Question

Suppose we got a original query as follows:

SELECT A, B, C FROM tblA

Now, I need to additional artificial rows like
SELECT ‘Kyala’, B, C FROM tblA when, for example, C = 100 to be inserted into the resultset.

As an example, if the tblA hold one row:

A      B      C
John   1      100

my goal is to return two rows like below with a single SQL query.

A      B      C
John   1      100
Kyala  1      100

How could I achieve it using a single SQL instead of relying on table variable or temp table?

Answer 1

You could achieve this with the UNION operator.

SELECT A, B, C from tblA
UNION
SELECT 'Kyala', B, C FROM tblA WHERE C = 100

In response to the question in the comments about improving performance so that the table is only queried once – you could add a covering index over columns C and B so that the second part of the query uses that index rather than querying the table:

CREATE NONCLUSTERED INDEX [IX_tblA_CD] ON [dbo].[tblA] 
(
    [C] ASC
)
INCLUDE ( [B]) ON [PRIMARY]
GO

However, depending on the use case (this sounds like some kind of ad-hoc process for testing?), you might prefer to take the hit of two table scans rather than adding a new index which might not be appropriate for use in production.