Presence and absence

Improving Query Performance in SQL Server

Dean Smith

Founder, Atamai Analytics

Venn diagram - presence

Data present in both tables.

Venn Diagram Presence

Data present in the left table but absent in the right table.

Venn Diagram Absence

Customers Orders Database

SELECT CustomerID
FROM Customers






SELECT CustomerID
FROM Orders;

SELECT CustomerID
FROM Customers


INTERSECT


SELECT CustomerID
FROM Orders;

SELECT CustomerID
FROM Customers






SELECT CustomerID
FROM Orders;

SELECT CustomerID
FROM Customers


EXCEPT


SELECT CustomerID
FROM Orders;

CustomerID
FISSA
PARIS

Advantages

Disadvantages

The number and order of columns in the SELECT statement must be the same between queries

Improving Query Performance in SQL Server