Discord Java JDA | deleting data from SQLite / getting data from SQLite

I'm trying to make a ticket-based support system and I would like to know how to read and delete data from a SQLite table.

The system will work like this:
You click on a reaction and the bot checks if you already have a dedicated channel, if not it will create one.
If you close the ticket by clicking on a reaction in your personal channel, the channel and your data will be deleted.

That's my code so far:

public void onMessageReactionAdd(MessageReactionAddEvent event) {
		
		if(!event.getUser().isBot()) {
			if(event.getChannel().getIdLong() == 747412032281772033l && event.getReactionEmote().getEmoji().equals("\uD83C\uDFAB")) {
			
				ResultSet set = LiteSQL.onQuery("SELECT channelid FROM ticketchans WHERE guildid = " + event.getGuild().getIdLong() + " AND userid = " + event.getUserIdLong());
				
				try {
					Long user = set.getLong("userid");
					if(!(user == event.getUserIdLong())){
						
						Category cat = ((GuildChannel) event.getChannel()).getParent();
						TextChannel chan = cat.createTextChannel(event.getMember().getEffectiveName() + "'s TicketChannel").complete();
						
						EmbedBuilder builder = new EmbedBuilder();
						builder.setDescription("Hi " + event.getMember().getAsMention() + ", bitte beschreibe hier detailiert dein Anliegen. Wenn du dein ticket schliessen willst klicke auf das X");
		                builder.setColor(Color.decode("#910cc9"));
		                chan.sendMessage(builder.build()).queue(Message -> {
		                	Message.addReaction("\u274C").queue();
		                });
		                set.next();
		                LiteSQL.onUpdate("INSERT INTO ticketchans(guildid, channelid, userid) VALUES(" +
								event.getGuild().getIdLong() + ", " + event.getChannel().getIdLong() + ", " + event.getUserIdLong() + ")");
						
		                event.getChannel().sendMessage(event.getUser().getAsMention() + " TicketChannel eröffnet!").complete().delete().queueAfter(4, TimeUnit.SECONDS);
						
					}
				}catch (SQLException e) {}
			}
			
			if(event.getReactionEmote().getEmoji().equals("\u274C")) {
				
//delete data in table			event.getGuild().getGuildChannelById(event.getChannel().getIdLong()).delete().reason("").queue();
    
			}
}
}

Getting Data from SQLite

Most of this applies to SQL in general and isn't specific to SQLite.

First off, a SELECT statement consists of different parts.

SELECT columns FROM table WHERE condition;

For columns you have to fill in the names of the columns you want to get from your table. Pretty self-explanatory.
If you want to select more than one column, you just have to list them with commas, like this:

SELECT column1, column2, column3 FROM table WHERE condition;

In order to select every column of your table you just write * instead of the columns.

SELECT * FROM table WHERE condition;

Note: You can only access columns in your ResultSet if you selected them in your statement. If you select channelid you won't be able to get userid, unless you select it as well. (SELECT channelid, userid FROM table WHERE condition;)

You seem to understand the WHERE part so I will skip it. In case you need some more help or want to expand your usage of SQLite even more, you may check out some tutorials online.

Now, after writing your correct SELECT statement it's time to access the data in Java.

Therefore, you have to loop through your ResultSet.

ResultSet rs = LiteSQL.onQuery(
"SELECT channelid, userid
FROM ticketchans 
WHERE guildid = " + event.getGuild().getIdLong() + " 
AND userid = " + event.getUserIdLong()
);
// loop through the result set  
while (rs.next()) {  
Long userid = rs.getLong("userid");   
Long channelid = rs.getLong("channelid");   
}  

You now have the data you need and can use it for whatever you want.

Deleting Data from SQLite

Most of this applies to SQL in general and isn't specific to SQLite.

The DELETE statement has a similar structure to the SELECT statement although it lacks the columns (of course).

DELETE FROM table WHERE condition;

As explained in the first part, you have to choose the table you want to delete data from and then narrow it down using conditions.

In your case, deleting a specific ticket would be like this:

DELETE FROM ticketchans WHERE guildid = GID and userid = UID and channelid = CID;

If you don't use all three IDs in the condition, you might end up deleting all tickets of a guild or of an user. Since the channelid is always unique you could possibly skip the userid = UID part, but the details are up to you.

As already mentioned, if you want more specific statements or need some variations, check out a tutorial of your liking. (The one provided is just an example, use whatever you are comfortable with.)

On another note: I would advice not using .complete() but .queue() instead.
If you want to know why and how, check out this page.-Using-RestAction>)