SET @s = (SELECT IF(
    (SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE table_schema = DATABASE()
     AND table_name = 'Monitors'
     AND column_name = 'Encoder'
    ) > 0,
"SELECT 'Column Encoder already exists in Monitors'",
"ALTER TABLE `Monitors` ADD `Encoder`     enum('auto','h264','libx264','h264_omx','h264_vaapi','mjpeg','mpeg1','mpeg2')  AFTER `OutputCodec`"
));

PREPARE stmt FROM @s;
EXECUTE stmt;
ALTER TABLE `Monitors` MODIFY `Encoder`     enum('auto','h264','libx264', 'h264_omx', 'h264_vaapi', 'mjpeg','mpeg1','mpeg2');

ALTER TABLE `Monitors` MODIFY `OutputCodec`     INT UNSIGNED default 0;