How can I convert 2 queries into single query

I have the following table and I try to extract all lines with the B value for the fields RefD and all lines whose RefA fields to the value B and the value of their RefD fields is among those with value B for the fields RefD. If my table contains:
RefA ..... RefD
..K ........W
..Z ....... E
..A ........ B
..C ........ B
D ........ B
B ........ C
B ........ H

the result is that waiting

RefA RefD ....
A...... B
C ..... B
D ..... B
B ..... C


At the moment I made the two requests
the first on my table

Code:

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SELECT * FROM TABLE WHERE RefD=B

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And the second on the outcome of the requests

Code:

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SELECT * FROM TABLE WHERE RefD=A OR RefD=C OR RefD=D

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I want to know if it is possible to do this in one query.

When you write

Quote:

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extract all lines with the B value for the fields RefD and all lines whose RefA fields to the value B and the value of their RefD fields is among those with the value B for the fields RefD.

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I think from reading your example and your code that you wanted to write:

Quote:

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extract all lines with the B value for the fields RefD and all lines whose RefA fields to the value B and the value of their RefD fields is among those not having value B for the fields RefD.

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If so:

Code:

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  SELECT * 
  FROM TABLE 
  WHERE RefD = 'B'
  OR (RefA = 'B' AND RefD <> 'B')

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A union is sufficient

Code:

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SELECT * FROM TABLE WHERE RefD=B
UNION
SELECT * FROM TABLE WHERE RefD IN (A, C, D)

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@ Modifier

No it does not work because if you apply this solution to my example the line
"B ........ H" will appear which is not needed.

@ XSI

Except that I do not know the values A, C, D in advance, that is why I make 2 requests at this time.

Use a subquery:

Code:

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SELECT * FROM TABLE 
  WHERE RefD = B OR (RefA=B AND RefD IN ( SELECT RefD FROM TABLE WHERE RefD=B))

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