# SQL SERVER – Solution Part 2 – A Quick Puzzle on JOIN and NULL – SQL Brain Teaser

Some questions are timeless and they never grow old; no matter how much they grow old their interest never dies. Earlier, I asked a simple puzzle based on a conversation on SQLAuthority Page, and have received an overwhelming response from readers. I still get emails related to this puzzle every day.

Before we move on, I suggest you read the question and its initial solution here:

The puzzle had three parts and the users had to fill up the second part, which I had left it for them to complete. I received many responses, and here is another response which is absolutely valid and worthy of acknowledgment. Once again, before you read the solution, I suggest you give the puzzle a quick try. Perhaps you’d find another neat way to solve this puzzle.

1. Setup
2. Fill in the blanks – T-SQL code
3. Query and Resultset

Just like this puzzle, there are many other learning nuggets in our SQL Server Questions and Answers course online.

## Complete Solution Query

```USE TempDB GO -- Sample Table CREATE TABLE FirstTable (Col1 INT) CREATE TABLE SecondTable (Col1 INT) GO ALTER TABLE FirstTable ADD CONSTRAINT UX_FirstTable UNIQUE NONCLUSTERED (Col1); ALTER TABLE SecondTable ADD CONSTRAINT UX_SecondTable UNIQUE NONCLUSTERED (Col1); GO INSERT INTO FirstTable (Col1) VALUES (NULL) GO INSERT INTO SecondTable (Col1) VALUES (NULL) GO -------------------------------------- -- Solution SELECT st.col1 FROM FirstTable ft RIGHT JOIN SecondTable st ON st.Col1 = ft.Col1 UNION ALL SELECT st.col1 FROM FirstTable ft LEFT JOIN SecondTable st ON st.Col1 = ft.Col1 GO DROP TABLE FirstTable; DROP TABLE SecondTable; GO ```

Now the reason I did not selected this as a valid answer is because if you notice original solution required to insert one row into the FirstTable. However, when you look at carefully, you can notice even this solution is valid solution. There were many other solution which require to change T-SQL which I initially provided, however as per the puzzle that was not allowed.

Any other solution out there?

Reference: Pinal Dave (http://blog.sqlauthority.com)

## 5 thoughts on “SQL SERVER – Solution Part 2 – A Quick Puzzle on JOIN and NULL – SQL Brain Teaser”

1. Ganesh narim |

Hi pinal,

How are you doing..?

I feel happy to say that this “JOINS and NULL” issue came up with earlier blog comments you know that is your first reply to me i have commented on some posts before but i did not get any reply for that, i was happy when i found response for this post

That time i was bit confusing when i was seaing the answer for query 1. suddenly i thought why jeff facing the duplicate problem with Joins even that join query1 not showing all including NULL’s,

i was serously thinking for some time i did some work later i realised with “NULL is NULL” and ‘not NULL=NULL’..

However in this post you are right i have thought it earlier in “SQL SERVER – Solution – A Quick Puzzle on JOIN and NULL – SQL Brain Teaser” but you mentioned clearly that not changing the T-SQL qury, if you ok with chaning the Query we have another solution for getting NULL valuse from both the tables.
(without using joins).

SELECT * FROM dbo.FirstTable
WHERE dbo.FirstTable.Col1 IS NULL

UNION ALL

SELECT * FROM dbo.SecondTable
WHERE dbo.SecondTable.Col1 IS NULL

2. Khurram Amin |

Hi Pinal
I initially wrong this but later today I run both queries and there is difference in execution plan as well, can you please explain two quries. Thanks,

SELECT st.col1
FROM FirstTable ft
Full OUTER JOIN SecondTable st ON st.Col1 = ft.Col1

Khurram

3. How we can call a store procedure in crystal report

4. Hi Pinal Sir,
Thank you for selecting this as one of the answer for puzzle.

Thank\$
Chirag Satasiya