1. Create a new Custom SQL

Give it a name such as Products - Price Increase SELECTION by X%


2. Add the script below for a price increase

UPDATE
  /*PREFIX*/catalog_product_entity_decimal val
SET
  val.value = (val.value * 1.:`deci.Decimal`)
WHERE
  val.attribute_id = (
    SELECT
      attribute_id
    FROM
      /*PREFIX*/eav_attribute eav
    WHERE
         entity_id in (&`prod.SelProd`)
         AND eav.entity_type_id = 4
         AND eav.attribute_code = 'price'
  );


3. Change the script type to Linked to Products



4. Select your products and run Custom SQL



Follow the same process for setting up a decrease script using the code below


UPDATE
  /*PREFIX*/catalog_product_entity_decimal val
SET
  val.value = (val.value / :`deci.1.10`)
WHERE
  val.attribute_id = (
    SELECT
      attribute_id
    FROM
      /*PREFIX*/eav_attribute eav
    WHERE
      eav.entity_type_id = 4
      AND eav.attribute_code = 'price'
  );