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.
Related
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
i have a doubt that how to get the result of the prepared statement query in android.Actually i have a need that i want the row id from database while comparing a field words which can contain ' or" so i want to use prepared statement ,after googling out i did not get any proper example for android sqlite database ,please tell me how to use the prepared statement in android and after running query ,how to use value either through result set or through cursor.below is query look like-
String perfect_stmnt="select ID from Annotation where HighlightedWord=? ";
try{
** Connection con=DriverManager.getConnection("file:/"+ db.getPath());**
pstmt = con.prepareStatement(perfect_stmnt);
pstmt.setString(1, highlightword);
Resultset rs = pstmt.executeQuery();
Here the major doubt i am having how to get the connection here see the line having **
Thanks
The Android database API can prepare a statement (see compileStatement), but it is not possible to get a cursor or result set from that.
You can use compiled statements only if they return a single value, or nothing.
Please note that SQLite does not have a large overhead when preparing statements, so you can just call query or rawQuery multiple times.
I have a weird problem that I need to solve, I have a Result Set in Java with data from one Oracle DB, and I need to insert this data into a DB 2 table. Both, the query and the DB2 Table has the same structure, but there's too many records (More than 200k) so make it with an iteration is too slow.
I want to do something like:
Connection DB2Connection = DriverManager.getConnection(Url,Usr,Pwd);
ResultSet rs_oracle = statement.executeQuery("Select * from ORACLE.table1");
ResultSet rs_db2 = statement2.executeQuery("Select * from DB2.table2")
/*PSEUDO*/
rs_db2 += rs_oracle;
DB2Connection.commit();
And insert all the records from the rs_oracle into the DB2 Table.
There's any way to do it without an iteration?
You could go for a prepared statement and do a batch insert on that.
I am trying to use some query result to generate another query and execute the new query but that does not seem to work. The second query is not being executed. Can someone please tell me why? This is that part of the code.
Statment stmt = connnection.createStatement();
Statment stmt2 = connnection.createStatement();
ResultSet r = stmt.executeQuery("Select * from employees");
while (r.next()) {
String Str = "Select name from employees where employeeId = " + (r.getInt(3) + 1);
System.out.println(str);
query = stmt2.executeQuery(str);
System.out.println(query.getString(1));}
The right query seems to be generated, but just won't execute. Is there a reason why this is so. BTW "query" is declared as resultset.
Thanks
you can only have one statement executing at one moment in time against one database connection -- so you can either open another database connection and execute the second statement in the 2nd connection, or iterate through the resultset from first statement and store the employees database id's (e.g. in an array/collection) then close that statement and run the second one, this time retrieving the id's from the array/collection you saved them in.
Following on from one of my previous questions to do with method design I was advised to implemented my SQL queries as a parameterized query as opposed to a simple string.
I've never used parameterized queries before so I decided to start with something simple, take the following Select statement:
String select = "SELECT * FROM ? ";
PreparedStatement ps = connection.prepareStatement(select);
ps.setString(1, "person");
This gives me the following error: "[SQLITE_ERROR] SQL error or missing database (near "?": syntax error)"
I then tried a modified version which has additional criteria;
String select = "SELECT id FROM person WHERE name = ? ";
PreparedStatement ps = connection.prepareStatement(select);
ps.setString(1, "Yui");
This version works fine, in the my first example am I missing the point of parameterized queries or am I constructing them incorrectly?
Thanks!
Simply put, SQL binds can't bind tables, only where clause values. There are some under-the-hood technical reasons for this related to "compiling" prepared SQL statements. In general, parameterized queries was designed to make SQL more secure by preventing SQL injection and it had a side benefit of making queries more "modular" as well but not to the extent of being able to dynamically set a table name (since it's assumed you already know what the table is going to be).
If you want all rows from PERSON table, here is what you should do:
String select = "SELECT * FROM person";
PreparedStatement ps = connection.prepareStatement(select);
Variable binding does not dynamically bind table names as others mentioned above.
If you have the table name coming in to your method as a variable, you may construct the whole query as below:
String select = "SELECT * FROM " + varTableName;
PreparedStatement ps = connection.prepareStatement(select);
Parameterized queries are for querying field names - not the table name!
Prepared statements are still SQL and need to be constructed with the appropriate where clause; i.e. where x = y. One of their advantages is they are parsed by the RDMS when first seen, rather than every time they are sent, which speeds up subsequent executions of the same query with different bind values.