an element with the same SQL SERVER key has already been added

All we need is an easy explanation of the problem, so here it is.

Good morning community, I am having problems when I run this query from SQL 2018 and Visual basic 2010 shows me the following error "an element with the same key has already been added"

SELECT DESCRIPCION AS nodeText,'DEPA' + CAST(IDDEPARTAMENTO AS VARCHAR) AS nodeKey,''AS nodeParentKey FROM DEPARTAMENTO
UNION ALL
SELECT DESCRIPCION AS nodeText,'PROV' + CAST(IDPROVINCIA AS VARCHAR) AS nodeKey,
'DEPA' + CAST(IDDEPARTAMENTO AS VARCHAR) AS nodeParentKey FROM PROVINCIA
UNION ALL
SELECT DESCRIPCION AS nodeText,'DIST' + CAST(IDUBIGEO AS VARCHAR) AS nodeKey,
'PROV' + CAST(IDPROVINCIA AS VARCHAR) AS nodeParentKey FROM ubigeo

As I can avoid duplicate elements, I think it is with the DISTINCT clause but I have no idea where this clause can go, please support

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

use UNION instead of UNION ALL in this way:

SELECT DESCRIPCION AS nodeText,'DEPA' + CAST(IDDEPARTAMENTO AS VARCHAR) AS 
nodeKey,''AS nodeParentKey FROM DEPARTAMENTO
UNION ALL
SELECT DESCRIPCION AS nodeText,'PROV' + CAST(IDPROVINCIA AS VARCHAR) AS nodeKey,
'DEPA' + CAST(IDDEPARTAMENTO AS VARCHAR) AS nodeParentKey FROM PROVINCIA
UNION
SELECT DESCRIPCION AS nodeText,'DIST' + CAST(IDUBIGEO AS VARCHAR) AS nodeKey,
'PROV' + CAST(IDPROVINCIA AS VARCHAR) AS nodeParentKey FROM ubigeo

it will remove duplicates

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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