SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax — PHP — PDO [duplicate]

Answer 1

ALTER TABLE `{$installer->getTable('sales/quote_payment')}`
ADD `custom_field_one` VARCHAR( 255 ) NOT NULL,
    ADD `custom_field_two` VARCHAR( 255 ) NOT NULL;

Add backtick i.e. " ` " properly. Write your getTable name and column name between backtick.