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Guys , I saw the following expression in a sql video:
(union select 1,2,3 )
What does it mean ?
video link: https://www.youtube.com/watch?v=N0zAChmZIZU
1 answer
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The function of the operator UNION is to return the DISTINCT RESULTS of 2 SELECTS or more ( to list also the repeated results is used UNION ALL )
An example of use would be to list all cities in a table client together with a table supplier
Example:
SELECT cidade FROM Cliente UNION SELECT cidade FROM Fornecedor
If you have only 2 customers , 1 living in São Paulo and the other in Rio de Janeiro , and only 1 Supplier , from São Paulo the query will return:
São Paulo
Rio de Janeiro
Using UNION ALL for the same data:
Example :
SELECT cidade FROM Cliente UNION ALL SELECT cidade FROM Fornecedor
Upshot:
São Paulo
São Paulo
Rio de Janeiro
The video it’s about SQL INJECTION
A page that displays 3 data appears and the author uses the UNION in a query string to display 1 , 2 and 3 instead of the original data. Then it replaces the code to steal data and credentials.
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Do you expect people to have to follow the video to answer you? It would be nicer if you left the self-explanatory question and reproduced the whole example here.
– Bacco