ALTER TABLE ALTER COLUMN no longer copies the data for widening conversions (for…

ALTER TABLE ALTER COLUMN no longer copies the data for widening conversions (for example if only the precision was increased) unless necessary.

h2/src/main/org/h2/command/ddl/AlterTableAlterColumn.java

@@ -32,7 +32,6 @@ import org.h2.table.Column;
 import org.h2.table.Table;
 import org.h2.table.TableView;
 import org.h2.util.New;
-import org.h2.value.Value;
 
 /**
  * This class represents the statements
@@ -113,20 +112,14 @@ public class AlterTableAlterColumn extends SchemaCommand {
             break;
         }
         case CommandInterface.ALTER_TABLE_ALTER_COLUMN_CHANGE_TYPE: {
-            // If the change is only increasing the length of a VARCHAR type, then we don't need to copy the table
-            // because the length is only a constraint, and does not affect the storage structure.
-            if ((oldColumn.getType() == Value.STRING || oldColumn.getType() == Value.STRING_IGNORECASE)
-                && oldColumn.getPrecision() <= newColumn.getPrecision()
-                && oldColumn.isNullable() == newColumn.isNullable()
-                && oldColumn.isAutoIncrement() == newColumn.isAutoIncrement()
-                && oldColumn.isPrimaryKey() == newColumn.isPrimaryKey()
-                && oldColumn.getType() == newColumn.getType())
-            {
-                oldColumn.setPrecision(newColumn.getPrecision());
+            // if the change is only increasing the precision, then we don't
+            // need to copy the table because the length is only a constraint,
+            // and does not affect the storage structure.
+            if (oldColumn.isWideningConversion(newColumn)) {
+                convertAutoIncrementColumn(newColumn);
+                oldColumn.copy(newColumn);
                 db.update(session, table);
-            }
-            else
-            {
+            } else {
                 oldColumn.setSequence(null);
                 oldColumn.setDefaultExpression(session, null);
                 oldColumn.setConvertNullToDefault(false);

h2/src/main/org/h2/table/Column.java

@@ -63,8 +63,8 @@ public class Column {
 
     private final int type;
     private long precision;
-    private final int scale;
-    private final int displaySize;
+    private int scale;
+    private int displaySize;
     private Table table;
     private String name;
     private int columnId;
@@ -128,19 +128,7 @@ public class Column {
 
     public Column getClone() {
         Column newColumn = new Column(name, type, precision, scale, displaySize);
-        // table is not set
-        // columnId is not set
-        newColumn.nullable = nullable;
-        newColumn.defaultExpression = defaultExpression;
-        newColumn.originalSQL = originalSQL;
-        // autoIncrement, start, increment is not set
-        newColumn.convertNullToDefault = convertNullToDefault;
-        newColumn.sequence = sequence;
-        newColumn.comment = comment;
-        newColumn.computeTableFilter = computeTableFilter;
-        newColumn.isComputed = isComputed;
-        newColumn.selectivity = selectivity;
-        newColumn.primaryKey = primaryKey;
+        newColumn.copy(this);
         return newColumn;
     }
 
@@ -245,7 +233,7 @@ public class Column {
     public void setPrecision(long p) {
         precision = p;
     }
-    
+
     public int getDisplaySize() {
         return displaySize;
     }
@@ -658,4 +646,69 @@ public class Column {
         return name;
     }
 
+    /**
+     * Check whether the new column is of the same type and not more restricted
+     * than this column.
+     *
+     * @return true if the new column is compatible
+     */
+    public boolean isWideningConversion(Column newColumn) {
+        if (type != newColumn.type) {
+            return false;
+        }
+        if (precision > newColumn.precision) {
+            return false;
+        }
+        if (scale != newColumn.scale) {
+            return false;
+        }
+        if (nullable && !newColumn.nullable) {
+            return false;
+        }
+        if (convertNullToDefault != newColumn.convertNullToDefault) {
+            return false;
+        }
+        if (primaryKey != newColumn.primaryKey) {
+            return false;
+        }
+        if (autoIncrement || newColumn.autoIncrement) {
+            return false;
+        }
+        if (checkConstraint != null || newColumn.checkConstraint != null) {
+            return false;
+        }
+        if (convertNullToDefault || newColumn.convertNullToDefault) {
+            return false;
+        }
+        if (defaultExpression != null || newColumn.defaultExpression != null) {
+            return false;
+        }
+        if (isComputed || newColumn.isComputed) {
+            return false;
+        }
+        return true;
+    }
+
+    public void copy(Column newColumn) {
+        checkConstraint = newColumn.checkConstraint;
+        checkConstraintSQL = newColumn.checkConstraintSQL;
+        displaySize = newColumn.displaySize;
+        name = newColumn.name;
+        precision = newColumn.precision;
+        scale = newColumn.scale;
+        // table is not set
+        // columnId is not set
+        nullable = newColumn.nullable;
+        defaultExpression = newColumn.defaultExpression;
+        originalSQL = newColumn.originalSQL;
+        // autoIncrement, start, increment is not set
+        convertNullToDefault = newColumn.convertNullToDefault;
+        sequence = newColumn.sequence;
+        comment = newColumn.comment;
+        computeTableFilter = newColumn.computeTableFilter;
+        isComputed = newColumn.isComputed;
+        selectivity = newColumn.selectivity;
+        primaryKey = newColumn.primaryKey;
+    }
+
 }

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

@@ -143,4 +143,5 @@ public class TestAlter extends TestBase {
         stat.execute("insert into t values('Hello')");
         stat.execute("drop table t");
     }
+
 }