Using IF / ELSE to determine a SELECT INTO statement - sql

Question

I'm having some strange issues using IF / ELSE to determine which one or two SELECT statements to execute. The error message I'm getting when running the full statement is that my temporary table already exists, but that does not occur if I run two separate executions of two separate IF statements.
Here is the code in SQL Server:
IF (select BusinessDayCount from Calendartbl) <= 1
BEGIN
SELECT * into #temp1
FROM PreviousMonthTbl
END
ELSE
BEGIN
SELECT * into #temp1
FROM CurrentMonthTbl
END

Answer 1

It's a "feature" of the syntax checking in SQL Server. You simply cannot "create" a #temporary table twice within the same batch.
This is the pattern you need.
SELECT * into #temp1
FROM PreviousMonthTbl
WHERE 1=0;
IF (select BusinessDayCount from Calendartbl) <= 1
BEGIN
INSERT into #temp1 SELECT *
FROM PreviousMonthTbl
END
ELSE
BEGIN
INSERT into #temp1 SELECT *
FROM CurrentMonthTbl
END
If you prefer, you can also express the branch (in this case) as a WHERE clause:
SELECT * into #temp1
FROM PreviousMonthTbl
WHERE (select BusinessDayCount from Calendartbl) <= 1
UNION ALL
SELECT *
FROM CurrentMonthTbl
WHERE isnull((select BusinessDayCount from Calendartbl),2) > 1

Answer 2

You can't use SELECT INTO for a tables with same name in the same batch. Use a different name for a temporary table
IF EXISTS(
SELECT 1
FROM Calendartbl
WHERE BusinessDayCount <= 1
)
BEGIN
IF OBJECT_ID('tempdb.dbo.#PreviousMonthTbl') IS NULL DROP TABLE dbo.#PreviousMonthTbl
SELECT *
INTO #PreviousMonthTbl
FROM PreviousMonthTbl
END
ELSE
BEGIN
IF OBJECT_ID('tempdb.dbo.#CurrentMonthTbl') IS NULL DROP TABLE dbo.#CurrentMonthTbl
SELECT *
INTO #CurrentMonthTbl
FROM CurrentMonthTbl
END

Answer 3

From what I understand the problem is this:
When you run the below statement,
SELECT * into #temp1 FROM CurrentMonthTbl
you are creating a temp table on the fly.
If before that line you had a create table statement, then this Select into statement will fail because the table already exists.
If in your case you already have a temp table created, then try replacing:
SELECT * into #temp1 FROM CurrentMonthTbl
with:
Insert into #temp1
Select * from CurrentMonthTbl
Also look at There is already an object named '##Temp' in the database

Answer 4

You can use actual table in place of #temp1 table in if else statement. After that you can insert the data from actual to temp table and drop the actual table.
IF OBJECT_ID('tempdb..#temp1') is not null
drop table #temp1
IF (select BusinessDayCount from Calendartbl) <= 1
BEGIN
SELECT * into dbo.TempTable
FROM PreviousMonthTbl
END
ELSE
BEGIN
SELECT * into dbo.TempTable
FROM CurrentMonthTbl
END
select * into #temp1
from dbo.TempTable
IF OBJECT_ID('dbo.TempTable', 'U') is not null
drop table dbo.TempTable