MERGE between 2 tables, one table with 10million rows - sql-server

Question

TableA
match / Keyword
0 Stackoverflow
1 Youtube
1 Google
0 Yandex
1 Twitter
0 Facebook
0 Teacher
Totally 10million rows in TableA
There is Clustered index at Keyword column
TableB
match / word
1 You
1 Go
1 Twit
0 Home
0 Car
0 Pencil
0 Money
0 Weather
0 Her
Totally 500 rows in TableB
There is Clustered index at word column
My Question
i want to make a sql query to match every word from TableB if matches in TableA keywords. And update the TableB.match with 1
(TableA.keyword like '+TableB.word+'%') (will be matched)
NOT the middle of the keyword matches; (TableA.keyword like '%'+TableB.word+'%')
Forexample Her -> in Teacher (wont be matched)
I Tried to use MERGE
First Try;
i tried to match keywords with words and update TableB
i get error, because there is multiple matches in TableA and MERGE do not allow updating multiple times a row in Target table (TableB)
MERGE INTO [TableB] As XB
USING (Select keyword FROM [TableA]) As XA
ON XB.word LIKE ''+XA.keyword+'%'
WHEN MATCHED THEN UPDATE SET XB.match=1;
Second Try;
i tried to match words with keywords and update TableA
i get what i want, The problem is, it takes 1 hour to execute the query for 500words in 10million keywords.
MERGE INTO [TableA] As XA
USING (Select word FROM [TableB]) As XB
ON XB.word LIKE ''+XA.keyword+'%'
WHEN MATCHED THEN UPDATE SET XA.match=1;
Is there an option to fasten these lookups in SecondTry?

Answer 1

An update statement will suffice for what you're trying to do. Note that this will probably not perform very well as SQL isn't great at comparing strings.
declare #a table (match int, keyword varchar(50))
declare #b table (match int, keyword varchar(50))
insert into #a values (0, 'Stackoverflow')
insert into #a values (0, 'Youtube')
insert into #a values (0, 'Google')
insert into #a values (0, 'Yandex')
insert into #a values (0, 'Twitter')
insert into #a values (0, 'Facebook')
insert into #a values (0, 'Teacher')
insert into #b values (0, 'You')
insert into #b values (0, 'Go')
insert into #b values (0, 'Twit')
insert into #b values (0, 'Home')
insert into #b values (0, 'Car')
insert into #b values (0, 'Pencil')
insert into #b values (0, 'Money')
insert into #b values (0, 'Weather')
insert into #b values (0, 'Her')
--commented out because user didn't want this, but it matches the provided data
--update #a
--set match = 1
--where keyword in
--(
-- select
-- distinct a.keyword
-- from #a a
-- cross apply #b b
-- where a.keyword like b.keyword + '%'
--)
update #b
set match = 1
where keyword in
(
select
distinct b.keyword
from #a a
cross apply #b b
where a.keyword like b.keyword + '%'
)
select *
from #a
select *
from #b
--EDIT BY Sean--
Here is how you could do this as a correlated subquery so you can use EXISTS.
update b
set match = 1
from #b b
where exists
(
select b.keyword
from #a a
where a.keyword like b.keyword + '%'
)