Insert 2 rows when a condition verified - sql-server

Question

I have a SELECT INTO #tTable SELECT CASE WHEN condition THEN value1 ELSE value2 query.
When a particular condition is verified I have to insert into #tTable 2 rows instead of 1 that differ each other only for 1 column.
I resolved this problem in this way:
Insert into #tTable a foo row with value for my column v1v2
Insert into #tTable value1 where col = v1v2
Insert into #tTable value2 where col = v1v2
Delete from #tTable where col = v1v2
Is there a better and more performance way to do this? Is there a way to insert 2 rows in an INSERT INTO #table SELECT CASE WHEN statement?
Example:
INSERT INTO #tTable (col1, col2, col3)
SELECT T.col1, T.col2, CASE WHEN T.col1 > T.col2 THEN v1v2
WHEN T.col1 = T.col2 THEN value1 ELSE value2 END
FROM Table1 as T;
INSERT INTO #tTable (col1, col2, col3)
SELECT T.col1, T.col2, value1
FROM Table1 as T
WHERE T.col3 = v1v2;
INSERT INTO #tTable (col1, col2, col3)
SELECT T.col1, T.col2, value2
FROM Table1 as T
WHERE T.col3 = v1v2;
DELETE FROM #tTable
WHERE col3 = v1v2;
I have to insert 2 rows (one with value1 and other with value2) on case when T.col1 > T.col2
EDIT:
Actually, my query is like this:
INSERT INTO #tTable (col1, col2, col3)
SELECT T.col1, T.col2,
CASE WHEN condition1 AND condition2 AND condition3 THEN value1
WHEN condition4 AND condition5 AND condition6 THEN value2
WHEN condition7 AND condition8 AND condition9 THEN v1v2 END
FROM Table1 as T

Answer 1

You can't generate another row with a CASE, you will have to use UNION ALL or an additional INSERT. The simplest way I see it is with a UNION ALL, repeating the condition for v1 + v2 on each SELECT:
INSERT INTO #tTable (
col1,
col2,
col3)
SELECT
V.Col1,
V.Col2,
col3 = V.value1
FROM
Table1 AS V
WHERE
(condition1 AND condition2 AND condition3) OR -- value1 condition
(condition7 AND condition8 AND condition9) -- shared condition
UNION ALL
SELECT
V.Col1,
V.Col2,
col3 = V.value2
FROM
Table1 AS V
WHERE
(condition4 AND condition5 AND condition6) OR -- value2 condition
(condition7 AND condition8 AND condition9) -- shared condition
If your conditions are bound to change or are complex, you can write them only once if you place them on a CTE and reference their output:
;WITH DataWithConditions AS
(
SELECT
T.Col1,
T.Col2,
T.Value1,
T.Value2,
Condition = CASE
WHEN condition1 AND condition2 AND condition3 THEN 1
WHEN condition4 AND condition5 AND condition6 THEN 2
WHEN condition7 AND condition8 AND condition9 THEN 3 END
FROM
Table1 AS T
)
INSERT INTO #tTable (
col1,
col2,
col3)
SELECT
V.Col1,
V.Col2,
col3 = V.value1
FROM
DataWithConditions AS V
WHERE
V.Condition IN (1, 3)
UNION ALL
SELECT
V.Col1,
V.Col2,
col3 = V.value2
FROM
DataWithConditions AS V
WHERE
V.Condition IN (2, 3)

Answer 2

You can try UNION ALL to incorporate the second column's value as ROW as shown below-
INSERT INTO #tTable (col1, col2, col3)
SELECT T.col1, T.col2,
CASE
WHEN T.col1 > T.col2 THEN value1 -- Column name may be v1v2
WHEN T.col1 = T.col2 THEN value1
ELSE value2
END
FROM Table1 AS T
UNION ALL
SELECT T.col1, T.col2,value2 -- Value2 I guess the 2nd column
FROM Table1 AS T WHERE T.col1 > T.col2