Updating a set of values using criteria from multiple tables - sql

Question

Given a specific set of rows that I've queried I want to update the "ifSpeed" value on each of them to a static value of 1000000000.
I have created a query to find all the specific rows that I need to update that value in, but had to join two tables to get that information, due to the the tag I'm using being in a separate table.
I have created a query to find all the specific rows that I need to update that value in, but had to join two tables to get that information, due to the the tag I'm using being in a separate table. That query is the first block of code. The second is one of my attempts at updating the values. I've also looked into subqueries, but my SQL is very rusty as it has been about 8 years since I've worked with it.
SELECT ifSpeed
FROM master_dev.device_interfaces AS MDDI
JOIN master_dev.device_interface_tags_map AS MDDITM
ON MDDI.if_id = MDDITM.if_id
WHERE ifSpeed=10000000
AND MDDITM.tag_id=13
UPDATE master_dev.device_interfaces
SET ifSpeed = '1000000000'
FROM master_dev.device_interfaces AS MDDI
JOIN master_dev.device_interface_tags_map AS MDDITM
ON MDDI.if_id = MDDITM.if_id
WHERE ifSpeed=10000000
AND MDDITM.tag_id=13
My expectation is that all rows that exist in my SELECT query have their ifSpeed updated to 1000000000.
What actually happens is simply an error. I'm using a restricted interface to query the DB and it only provides rows affected, the data from the rows or simply "ERROR". Very helpful... I know.

Answer 1

in SSMS try Below
---- Updated ---
UPDATE MDDI
SET ifSpeed = '1000000000'
FROM master_dev.dbo.device_interfaces AS MDDI
JOIN master_dev.dbo.device_interface_tags_map AS MDDITM
ON MDDI.if_id = MDDITM.if_id
WHERE ifSpeed = 10000000
AND MDDITM.tag_id = 13

Answer 2

The syntax of UPDATE that has a FROM clause is rather cumbersome. Luckily in SQL Server there is a better way.
I usually use CTE (common-table expression) in this case, which makes the query very easy to write and read and verify that it works as intended.
So, you have your complex SELECT statement that returns all the rows that you want to update. Great.
SELECT ifSpeed
FROM
master_dev.device_interfaces AS MDDI
JOIN master_dev.device_interface_tags_map AS MDDITM
ON MDDI.if_id = MDDITM.if_id
WHERE
ifSpeed=10000000
AND MDDITM.tag_id=13
;
Now, wrap it into CTE and update the CTE:
WITH
CTE
AS
(
SELECT ifSpeed
FROM
master_dev.device_interfaces AS MDDI
JOIN master_dev.device_interface_tags_map AS MDDITM
ON MDDI.if_id = MDDITM.if_id
WHERE
ifSpeed=10000000
AND MDDITM.tag_id=13
)
UPDATE CTE
SET ifSpeed = '1000000000'
;
You can write SELECT * FROM CTE instead of the line UPDATE CTE SET ... before performing an actual update to verify that you are selecting correct rows.

Answer 3

Thanks for all the input on this! Unfortunately I had two different teams give me two different answers. While I supposedly was able to do this after escalating further up the chain the engineering team on the backend put up a brick wall saying don't risk the DB tables. That decision baffles me based on what's affected, but not my call to make I suppose.
That being said they did let me know that the original code was fine and likewise the variation that maSTAShuFu provided.
#Vladimir - Sorry didn't get to try your's out, but I'm definitely keeping it in my back pocket. Thank you!