@Override public int update() { session.commit(true); Database db = session.getDatabase(); session.getUser().checkRight(table, Right.ALL); table.checkSupportAlter(); table.lock(session, true, true); Sequence sequence = oldColumn == null ? null : oldColumn.getSequence(); if (newColumn != null) { checkDefaultReferencesTable((Expression) newColumn.getDefaultExpression()); } if (columnsToAdd != null) { for (Column column : columnsToAdd) { checkDefaultReferencesTable((Expression) column.getDefaultExpression()); } } switch (type) { case CommandInterface.ALTER_TABLE_ALTER_COLUMN_NOT_NULL: { if (!oldColumn.isNullable()) { // no change break; } checkNoNullValues(); oldColumn.setNullable(false); db.updateMeta(session, table); break; } case CommandInterface.ALTER_TABLE_ALTER_COLUMN_NULL: { if (oldColumn.isNullable()) { // no change break; } checkNullable(); oldColumn.setNullable(true); db.updateMeta(session, table); break; } case CommandInterface.ALTER_TABLE_ALTER_COLUMN_DEFAULT: { checkDefaultReferencesTable(defaultExpression); oldColumn.setSequence(null); oldColumn.setDefaultExpression(session, defaultExpression); removeSequence(sequence); db.updateMeta(session, table); break; } case CommandInterface.ALTER_TABLE_ALTER_COLUMN_CHANGE_TYPE: { // 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.updateMeta(session, table); } else { oldColumn.setSequence(null); oldColumn.setDefaultExpression(session, null); oldColumn.setConvertNullToDefault(false); if (oldColumn.isNullable() && !newColumn.isNullable()) { checkNoNullValues(); } else if (!oldColumn.isNullable() && newColumn.isNullable()) { checkNullable(); } convertAutoIncrementColumn(newColumn); copyData(); } break; } case CommandInterface.ALTER_TABLE_ADD_COLUMN: { // ifNotExists only supported for single column add if (ifNotExists && columnsToAdd.size() == 1 && table.doesColumnExist(columnsToAdd.get(0).getName())) { break; } for (Column column : columnsToAdd) { if (column.isAutoIncrement()) { int objId = getObjectId(); column.convertAutoIncrementToSequence( session, getSchema(), objId, table.isTemporary()); } } copyData(); break; } case CommandInterface.ALTER_TABLE_DROP_COLUMN: { if (table.getColumns().length == 1) { throw DbException.get(ErrorCode.CANNOT_DROP_LAST_COLUMN, oldColumn.getSQL()); } table.dropSingleColumnConstraintsAndIndexes(session, oldColumn); copyData(); break; } case CommandInterface.ALTER_TABLE_ALTER_COLUMN_SELECTIVITY: { int value = newSelectivity.optimize(session).getValue(session).getInt(); oldColumn.setSelectivity(value); db.updateMeta(session, table); break; } default: DbException.throwInternalError("type=" + type); } return 0; }