Execute multiple SQL statements in java

Question

I want to execute a query in Java.

I create a connection. Then I want to execute an INSERT statement, when done, the connection is closed but I wan

Answer 1

In the abscence of the schema or the data contained in each table I'm going to make the following assumptions:

The table special_columns could look like this:

column_name
-----------
column_1
column_2
column_3

The table alldata2 could look like this:

column_1  | column_2  | column_3
---------------------------------
value_1_1 | value_2_1 | value_3_1
value_1_2 | value_2_2 | value_3_2    

The table alldata should, after inserts have, happened look like this:

colname
---------
value_1_1
value_1_2
value_2_1
value_2_2
value_3_1
value_3_2

Given these assumptions you can copy the data like this:

try (
  Connection connection = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl1", "test", "oracle")
)
{
  StringBuilder columnNames = new StringBuilder();

  try (
    Statement select = connection.createStatement();
    ResultSet specialColumns = select.executeQuery("SELECT column_name FROM special_columns");
    Statement insert = connection.createStatement()
  )
  {
    while (specialColumns.next())
    {
      int batchSize = 0;             

      insert.addBatch("INSERT INTO alldata(colname) SELECT " + specialColumns.getString(1) + " FROM alldata2"); 

      if (batchSize >= MAX_BATCH_SIZE)
      { 
        insert.executeBatch();
        batchSize = 0;
      }
    }

    insert.executeBatch();
  }

A couple of things to note:

• MAX_BATCH_SIZE should be set to a value based on your database configuration and the data being inserted.
• this code is using the Java 7 try-with-resources feature to ensure the database resources are released when they're finished with.
• you haven't needed to do a Class.forName since the service provider mechanism was introduced as detailed in the JavaDoc for DriverManager.