How to use Join with like operator and then casting columns - sql

Question

I have 2 tables with these columns:
CREATE TABLE #temp
(
Phone_number varchar(100) -- example data: "2022033456"
)
CREATE TABLE orders
(
Addons ntext -- example data: "Enter phone:[phone]<br>Thephoneisvalid"
)
I have to join these two tables using 'LIKE' as the phone numbers are not in same format. Little background I am joining the #temp table on the phone number with orders table on its Addons value. Then again in WHERE condition I am trying to match them and get some results. Here is my code. But my results that I am getting are not accurate. As its not returning any data. I don't know what I am doing wrong. I am using SQL Server.
select
*
from
order_no as n
join
orders as o on n.order_no = o.order_no
join
#temp as t on t.phone_number like '%'+ cast(o.Addons as varchar(max))+'%'
where
t.phone_number = '%' + cast(o.Addons as varchar(max)) + '%'

Answer 1

You can not use LIKE statement in the JOIN condition. Please provide more information on your tables. You have to convert the format of one of the phone field to compile with other phone field format in order to join.

Answer 2

I think your join condition is in the wrong order. Because your question explicitly mentions two tables, let's stick with those:
select *
from orders o JOIN
#temp t
on cast(o.Addons as varchar(max)) like '%' + t.phone_number + '%';
It has been so long since I dealt with the text data type (in SQL Server), that I don't remember if the cast() is necessary or not.

Answer 3

Instead of trying to do everything in a single top-level query, you should apply a transformation projection to your orders table and use that as a subquery, which will make the query easier to understand.
Using the CHARINDEX function will make this a lot easier, however it does not support ntext, you will need to change your schema to use nvarchar(max) instead - which you should be doing anyway as ntext is deprecated, fortunately you can use CONVERT( nvarchar(max), someNTextValue ), though this will reduce performance as you won't be able to use any indexes on your ntext values - but this query will run slowly anyway.
SELECT
orders2.*,
CASE WHEN orders2.PhoneStart > 0 AND orders2.PhoneEnd > 0 THEN
SUBSTRING( orders2.Addons, orders2.PhoneStart, orders2.PhoneEnd - orders2.PhoneStart )
ELSE
NULL
END AS ExtractedPhoneNumber
FROM
(
SELECT
orders.*, -- never use `*` in production, so replace this with the actual columns in your orders table
CHARINDEX('Enter phone:', Addons) AS PhoneStart,
CHARINDEX('<br>Thephoneisvalid', AddOns, CHARINDEX('Enter phone:', Addons) ) AS PhoneEnd
FROM
orders
) AS orders2
I suggest converting the above into a VIEW or CTE so you can directly query it in your JOIN expression:
CREATE VIEW ordersWithPhoneNumbers AS
-- copy and paste the above query here, then execute the batch to create the view, you only need to do this once.
Then you can use it like so:
SELECT
* -- again, avoid the use of the star selector in production use
FROM
ordersWithPhoneNumbers AS o2 -- this is the above query as a VIEW
INNER JOIN order_no ON o2.order_no = order_no.order_no
INNER JOIN #temp AS t ON o2.ExtractedPhoneNumber = t.phone_number
Actually, I take back my previous remark about performance - if you add an index to the ExtractedPhoneNumber column of the ordersWithPhoneNumbers view then you'll get good performance.