MySQL Connector/J 5.1 Developer Guide
Before version 3.0 of the JDBC API, there was no standard way of
retrieving key values from databases that supported auto
increment or identity columns. With older JDBC drivers for
MySQL, you could always use a MySQL-specific method on the
Statement
interface, or issue the query
SELECT LAST_INSERT_ID()
after issuing an
INSERT
to a table that had an
AUTO_INCREMENT
key. Using the MySQL-specific
method call isn't portable, and issuing a
SELECT
to get the
AUTO_INCREMENT
key's value requires another
round-trip to the database, which isn't as efficient as
possible. The following code snippets demonstrate the three
different ways to retrieve AUTO_INCREMENT
values. First, we demonstrate the use of the new JDBC 3.0 method
getGeneratedKeys()
which is now the
preferred method to use if you need to retrieve
AUTO_INCREMENT
keys and have access to JDBC
3.0. The second example shows how you can retrieve the same
value using a standard SELECT
LAST_INSERT_ID()
query. The final example shows how
updatable result sets can retrieve the
AUTO_INCREMENT
value when using the
insertRow()
method.
Example 6.8 Connector/J: Retrieving AUTO_INCREMENT
column values
using Statement.getGeneratedKeys()
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets assuming you have a // Connection 'conn' to a MySQL database already // available stmt = conn.createStatement(); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field // stmt.executeUpdate( "INSERT INTO autoIncTutorial (dataField) " + "values ('Can I Get the Auto Increment Field?')", Statement.RETURN_GENERATED_KEYS); // // Example of using Statement.getGeneratedKeys() // to retrieve the value of an auto-increment // value // int autoIncKeyFromApi = -1; rs = stmt.getGeneratedKeys(); if (rs.next()) { autoIncKeyFromApi = rs.getInt(1); } else { // throw an exception from here } System.out.println("Key returned from getGeneratedKeys():" + autoIncKeyFromApi); } finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } } }
Example 6.9 Connector/J: Retrieving AUTO_INCREMENT
column values
using SELECT LAST_INSERT_ID()
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets. stmt = conn.createStatement(); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field // stmt.executeUpdate( "INSERT INTO autoIncTutorial (dataField) " + "values ('Can I Get the Auto Increment Field?')"); // // Use the MySQL LAST_INSERT_ID() // function to do the same thing as getGeneratedKeys() // int autoIncKeyFromFunc = -1; rs = stmt.executeQuery("SELECT LAST_INSERT_ID()"); if (rs.next()) { autoIncKeyFromFunc = rs.getInt(1); } else { // throw an exception from here } System.out.println("Key returned from " + "'SELECT LAST_INSERT_ID()': " + autoIncKeyFromFunc); } finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } } }
Example 6.10 Connector/J: Retrieving AUTO_INCREMENT
column values
in Updatable ResultSets
Statement stmt = null; ResultSet rs = null; try { // // Create a Statement instance that we can use for // 'normal' result sets as well as an 'updatable' // one, assuming you have a Connection 'conn' to // a MySQL database already available // stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_UPDATABLE); // // Issue the DDL queries for the table for this example // stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate( "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"); // // Example of retrieving an AUTO INCREMENT key // from an updatable result set // rs = stmt.executeQuery("SELECT priKey, dataField " + "FROM autoIncTutorial"); rs.moveToInsertRow(); rs.updateString("dataField", "AUTO INCREMENT here?"); rs.insertRow(); // // the driver adds rows at the end // rs.last(); // // We should now be on the row we just inserted // int autoIncKeyFromRS = rs.getInt("priKey"); System.out.println("Key returned for inserted row: " + autoIncKeyFromRS); } finally { if (rs != null) { try { rs.close(); } catch (SQLException ex) { // ignore } } if (stmt != null) { try { stmt.close(); } catch (SQLException ex) { // ignore } } }
Running the preceding example code should produce the following output:
Key returned from getGeneratedKeys(): 1 Key returned from SELECT LAST_INSERT_ID(): 1 Key returned for inserted row: 1
At times, it can be tricky to use the SELECT
LAST_INSERT_ID()
query, as that function's value is
scoped to a connection. So, if some other query happens on the
same connection, the value is overwritten. On the other hand,
the getGeneratedKeys()
method is scoped by
the Statement
instance, so it can be used
even if other queries happen on the same connection, but not on
the same Statement
instance.