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Can retrieve one record from database but not another using JDBC

So, for a school project, I am building a discord bot. One of the features that I have built in is that he can retrieve gif links from a MySQL database, and send them in a message. Now, my issue is that I am only able to retrieve one record from my database, and no other records. If I put the query that I use into MySQL workbench and run it, it will retrieve those records.
This is the method for retrieving the gifs
public static ArrayList<Gif> GetGifsFromDB(String msg){
ArrayList<Gif> gifs = new ArrayList<>();
try(Connection conn = (Connection)DriverManager.getConnection(url, userName, password)){
Class.forName("com.mysql.jdbc.Driver").newInstance();
Statement stmnt = conn.createStatement();
String sql = "Select * from gif WHERE Type = '" + msg + "'";
stmnt.execute(sql);
try(ResultSet rs = stmnt.getResultSet()){
while(rs.next()){
Gif g = new Gif();
g.setID(rs.getInt("GifID"));
g.setURL(rs.getString("GifURL"));
System.out.println(g.getID() + g.getURL());
gifs.add(g);
}
rs.close();
conn.close();
}
}
catch(SQLException ex){
System.err.println(ex.getMessage());
}
catch(Exception ex){
System.err.println(ex.getMessage());
}
return gifs;
}
The "Type" in the database it just a category. With the test data I have in there, the 3 types are no, surprised and lonely. Only no returns a gif.

Remove closing ResultSet and Connection lines:
rs.close();
conn.close();
You are already closing it using try-with-resources

Issue ended up being with MySql not committing records to the database. Once workbench was refreshed, the added records disappeared. Rather strange that even though the records weren't in the database, they could be retrieve.

Most likely your msg is not exactly matching with any of the values for the database Type column.
Test by running
SELECT COUNT(*) FROM gif WHERE Type = '... put msg content here ...'
Do this manually directly on the database.
You can also try to put following line of code at the end:
System.out.println("Number of Selected Gifs: "+gifs.size());
If either of those results zero, then it means that msg was not exactly matched with Type. Maybe uppercase/lowercase issue?
Also to avoid SQL Injection, and other issues, please strongly consider using bind variables using a PreparedStatement.

How to query SQL Server CDC through JDBC incrementally

I am trying to incrementally read SQL Server CDC changes.
In my first interval, I query
Statement statement = connection.createStatement();
String queryString = "SELECT * FROM cdc.fn_cdc_get_all_changes_dbo_mytable(sys.fn_cdc_get_min_lsn('dbo_mytable'), " +
"sys.fn_cdc_get_max_lsn(), 'all') ORDER BY __$seqval";
ResultSet rs = statement.executeQuery(queryString);
Now I know that __$start_lsn is an LSN (Log Sequence Number) in binary(10). Although I don't understand how I can read it as a Java type so that I can include it my next query and how should I create my next query where I will like to specify the min_lsn as the last LSN which I processed.

You can use several options for retrieving the data from the ResultSet
Then for creating a new query, look at using a a PreparedStatement. There are several options for setting the data based on the type that you you pulled out of the initial query.

Java DB Database, check for all table names

I've got an embedded Derby Database in my java application, and have multiple table's (that are created and deleted, so nothing is set in stone). I wanted to be able to return a list of names of all the tables currently in the database as I have to display the list in the application as well as get all the information from them.
Easiest way to do so? I don't need code just a method or methods. I'm a terrible google-fu user.
Currently my code works by grabbing a ResultSet from a specific table name entered, but it's only for testing purposes and I need to be able to display the full list of tables I have.
EDIT: My current workaround is actually different than posted. I simply have another table that holds all the table names created and updates when one is created/deleted. Obviously not the best approach but it works for me right now.

DatabaseMetaData metaData = connection.getMetaData();
ResultSet resultSet = metaData.getTables(null, "schenaName", "%" ,new String[] {"TABLE"} );
while (resultSet.next()) {
System.out.println(resultSet.getString(3));
}
Adding new answer:
Connection connection = getDBConnection();
DatabaseMetaData dbMetaData = connection.getMetaData();
//getting catalogs for mysql DB, if it is not working for your DB, try dbMetaData.getSchemas();
ResultSet catalogs = dbMetaData.getCatalogs();
while(catalogs.next()){
String catalogName = catalogs.getString(1);
//excluding table names from "mysql" schema from mysql DB.
if(!"mysql".equalsIgnoreCase(catalogName)){
ResultSet tables = dbMetaData.getTables(catalogName, null, null, null);
while(tables.next()){
System.out.println(catalogName + "::"+tables.getString(3));
}
}
}

Using metadata is the (somewhat) more portable solution. Note that you don't need the catalog stuff with Derby, as there are no catalogs. You can issue dmd.getTables(...) directly with null for the catalog. If all the tables you track are in a single schema, (and there aren't any other tables in that schema), getTables(null, "schemaName", null, null) should do the trick.
If need more fancy querying and you're not concerned about portability, you can check out
the dataBaseMetaData tool which gives you access to metadata as tables so that you can perform joins and other sophisticated queries on them.

Try this:
select tableName from sys.systables
You should get all the tables your system.

Setting work_mem in Postgres for specific queries

I'm using a library that delegates to a JDBC driver for PostgreSQL, and some queries are very complex and require more memory. I don't want to set work_mem to something large for all queries, just this subset. The problem is that executing the following code results in an error:
// pseudo-code for what is happening
String sql = "set work_mem = 102400;";
sql += "SELECT * FROM expensive_query";
ResultSet rs = DatabaseDriver.execute(sql);
When I run this I get an error that:
set work_mem = 102400;
returns no results.
This works in pgAdmin because you can execute multiple queries at once. Is there a better way to do this or do I need to execute arbitrary SQL and then extract the result set I want?

I have no idea what DatabaseDriver does, but with "plain" JDBC you just need to do the following:
Statment stmt = connection.createStatement();
stmt.execute("set work_mem = 102400");
ResultSet rs = stmt.executeQuery("select ...");

Try to do that using Batch Processing

Which way is better for update database record?

I have two method for update:
String query = "update mytable set name = 'new_value' where id ='20' ";
Connection conn;
PreparedStatement pState;
try {
conn = DriverManager.getConnection(dbUrl, "root", "2323");
pState = conn.prepareStatement(query);
pState.executeUpdate();
} catch (SQLException sql) {
sql.printStackTrace();
}
OR:
String query = "update mytable set name = ?" + "where id = ?";
Connection conn;
PreparedStatement pState;
int s;
try {
conn = DriverManager.getConnection(dbUrl, "root", "2323");
pState = conn.prepareStatement(query);
pState.setStringt(1, "new_value");
pState.setString(2, "20");
s = pState.executeUpdate(); // if s = 1 then update done successfully
} catch (SQLException sql) {
sql.printStackTrace();
}
Both methods update database record correctly, Which is better?

Second approach is good practice to avoid SQL Injection attacks.
And following is enough to construct query String, another + concatenation is not required.
String query = "update mytable set name = ? where id = ?";

I would say the second approach.
You aren't returning anything, so why create a result set and go down that path?
Edit:
Even after your comment, I would still use the second template. It's more flexible. Additionally, it's faster. The PreparedStatement is pre-compiled in the database which allows the database to execute a parametric query using the statement faster than a normal query. This won't happen if you use string concatenation (like in your first example).
See: http://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html
Additionally, from that page:
The main feature of a PreparedStatement object is that, unlike a
Statement object, it is given a SQL statement when it is created. The
advantage to this is that in most cases, this SQL statement is sent to
the DBMS right away, where it is compiled. As a result, the
PreparedStatement object contains not just a SQL statement, but a SQL
statement that has been precompiled. This means that when the
PreparedStatement is executed, the DBMS can just run the
PreparedStatement SQL statement without having to compile it first.
Although PreparedStatement objects can be used for SQL statements with
no parameters, you probably use them most often for SQL statements
that take parameters. The advantage of using SQL statements that take
parameters is that you can use the same statement and supply it with
different values each time you execute it.

The second way is more faster if you use frequently the same query. Depends of the database vendor, the query is cached and the efficiency is higher than that using flat sentences. But all that depends on the implementation of the JDBC driver and the services provided by the database.
See more in Using Prepared Statements in the The Java Tutorials.