When I invoke following rows:
Statement statement = connection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY);
ResultSet resultSet = statement.executeQuery("select * from user");
resultSet.next();
resultSet.refreshRow();//exception throws here
I see following exception:
com.mysql.jdbc.NotUpdatable: Result Set not updatable.This result set
must come from a statement that was created with a result set type of
ResultSet.CONCUR_UPDATABLE, the query must select only one table, can
not use functions and must select all primary keys from that table.
See the JDBC 2.1 API Specification, section 5.6 for more details.This
result set must come from a statement that was created with a result
set type of ResultSet.CONCUR_UPDATABLE, the query must select only one
table, can not use functions and must select all primary keys from
that table. See the JDBC 2.1 API Specification, section 5.6 for more
details.
I wondered this exception because if read refreshRow method javadoc we can find following:
The refreshRow method provides a way for an application to explicitly
tell the JDBC driver to refetch a row(s) from the database
Thus following direction: database --> ResultSet
I have following understanding:
updatable is possibility to use following direction:
ResultSet --> database
Thus I don't understand cause of problem.
please clarify.
When you are using, ResultSet.CONCUR_READ_ONLY, you are getting an exception, that
com.mysql.jdbc.NotUpdatable: Result Set not updatable.This result set
must come from a statement that was created with a result set type of
ResultSet.CONCUR_UPDATABLE, the query must select only one table, can
not use functions and must select all primary keys from that table.
See the JDBC 2.1 API Specification, section 5.6 for more details.\
So, changing ResultSet.CONCUR_READ_ONLY to ResultSet.CONCUR_UPDATABLE, solved your problem. Correct?
Now, as I understand, you don't want to do that. Am I right? If yes, then I think you are confusing ResultSet with Database,
ResultSet.CONCUR_READ_ONLY, means read only ResultSet, not Database, similarly
ResultSet.CONCUR_UPDATABLE, means updatable ResultSet, not Database.
The method, resultSet.refreshRow(), suppose to update the resultSet, hence it rightly requires updatable ResultSet. I hope it's clear now.
Related
I want to fetch Column comments using JDBC Metadata , But everytime it returns null , I tested with Oracle and SqlServer both cases it returning Null.
DatabaseMetaData dmt = con.getMetaData();
colRs = dmt.getColumns(null, "dbo", 'Student', null);
while (colRs.next()) {
System.out.println(colRs.getString("REMARKS");
}
While i am getting all other data like column name , length etc absolutely ok ...
For Oracle you need to provide a connection property remarksReporting and set that to true or call the method setRemarksReporting() to enable that.
OracleConnection oraCon = (OracleConnection)con;
oraCon.setRemarksReporting(true);
After that, getColumns() will return the column (or table) comments in the REMARKS column of the ResultSet.
See Oracle's JDBC Reference for more details
For SQL Server this is not possible at all.
Neither the Microsoft nor the jTDS driver expose table or column comments. Probably because there is no SQL support for that in SQL Server. The usual approach of using "extended properties" and the property name MS_DESCRIPTION is not reliable. Mainly because there is no requirement to us MS_DESCRIPTION as the property name. Not even sp_help returns those remarks. And at least the jTDS driver simply calls sp_help go the the table columns. I don't know what the Microsoft driver does.
The only option you have there, is to use fn_listextendedproperty() to retrieve the comments:
e.g.:
SELECT objname, cast(value as varchar(8000)) as value
FROM fn_listextendedproperty ('MS_DESCRIPTION','schema', 'dbo', 'table', 'Student', 'column', null)
You need to replace MS_DESCRIPTION with whatever property name you use to store your comments.
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.
I want to INSERT several rows using a PreparedStatement:
ps = con.prepareStatement(query,PreparedStatement.RETURN_GENERATED_KEYS);
for(Element e:listOfElements){
ps.setString(1,this.col_val_1);
ps.setString(2,this.col_val_2);
ps.setInt(3,this.col_val_3);
ps.addBatch();
}
ps.executeBatch();
ResultSet rs = ps.getGeneratedKeys();
At this point, whent I expect to get the PK's generated for each INSERT, I get this SQLServerException:
com.microsoft.sqlserver.jdbc.SQLServerException: The statement must be executed before any results can be obtained.
I expected to get a ResultSet with one row for each insert performed, so I could get each PK generated.
Am I expecting wrong? Am I doing something wrong? Can it be done in a different way using batch execution?
Support for getGeneratedKeys() on batch execution is implementation defined according to the JDBC spec. Most likely the SQL Server driver does not support it for batch execution.
I tried to look for an explicit statement on the Microsoft site, but couldn't find it. This old (2007) forum post on MSDN does state that it isn't supported: http://social.msdn.microsoft.com/Forums/en-US/sqldataaccess/thread/6cbf5eea-e5b9-4519-8e86-f4b65ce3f8e1
String link = "http://hosted.ap.org";
I want to find whether the given url is already existing in the SQL DB under the table name "urls". If the given url is not found in that table i need to insert it in to that table.
As I am a beginner in Java, I cannot really reach the exact code.
Please advise on this regard on how to search the url in the table.
I am done with the SQL Connection using the java code. Please advise me on the searching and inserting part alone as explained above.
PreparedStatement insert = connectin.preparedStateme("insert into urls(url) vlaues(?)");
PreparedStatement search = connectin.preparedStateme("select * from urls where url = ?");
search.setString(1, <your url value to search>);
ResultSet rs = search.executeQuery();
if (!rs.hasNext()) {
insert.setString(1, <your url value to insert>);
insert.executeUpdate();
}
//finally close your statements and connection
...
i assumed that you only have one field your table and field name is url. if you have more fields you need to add them in insert query.
You need to distinguish between two completely separate things: SQL (Structured Query Language) is the language which you use to communicate with the DB. JDBC (Java DataBase Connectivity) is a Java API which enables you to execute SQL language using Java code.
To get data from DB, you usually use the SQL SELECT statement. To insert data in a DB, you usually use the SQL INSERT INTO statement
To prepare a SQL statement in Java, you usually use Connection#prepareStatement(). To execute a SQL SELECT statement in Java, you should use PreparedStatement#executeQuery(). It returns a ResultSet with the query results. To execute a SQL INSERT statement in Java, you should use PreparedStatement#executeUpdate().
See also:
SQL tutorial
JDBC tutorial
I'm busy on a piece of code to get alle the column names of a table from an Oracle database. The code I came up with looks like this:
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());
Connection conn = DriverManager.getConnection(
"jdbc:oracle:thin:#<server>:1521:<sid>", <username>, <password>);
DatabaseMetaData meta = conn.getMetaData();
ResultSet columns = meta.getColumns(null, null, "EMPLOYEES", null);
int i = 1;
while (columns.next())
{
System.out.printf("%d: %s (%d)\n", i++, columns.getString("COLUMN_NAME"),
columns.getInt("ORDINAL_POSITION"));
}
When I ran this code to my surprise too many columns were returned. A closer look revealed that the ResultSet contained a duplicate set of all the columns, i.e. every column was returned twice. Here's the output I got:
1: ID (1)
2: NAME (2)
3: CITY (3)
4: ID (1)
5: NAME (2)
6: CITY (3)
When I look at the table using Oracle SQL Developer it shows that the table only has three columns (ID, NAME, CITY). I've tried this code against several different tables in my database and some work just fine, while others exhibit this weird behaviour.
Could there be a bug in the Oracle JDBC driver? Or am I doing something wrong here?
Update: Thanks to Kenster I now have an alternative way to retrieve the column names. You can get them from a ResultSet, like this:
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:#<server>:1521:<sid>", <username>, <password>);
Statement st = conn.createStatement();
ResultSet rset = st.executeQuery("SELECT * FROM \"EMPLOYEES\"");
ResultSetMetaData md = rset.getMetaData();
for (int i=1; i<=md.getColumnCount(); i++)
{
System.out.println(md.getColumnLabel(i));
}
This seems to work just fine and no duplicates are returned! And for those who wonder: according to this blog you should use getColumnLabel() instead of getColumnName().
In oracle, Connection.getMetaData() returns meta-data for the entire database, not just the schema you happen to be connected to. So when you supply null as the first two arguments to meta.getColumns(), you're not filtering the results for just your schema.
You need to supply the name of the Oracle schema to one of the first two parameters of meta.getColumns(), probably the second one, e.g.
meta.getColumns(null, "myuser", "EMPLOYEES", null);
It's a bit irritating having to do this, but that's the way the Oracle folks chose to implement their JDBC driver.
This doesn't directly answer your question, but another approach is to execute the query:
select * from tablename where 1 = 0
This will return a ResultSet, even though it doesn't select any rows. The result set metadata will match the table that you selected from. Depending on what you're doing, this can be more convenient. tablename can be anything that you can select on--you don't have to get the case correct or worry about what schema it's in.
In the update to your question I noticed that you missed one key part of Kenster's answer. He specified a 'where' clause of 'where 1 = 0', which you don't have. This is important because if you leave it off, then oracle will try and return the ENTIRE table. And if you don't pull all of the records over, oracle will hold unto them, waiting for you to page through them. Adding that where clause still gives you the metadata, but without any of the overhead.
Also, I personally use 'where rownum < 1', since oracle knows immediately that all rownums are past that, and I'm not sure if it's smart enough to not try and test each record for '1 = 0'.
In addition to skaffman's answer -
use the following query in Oracle:
select sys_context( 'userenv', 'current_schema' ) from dual;
to access your current schema name if you are restricted to do so in Java.
This is the behavior mandated by the JDBC API - passing nulls as first and second parameter to getColumns means that neither catalog name nor schema name are used to narrow the search.
Link to the documentation . It is true that some other JDBC drivers have different behavior by default (e.g MySQL's ConnectorJ by default restricts to the current catalog), but this is not standard, and documented as such