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ExecuteQuery() vs getResultSet() in Java

What is the difference between statement.executeQuery and statement.getResultSet(). I believe both will return ResultSet for a select statement but are there any specific criteria when we should use which of them.

In general you should use executeQuery if you know you are executing a select statement. The getResultSet() method by itself does not execute the statement.
The getResultSet is intended to be used in combination with execute. The execute methods are intended for use with unknown statement types, or statements that can produce multiple results (that is 0 or more update counts or result sets).
So in short: you should normally use executeQuery.
A simple example when you should use execute if the code doesn't know what query it is going to execute (an update, a query, or something more complex), for example when executing user provided queries.
Another example are SQL Server stored procedures, which can return multiple update counts and result sets.
A generic way of processing a result of execute is:
boolean isResultSet = statement.execute(sql);
while (true) {
if (isResultSet) {
try (ResultSet rs = statement.getResultSet()) {
// do something with result set
}
} else {
int updateCount = statement.getUpdateCount();
if (updateCount == -1) {
// -1 signals no more results
break;
}
// do something with update count
}
// move to next result
isResultSet = statement.getMoreResults();
}
This ensures that all* results get processed.
*: This example ignores exception results for systems (like SQL Server) that allow multiple exceptions to be interleaved with result sets and update counts, see How to get *everything* back from a stored procedure using JDBC for a more thorough example

Check out the JavaDoc for these methods. getResultSet can return null but executeQuery never return null.
There are also more constraints. For example executeQuery cannot be called on a PreparedStatement or CallableStatement.

parameterized insert/update in sql

I am trying to insert into a db that I have, and I'd like to do so through parameters. I am connecting to a postgres db using java.
I can connect to the db just fine. I know that because I have various operations that I am using that are already working were I can see, and update existing rows in my db. I am having trouble with INSERT.
I have the following:
private String _update_rentals = "INSERT into rentals (cid, mid) values (?,?)";
private PreparedStatement _update_rentals_statement;
private String _update_movie_status = "UPDATE Movie SET checkedout = true WHERE mid = ?";
private PreparedStatement _update_movie_status_statement;
And I initialize them:
_update_movie_status_statement = _customer_db.prepareStatement(_update_movie_status);
_update_rentals_statement = _customer_db.prepareStatement(_update_rentals);
And
while (movieAvail.next()){
System.out.println(movieAvail.getBoolean(1));
if (movieAvail.getBoolean(1) == false){
//Do chekcout
_update_rentals_statement.clearParameters();
_update_rentals_statement.setInt(1, cid);
_update_rentals_statement.setInt(2, mid);
_update_rentals_statement.executeQuery();
_update_movie_status_statement.clearParameters();
_update_movie_status_statement.setInt(1, mid);
_update_movie_status_statement.executeQuery();
System.out.println("Enjoy your movie!");
}
}
I am getting an error with both of the executeQuery() calls. For some reason I am getting the following error with both:
Exception in thread "main" org.postgresql.util.PSQLException: No results were returned by the query.
I looked at other posts, and I believed that I was following syntax for both insert/ update correctly, so maybe I am overlooking some aspect of this.
This is all part of a larger code base, so I did not want to include the methods these pieces of code are in. But these are the isolated instances which play a part with this code.

In general, when you execute a query, you are willing to retrieve some kind of information from the database. This is usually the case when you are executing SELECT queries. However, with INSERT and UPDATE statements, you are not querying the database, you are simply executing an update or inserting new rows. In the documentation of PreparedStatement you can see in which cases an exception is being thrown when you try to call executeQuery:
Throws: SQLException - if a database access error occurs; this method
is called on a closed PreparedStatement or the SQL statement does not
return a ResultSet object
So in your case the problem is that your statements do not return a ResultSet. You should use execute or executeUpdate instead. The former simply executes the update, while the latter does the same, but also returns the number of affected rows.

I think the main issue is that you are calling executeQuery(), which expects a result to be returned, but Insert/Update are not queries and don't return a result. Try just calling execute().

java call oracle procedure with %rowtype parameter

I have been given an oracle procedure with the in out parameter %rowtype,like:
CREATE OR REPLACE PROCEDURE cleansing(
io_user IN OUT USER%rowtype
)
IS
BEGIN
--some pl/sql code
END cleansing;
USER is a table with more than 100 columns, I want to call the procedure by Java.
I can't change the procedure, because they are already used by other project.
I can't add procedure to database, because I don't have the permission to do it.
I google it, but can't find a good way to handle this.
what I want to do is:
1. pass the parameter.
2. get the parameter. some java demo code:
String sql = "{call cleansing(?)}";
try {
dbConnection = getDBConnection();
callableStatement = dbConnection.prepareCall(sql);
callableStatement.setXXX()//I don't know
callableStatement.registerOUTParameter(1, //I don't know the type.);
can anyone help me and give some demo code? no change to database and in out parameter mapping with java

This is possible but it's not really straightforward. You have to create something of type USER%ROWTYPE at runtime and use that to call your stored procedure. Take a look here for details.
To get output values as well, you have to do something extra, along the line of Sumit's comment. Basically, after your procedure call, you open a cursor that selects the relevant data from the USER parameter.
So you get a database statement as follows (pseudocode):
string sql =
"declare
user_param user%rowtype;
begin
-- Set necessary parameters
user_param.col0 := :p0In;
user_param.col1 := :p1In;
...
-- Call procedure.
cleansing(io_user => user_param);
-- Read necessary output values into cursor.
open :pOut for select user_param.col99 as col99
user_param.col98 as col98
...
from dual;
end;"
You call this entire statement the usual way, but you register a cursor out parameter (unfortunately, Java is a very long time ago for me so I'm not sure on the exact syntax).
callableStatement.registerOutParameter("pOut", OracleTypes.CURSOR);
...
callableStatement.execute();
...
ResultSet rs = (ResultSet) callableStatement.getObject("pOut");
// Read from result set.
EDIT: I turned this into a blogpost. Code examples are in C# but the idea is the same.

infinite loop "hangs" after some iterations in java code during mysql query

I have a long piece of code in java which uses selenium webdriver and firefox to test my website. Pardon me if I can't reproduce it here. It has an infinite while loop to keep doing its function repeatedly. Thats what its supposed to do. Also, I don't use multi threading.
Sometimes, it gets stuck. I use a windows system and the code runs on command prompt. When it gets stuck, no errors or exceptions are thrown. Its something like "it hangs" (only the window in which the code runs hangs). Then I have to use CTRL + C . Sometimes it resumes working after that, other times it gets terminated and I restart it. It works fine but after some loops it "hangs" again. Also, I've noticed that its usually during the execution of one of the methods querying mysql database.
The code runs an infinite loop. Each time, it queries the mysql database, fetches a value(whose 'status' field is not 'done') from a particular table (one value in each loop) and proceeds with testing with this value.At the end of the loop, the table is updated (the column 'status' is set to 'done' for that value). When there are no new values having 'status' not equal to 'done' in that particular table, it should ideally display "NO NEW VALUE". However, after all the values have been used, it simply takes up the last used value (even though its status is updated to 'done' at the end of previous loop) and goes ahead. I then have to terminate the execution and run the code again. This time when the infinite loop begins, it queries the database and correctly displays "NO NEW VALUE", queries again, displays the message again and so on(which is what it should do)
I close the sql connection using con.close().
It appears that after running the loop for a few times, some resource is getting exhausted somewhere. But this is only a wild guess.
Can anyone suggest what the problem is and how do I fix it ?
Below is a relevant piece of code :
try{
String sql = "select something from somewhere where id = ? and is_deleted = '0';";
System.out.println("\n"+sql + "\n? = " + pID);
PreparedStatement selQuery1 = conn.prepareStatement(sql);
selQuery1.setString(1, pID);
ResultSet rs1 = selQuery1.executeQuery();
//Extract data from result set
while(rs1.next() && i1<6){
//do something
}//end while loop
String sql2 = "select something2 from somewhere2 where id = ? and is_deleted = '0';";
System.out.println("\n"+sql2 + "\n? = " + pjID);
PreparedStatement selQuery2 = conn.prepareStatement(sql2);
selQuery2.setString(1, pjID);
ResultSet rs2 = selQuery2.executeQuery();
//Extract data from result set
while(rs2.next() && i1<6){
//do something
}//end while loop
System.out.println("\nDone.");
conn.close();
}catch (SQLException e) {
flag=false;
}
Please note that no exceptions are thrown anywhere. The window in which the code is running just freezes (that too once in while) after displaying both the query statements.

I forgot to close the query and the resultset. Just closing the connection should implicitly close the query and resultset but it doesn't work always.

I also faced the same problem recently. But in my case the issue was with indexes. I am just pointing out here so that it can be helpful to other folks.
In my case I am fetching the menu items from MenuMaster table from database. So after successfully log in, I am hitting a database to fetch the menu items using MySQL connector driver. Here I need to fetch parent menu with their child menus. In my query, in where clause I have not used any primary key or Unique key. So, it was taking a long time. So just make an index of that key, and it worked as charm...

How can I execute non-query Stored Procedure in JDBC

I have a stored procedure in a postgres database. I'm using the postgres JDBC driver to execute a stored procedure, and I do not care about the return type, and can't execute the query. It's indicating that there's a syntax error near the name of the function.
In procedures that return rows, I've been able to do this via a PreparedStatement and setting the parameters, like:
PreparedStatement prepared = connection.prepareStatement("SELECT * FROM NonQueryProcedure(?)");
prepared.setInt(1, 999);
// ....
ResulSet resultSet = prepared.executeQuery();
However, I can't seem to get this to work for an "update" stored procedure where I don't care about the return type. I've tried using connection.prepareStatement() and prepareCall(), and also tried executing it with statement.execute(), .executeUpdate(), and .executeQuery(), without success.
How can I execute a stored procedure where I don't care about the return type?

As PostgreSQL has no "real" procedures, functions are simply executed using a SELECT statement:
statement.execute("select NonQueryProcedure(?)");
Note that inside a PL/pgSQL function, you can use the perform statement to call such a function. But this is not available outside of a PL/pgSQL block.

Without the actual syntax error, I can't say for sure, but try this:
"SELECT * FROM \"getData\"(?)"
CamelCase/PascalCase is a BAD idea in any SQL database. Either it folds it to a single case and all you see is AMASSOFUNREADABLELETTERS or it requires quoting and you will have to forevermore type "aMassofLettersAndQuotesAndShiftKeysAndMyFingersHurt" anytime you want to avoid a syntax error.