what is the use of AND with ORDER BY?

Question

What does the AND do in a query like so

SELECT *
FROM table
WHERE SaleNo > 200,
ORDER BY EmployeeNo AND SaleNo;

How is it different from

SELECT *
FROM table
WHERE SaleNo > 200,
ORDER BY EmployeeNo, SaleNo;

Both queries actually return a table back but I don't understand the meaning of 1st query. ORDER BY is usually used along with pipes and commas for additional filterings. TIA

Answer 1

ORDER BY EmployeeNo AND SaleNo;

The above becomes this:

ORDER BY (EmployeeNo AND SaleNo)

And then becomes:

ORDER BY (true/false AND true/false)

And then

ORDER BY (true/false)

So the expression is converted to a true/false expression.

If the 2 columns are number types, then 0 values = false, and any NON zero value = true

so, you have

  ORDER BY ( (EmployeeNo <> 0) AND (SaleNo <> 0) )

So, if both EmplyeeNo and SaleNo have a value?

You get this

  ORDER BY ( (true) AND (True))

  ORDER BY True

The value is thus -1.

What this means is that if both values have a number, (not 0), then they will appear first in the list and all others if one of the two numbers are 0 or both are 0 will follow.

So, to order by a column, and then by a anohter, you use

col1, col2  - as you have.

if you go

col1 AND col2

Then this is Boolean (true/false) expression, and not a order by one column, and then on to the next.