Question

I have the following table called Attributes

* AttId  * CustomerId  * Class * Code *
| 1      | 1           | 1     | AA   |
| 2      | 1           | 1     | AB   |
| 3      | 1           | 1     | AC   |
| 4      | 1           | 2     | AA   |
| 5      | 1           | 2     | AB   |
| 6      | 1           | 3     | AB   |
| 7      | 2           | 1     | AA   |
| 8      | 2           | 1     | AC   |
| 9      | 2           | 2     | AA   |
| 10     | 3           | 1     | AB   |
| 11     | 3           | 3     | AB   |
| 12     | 4           | 1     | AA   |
| 13     | 4           | 2     | AA   |
| 14     | 4           | 2     | AB   |
| 15     | 4           | 3     | AB   |

Where each Class, Code pairing represents a specific Attribute.

I’m trying to write a query that returns all customers that are NOT linked to the Attribute pairing Class = 1, Code = AB.

This would return Customer Id values 2 and 4.

I started to write Select Distinct A.CustomerId From Attributes A Where (A.Class = 1 and A.Code = 'AB') but stopped when I realised I was writing a SQL query and there is not an operator available to place before the parentheses to indicate the clause within must Not be met.

What am I missing? Or which operator should I be looking at?

Edit:

I’m trying to write a query that only returns those Customers (ie distinct Customer Id’s) that have NO link to the Attribute pairing Class = 1, Code = AB.

This could only be Customer Id values 2 and 4 as the table does Not contain the rows:

* AttId  * CustomerId  * Class * Code *
| x      | 2           | 1     | AB   |
| x      | 4           | 1     | AB   |

Changed Title from:

How to write “Where Not(a=x and b=x)”in Sql Query

To:

How to write a Sql query to find distinct values that have never met the following “Where Not(a=x and b=x)”

As the previous title was a question in it’s own right however the detail of the question added an extra dimension which led to confusion.

Answer 1

One way would be

SELECT DISTINCT CustomerId FROM Attributes a 
WHERE NOT EXISTS (
    SELECT * FROM Attributes forbidden 
    WHERE forbidden.CustomerId = a.CustomerId AND forbidden.Class = _forbiddenClassValue_ AND forbidden.Code = _forbiddenCodeValue_
)

or with join

SELECT DISTINCT a.CustomerId FROM Attributes a
LEFT JOIN (
    SELECT CustomerId FROM Attributes
    WHERE Class = _forbiddenClassValue_ AND Code = _forbiddenCodeValue_
) havingForbiddenPair ON a.CustomerId = havingForbiddenPair.CustomerId
WHERE havingForbiddenPair.CustomerId IS NULL

Yet another way is to use EXCEPT, as per ypercube’s answer