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Editorial Team
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Asked: 2026-05-29T13:55:31+00:00

Consider the SQL query below: SELECT DISTINCT shops.*, DA.delivery_cost, DA.postcode FROM shops JOIN shops_delivery_area

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Consider the SQL query below:

SELECT DISTINCT shops.*, 
       DA.delivery_cost, 
       DA.postcode 
FROM shops 
       JOIN shops_delivery_area as DA on DA.shop_id = shops.id 
WHERE DA.postcode = "Liverpool" 
      OR location = "Liverpool"

shops table

+----+----------+-----------+----------+
| id | name     | location  | postcode |
+----+----------+-----------+----------+
|  1 | Shop One | Liverpool | L10      |
|  2 | Shop Two | Liverpool | L16      |
+----+----------+-----------+----------+

shops_delivery_area table

+------------------+---------+----------+---------------+
| delivery_area_id | shop_id | postcode | delivery_cost |
+------------------+---------+----------+---------------+
|                1 |       1 | L10      |          0.00 |
|                2 |       1 | L11      |          0.00 |
|                3 |       1 | L12      |          1.00 |
|                4 |       1 | L13      |          1.00 |
|                5 |       2 | L10      |          0.00 |
|                6 |       2 | L16      |          0.00 |
|                7 |       2 | L28      |          0.00 |
+------------------+---------+----------+---------------+

User can search by Postcode (eg: L14, L15, L16) or Location from a textbox.

If user type in “Liverpool”, it will find all the shops that are located in “Liverpool”. The problem is there will be duplicate rows of shop name (shops table). How to solve this issue?

Result (Search by Location):

How to avoid duplication of shop name?

I should do: shops.id = shops_delivery_area.shop_id AND shops.postcode = shops_delivery_area.postcode

+----+----------+-----------+----------+---------------+----------+
| id | name     | location  | postcode | delivery_cost | postcode |
+----+----------+-----------+----------+---------------+----------+
|  1 | Shop One | Liverpool | L10      |          0.00 | L10      |
|  1 | Shop One | Liverpool | L10      |          0.00 | L11      |
|  1 | Shop One | Liverpool | L10      |          1.00 | L12      |
|  1 | Shop One | Liverpool | L10      |          1.00 | L13      |
|  2 | Shop Two | Liverpool | L16      |          0.00 | L10      |
|  2 | Shop Two | Liverpool | L16      |          0.00 | L16      |
|  2 | Shop Two | Liverpool | L16      |          0.00 | L28      |
+----+----------+-----------+----------+---------------+----------+

Result (Search by Postcode L10):
Work fine as expected

+----+----------+-----------+----------+---------------+----------+
| id | name     | location  | postcode | delivery_cost | postcode |
+----+----------+-----------+----------+---------------+----------+
|  1 | Shop One | Liverpool | L10      |          0.00 | L10      |
|  2 | Shop Two | Liverpool | L16      |          0.00 | L10      |
+----+----------+-----------+----------+---------------+----------+
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1 Answer

  1. Editorial Team

    I have managed to get it working. I have used UNION to solve this problem.

    SELECT U.* FROM 
   ((SELECT DISTINCT shops.*, DA.delivery_cost, DA.postcode AS AreaPostcode FROM shops
             JOIN shops_delivery_area2 as DA on DA.shop_id = shops.id
   WHERE DA.postcode = "Liverpool")
  UNION
   (SELECT DISTINCT shops.*, DA.delivery_cost, DA.postcode AS AreaPostcode FROM shops
             JOIN shops_delivery_area2 as DA on DA.shop_id = shops.id AND DA.postcode = shops.postcode
   WHERE shops.location = "Liverpool")) as U

    If there anyway to make this code shorter or improve it, let me know. thanks

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