further commands by prefixing it with $
• return -> returns the variable result instead of last command result
  Example:

    database.open("admin", "admin");

    String cmd = "";
    cmd += "begin";
    cmd += "\nlet a = create vertex set script = true";
    cmd += "\nlet b = select from v limit 1";
    cmd += "\ncreate edge from $a to $b retry 100";
    cmd += "\ncommit";
    cmd += "\nreturn $a";

    Object result = database.command(new OCommandScript("sql", cmd)).execute();

This is very useful to manipulate the graph at the server side with just one network call.