Fix for "Change not-null / null -constraint to existing column"

(MySql/ORACLE - SQL style)

Command failed silently corrupting the changed column.
Before the change (added after v1.4.196) following was observed:
 alter table T modify C int null; -- Worked as expected
 alter table T modify C null;     -- Silently corrupted column C

h2/src/docsrc/html/changelog.html

@@ -21,6 +21,8 @@ Change Log
 
 <h2>Next Version (unreleased)</h2>
 <ul>
+<li>Fix bug in MySQL/ORACLE-syntax silently corrupting the modified column in cases of setting the 'NULL'- or 'NOT NULL'-constraint. E.g. alter table T modify C NULL;
+</li>
 <li>Issue #570: MySQL compatibility for ALTER TABLE .. DROP INDEX
 </li>
 <li>Issue #537: Include the COLUMN name in message "Numeric value out of range"

h2/src/docsrc/html/history.html

@@ -166,6 +166,7 @@ To become a donor, use PayPal (at the very bottom of the main web page).
 </li><li>Cristan Meijer, Netherlands
 </li><li>Adam McMahon, USA
 </li><li>F&aacute;bio Gomes Lisboa Gomes, Brasil
+</li><li><a href="http://tao.works">Sam Blume, Switzerland</a>
 </li></ul>
 
 <!-- [close] { --></div></td></tr></table><!-- } --><!-- analytics --></body></html>

h2/src/docsrc/html/roadmap.html

@@ -344,7 +344,6 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 </li><li>Allow to scan index backwards starting with a value (to better support ORDER BY DESC).
 </li><li>Java Service Wrapper: try http://yajsw.sourceforge.net/
 </li><li>Batch parameter for INSERT, UPDATE, and DELETE, and commit after each batch. See also MySQL DELETE.
-</li><li>MySQL compatibility: support ALTER TABLE .. MODIFY COLUMN.
 </li><li>Use a lazy and auto-close input stream (open resource when reading, close on eof).
 </li><li>Connection pool: 'reset session' command (delete temp tables, rollback, auto-commit true).
 </li><li>Improve SQL documentation, see http://www.w3schools.com/sql/

h2/src/main/org/h2/command/Parser.java

@@ -5869,7 +5869,23 @@ public class Parser {
             // MySQL compatibility
             readIf("COLUMN");
             String columnName = readColumnIdentifier();
-            return parseAlterTableAlterColumnType(schema, tableName, columnName, ifTableExists);
+            if ((isToken("NOT") || isToken("NULL"))) {
+            	AlterTableAlterColumn command = new AlterTableAlterColumn(
+            			session, schema);
+            	command.setTableName(tableName);
+            	command.setIfTableExists(ifTableExists);
+            	Column column = columnIfTableExists(schema, tableName, columnName, ifTableExists);
+            	command.setOldColumn(column);
+                if (readIf("NOT")) {
+                    command.setType(CommandInterface.ALTER_TABLE_ALTER_COLUMN_NOT_NULL);
+                } else {
+                	read("NULL");
+                    command.setType(CommandInterface.ALTER_TABLE_ALTER_COLUMN_NULL);
+                }
+                return command;
+            } else {
+                return parseAlterTableAlterColumnType(schema, tableName, columnName, ifTableExists);
+            }
         } else if (readIf("ALTER")) {
             readIf("COLUMN");
             String columnName = readColumnIdentifier();

h2/src/test/org/h2/test/db/TestAlter.java

@@ -51,6 +51,7 @@ public class TestAlter extends TestBase {
         testAlterTableAddMultipleColumnsBefore();
         testAlterTableAddMultipleColumnsAfter();
         testAlterTableModifyColumn();
+        testAlterTableModifyColumnSetNull();
         conn.close();
         deleteDb(getTestName());
     }
@@ -283,4 +284,27 @@ public class TestAlter extends TestBase {
         stat.execute("insert into t values('Hello')");
         stat.execute("drop table t");
     }
+    
+    /**
+     * Test for fix "Change not-null / null -constraint to existing column" 
+     * (MySql/ORACLE - SQL style) that failed silently corrupting the changed 
+     * column.<br/>
+     * Before the change (added after v1.4.196) following was observed:
+     * <pre>
+     *  alter table T modify C int null; -- Worked as expected
+     *  alter table T modify C null;     -- Silently corrupted column C
+     * </pre>
+     */
+    private void testAlterTableModifyColumnSetNull() throws SQLException {
+        // This worked in v1.4.196
+        stat.execute("create table T (C varchar not null)");
+        stat.execute("alter table T modify C int null");
+        stat.execute("insert into T values(null)");
+        stat.execute("drop table T");
+        // This failed in v1.4.196 
+        stat.execute("create table T (C int not null)");
+        stat.execute("alter table T modify C null"); // Silently corrupted column C
+        stat.execute("insert into T values(null)"); // <- ERROR: NULL not allowed
+        stat.execute("drop table T");
+    }
 }