高健 wrote: > I have one question about prepared statement. > I use Java via JDBC, then send prepared statement to execute. > I thought that the pg_prepared_statments view will have one record after my execution. > But I can't find. > > Is the JDBC's prepared statement differ from SQL execute by prepare command ? > http://www.postgresql.org/docs/current/static/sql-prepare.html > > My simple java program is the following: > > import java.sql.*; > > public class Test01 { > public static void main(String argsv[]){ > try > { > Class.forName("org.postgresql.Driver").newInstance(); > String url = "jdbc:postgresql://localhost:5432/postgres" ; > Connection con = DriverManager.getConnection(url,"postgres","postgres" ); > ///Phase 1:-------------Select data from table----------------------- > System.out.println("Phase 1------------------------start"); > String strsql = " select * from customers where cust_id = ?"; > PreparedStatement pst=con.prepareStatement(strsql); > pst.setInt(1,3); //find the customer with cust_id of 3. > ResultSet rs = pst.executeQuery(); > while (rs.next()) > { > System.out.print("cust_id:"+rs.getInt( "cust_id")); > System.out.println("...cust_name:"+rs.getString( "cust_name" )); > } > > System.out.println("Phase 1------------------------end\n"); > > > > ///Phase 2:-------------Use connection again,to select data from data dictionary----------- > ------------ > System.out.println("Phase 2------------------------start"); > strsql = "select * from pg_prepared_statements"; > pst=con.prepareStatement(strsql); > rs = pst.executeQuery(); > while (rs.next()) > { > System.out.println("statement:"+rs.getString( "statement")); > } > System.out.println("Phase 2------------------------end\n"); > > > > ///Phase 3:-------------Use connection again,to select data from table--------------------- > -- > System.out.println("Phase 3------------------------start"); > strsql = "select * from customers"; > pst=con.prepareStatement(strsql); > rs = pst.executeQuery(); > while (rs.next()) > { > System.out.print("cust_id:"+rs.getInt( "cust_id")); > System.out.println("...cust_name:"+rs.getString( "cust_name" )); > } > System.out.println("Phase 3------------------------end\n"); > rs.close(); > pst.close(); > con.close(); > } > catch (Exception ee) > { > System.out.print(ee.getMessage()); > } > } > } > > > > The result of it's execution is: > > Phase 1------------------------start > > cust_id:3...cust_name:Taylor > > Phase 1------------------------end > > > > Phase 2------------------------start > > Phase 2------------------------end > > > > Phase 3------------------------start > > cust_id:1...cust_name:Smith > > cust_id:2...cust_name:Brown > > cust_id:3...cust_name:Taylor > > Phase 3------------------------end > > > > That is to say: my prepared statement is not cached by PG? > > Then how to write a java program to made it's prepared statement realized by PG to treat it as a > "prepared statement"? > > Thank you. See http://jdbc.postgresql.org/documentation/head/server-prepare.html Set the prepare threshold of a PreparedStatement and use the statement at least as many times. Then you should see an entry in pg_prepared_statements. In your example, no PreparedStatement is used more than once. Yours, Laurenz Albe -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
