Understanding SQL Server Except with Dev

Hello Dev, in this article, we will discuss one of the most powerful operators in SQL Server – the Except operator. With this tool, you can compare two tables and return only the rows from the first table that are not present in the second table. It’s a simple but incredibly useful tool that can help you save a lot of time and effort when working with large datasets. Let’s dive in and explore this topic further.

What is the Except Operator?

The Except operator is a type of set operator in SQL Server that allows you to compare two sets of data and return only the differences between them. It’s used to subtract one set of data from another set of data and retrieve the result set. The Except operator is used with the SELECT statement and returns all unique rows from the first SELECT statement that are not present in the second SELECT statement.

For example, if you have two tables with the same structure, you can use the Except operator to compare the two tables and return only the rows that are unique to the first table. This is a great way to identify missing or duplicate data in your tables, and it can save you a lot of time when working with large datasets.

How Does the Except Operator Work?

The Except operator works by comparing two sets of data and returning only the differences between them. It does this by performing a set subtraction operation, which means that it subtracts one set of data from another set of data and returns the result set. The result set contains all of the unique rows from the first set that are not present in the second set.

To use the Except operator, you need to specify two SELECT statements that return the data you want to compare. The two SELECT statements must have the same number of columns and the same data types for the corresponding columns. The columns don’t have to be named the same, but they must have the same number of columns and data types.

Using Except with a Single Column

The Except operator can be used with a single column or multiple columns. When using a single column, the syntax is simple:

Column A
1
2
3
4

If we have another table with values 3, 4, 5, 6 in the same column, we can use SELECT Column A FROM Table 1 EXCEPT SELECT Column A FROM Table 2 to return the values 1 and 2 in the first table that are not present in the second table.

Using Except with Multiple Columns

When using multiple columns, the syntax is slightly more complex:

Column A	Column B
1	1
2	2
3	3
4	4

If we have another table with values (2,2), (3,3), (4,5), (5,6) in the same columns, we can use SELECT Column A, Column B FROM Table 1 EXCEPT SELECT Column A, Column B FROM Table 2 to return the values (1,1) in the first table that are not present in the second table.

FAQs

What is the difference between Except and Not In?

The Except operator and the NOT IN operator are both used to compare two sets of data and return only the differences between them. The main difference between the two operators is that the Except operator is more flexible and can be used to compare two sets of data with multiple columns, while the NOT IN operator can only compare two sets of data with a single column.

What is the difference between Except and Union?

The Except operator and the Union operator are both set operators in SQL Server. The main difference between the two operators is that the Except operator returns only the rows that are unique to the first SELECT statement, while the Union operator returns all of the unique rows from both SELECT statements.

Can I use the Except operator with more than two tables?

Yes, you can use the Except operator with more than two tables. To do this, you need to specify multiple SELECT statements using the same syntax as before. The result set will contain all of the unique rows from the first SELECT statement that are not present in any of the other SELECT statements.

What happens if the two tables have different data types?

If the two tables have different data types for the corresponding columns, you will get an error message when you try to use the Except operator. To avoid this, you need to make sure that the two tables have the same data types for the corresponding columns.

Can I use the Except operator with subqueries?

Yes, you can use the Except operator with subqueries. To do this, you need to include the subqueries in the SELECT statement using the same syntax as before.

Conclusion

The Except operator is a powerful and flexible tool in SQL Server that can help you save a lot of time and effort when working with large datasets. By allowing you to compare two sets of data and return only the differences between them, you can quickly identify missing or duplicate data in your tables. Whether you’re a beginner or an experienced SQL Server user, the Except operator is a must-know tool that will make your work much easier.