Dynamically choose one of two columns based on a third column

Question

I have 3 tables, lets say tables A, B, C to obfuscate my software :). A and B have two columns with numeric values and Table C has a Boolean column.

What I want is to create a view with a single column where depending on the column in C, either the value in A or B is selected.

Example:

Input:

        | A.val |    | B.val |    | C.val |
        ---------    ---------    ---------
entry1  |   1   |    |   6   |    |   T   |
entry2  |   2   |    |   8   |    |   F   |

Output:

       | D |
       -----
entry1 | 1 |
entry2 | 8 |

I'm wondering if there is a way to do this in a SQL statement(s) since I am currently doing it programmatically which eats up unnecessary resources.

you should show the table structures and mention the keys in those tables — Vamsi Prabhala, Sep 15 '15 at 21:32
This may help: http://stackoverflow.com/questions/17598350/select-value-if-condition-in-sql-server — Robert, Sep 15 '15 at 21:37
vkp, The keys are "entry1", "entry2". Probably could've made that more clear. — mascoj, Sep 16 '15 at 13:44

score 7 · Accepted Answer · answered Sep 15 '15 at 21:37

7

If you're trying to select A if C = T or B if C = F then you can just use a Case Statement

Select (Case When C.val = TRUE Then A.val Else B.Val END) AS D
From Table

answered Sep 15 '15 at 21:37

JamieD77

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Thanks! Works great. Don't know how I skimmed over the existence of 'CASE' – mascoj Sep 15 '15 at 22:32

score 0 · Answer 2 · answered Sep 15 '15 at 21:36

0

You can use CASE syntax for that.

SELECT CASE WHEN C.val = 'T' THEN A.val ELSE B.val END as yourField

answered Sep 15 '15 at 21:36

Elon Than

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Dynamically choose one of two columns based on a third column

2 Answers2