What is the order of execution for this SQL statement

Solution 1:

Check out the documentation for the SELECT statement, in particular this section:

Logical Processing Order of the SELECT statement

The following steps show the logical processing order, or binding order, for a SELECT statement. This order determines when the objects defined in one step are made available to the clauses in subsequent steps. For example, if the query processor can bind to (access) the tables or views defined in the FROM clause, these objects and their columns are made available to all subsequent steps. Conversely, because the SELECT clause is step 8, any column aliases or derived columns defined in that clause cannot be referenced by preceding clauses. However, they can be referenced by subsequent clauses such as the ORDER BY clause. Note that the actual physical execution of the statement is determined by the query processor and the order may vary from this list.

which gives the following order:

FROM
ON
JOIN
WHERE
GROUP BY
WITH CUBE or WITH ROLLUP
HAVING
SELECT
DISTINCT
ORDER BY
TOP

Solution 2:

WHERE
ORDER BY
TOP

Here is a good article about that: http://blog.sqlauthority.com/2009/04/06/sql-server-logical-query-processing-phases-order-of-statement-execution/

Solution 3:

Simply remember this phrase:- Fred Jones' Weird Grave Has Several Dull Owls

Take the first letter of each word, and you get this:-

FROM
(ON)
JOIN
WHERE
GROUP BY
(WITH CUBE or WITH ROLLUP)
HAVING
SELECT
DISTINCT
ORDER BY
TOP

Hope that helps.

Solution 4:

This is exact execution order, with your case.

1-FROM
2-WHERE
3-SELECT 
4-ORDER BY
5-TOP

Solution 5:

TOP, WHERE, and ORDER BY are not "executed" - they simply describe the desired result and the database query optimizer determines (hopefully) the best plan for the actual execution. The separation between "declaring the desired result" and how it is physically achieved is what makes SQL a "declarative" language.

Assuming there is an index on CustomerSalary, and the table is not clustered, your query will likely be executed as an index seek + table heap access, as illustrated in this SQL Fiddle (click on View Execution Plan at the bottom):

enter image description here

As you can see, first the correct CustomerSalary value is found through the Index Seek, then the row that value belongs to is retrieved from the table heap through RID Lookup (Row ID Lookup). The Top is just for show here (and has 0% cost), as is the Nested Loops for that matter - the starting index seek will return (at most) one row in any case. The whole query is rather efficient and will likely cost only a few I/O operations.

If the table is clustered, you'll likely have another index seek instead of the table heap access, as illustrated in this SQL Fiddle (note the lack of NONCLUSTERED keyword in the DDL SQL):