Updating with select in sql server

Orders AS O GROUP BY O.customer_id )OA ON C.customer_id = OA.customer_id; UPDATE C SET /* SELECT *, -- */ order_count = FROM dbo.

Orders AS O GROUP BY O.customer_id )OA ON C.customer_id = OA.customer_id; table while pulling in necessary information from other table(s) referenced in the statement.

Adding a WHERE clause would limit the result set of the JOINed table as well.

FROM Specifies that a table, view, or derived table source is used to provide the criteria for the update operation. If the object being updated is the same as the object in the FROM clause and there is only one reference to the object in the FROM clause, an object alias may or may not be specified.

If the object being updated appears more than one time in the FROM clause, one, and only one, reference to the object must not specify a table alias.

Orders AS O GROUP BY O.customer_id ), customer_order_counts AS ( SELECT C.customer_id, C.name, C.order_count, new_order_cnt FROM dbo.

Customers AS C JOIN order_counts AS OC ON C.customer_id = OC.customer_id ) UPDATE COC SET /* SELECT *, -- */ order_count = COC.new_order_cnt FROM customer_order_counts AS COC; would happily update each customer multiple times, each time overwriting the prior change. The problem with that is that there is no guarantee in which order that happens.

Before I show you the multi-table solution, let me demonstrate the simplest form of the --UPDATE C SET /* SELECT *, -- */ order_count = FROM dbo.

Customers AS C JOIN( SELECT O.customer_id, COUNT(1) cnt FROM dbo.

If CTEs are your thing, you can even go a step further with this.

As long as SQL Server can easily determine what you are intending to update, you can actually "UPDATE" a CTE directly using a very similar syntax: WITH order_counts AS ( SELECT O.customer_id, COUNT(1) cnt FROM dbo.

Specifies the condition to be met for the rows to be updated.

The search condition can also be the condition upon which a join is based.

In the following lines, I am going to show you three tricks that have made my life simpler on many occasions.