Compare 2 table columns and update new column - sql

Question

I have 2 tables like this:
For example in first row from table 2 col value is 3661 and its equal to 'med' from table 1 I want to update class from table 1 with 'MED' and ...
This is the code I wrote but something is wrong :(
UPDATE table1 SET
class = ( CASE
WHEN table2.col = table1.med
THEN 'MED'
--------------------------------
WHEN table2.col = table1.mgl
THEN 'MGL'
--------------------------------
WHEN table2.col = table1.rhp
THEN 'RHP'
--------------------------------
WHEN table2.col = table1.epd
THEN 'EPD'
--------------------------------
WHEN table2.col = table1.jpa
THEN 'JPA'
--------------------------------
ELSE 'NULL'
FROM
table1 LEFT outer JOIN table2
)

Answer 1

I edited your code. you did not mention which database you use,
Anyway try this:
UPDATE table1
SET class = ( CASE
WHEN table2.col = table1.med
THEN 'MED'
--------------------------------
WHEN table2.col = table1.mgl
THEN 'MGL'
--------------------------------
WHEN table2.col = table1.rhp
THEN 'RHP'
--------------------------------
WHEN table2.col = table1.epd
THEN 'EPD'
--------------------------------
WHEN table2.col = table1.jpa
THEN 'JPA'
--------------------------------
ELSE 'NULL'
END)
from table1 left join table2 on table1.number=table2.number

Answer 2

You want something like this:
UPDATE table1
SET class = COALESCE((SELECT MIN(CASE WHEN table2.col = table1.med THEN 'MED'
WHEN table2.col = table1.mgl THEN 'MGL'
. . .
END) as newval
FROM table2
), 'NULL')
This is a bit tricky. You need to decide which row you want if there are multiple matches. The above chooses an arbitrary value among the matches.
The coalesce() is to handle the case where there are no matches. The subquery will return NULL in that case.
This is standard SQL and should work in any database. Specific databases might have other ways of writing this query.

Answer 3

Tried it in MySQL, this is working
UPDATE Table1
INNER JOIN Table1 T1
LEFT JOIN Table2 T2
ON T1.number = T2.number
set T1.class =
( CASE
WHEN T2.col = T1.med
THEN 'MED'
WHEN T2.col = T1.mgl
THEN 'MGL'
WHEN T2.col = T1.rhp
THEN 'RHP'
WHEN T2.col = T1.epd
THEN 'EPD'
WHEN T2.col = T1.jpa
THEN 'JPA'
ELSE 'NULL'
END
)
EDIT:
In case of MS SQL SERVER, you can use this
UPDATE Table1
set class =
( CASE
WHEN T2.col = T1.med
THEN 'MED'
WHEN T2.col = T1.mgl
THEN 'MGL'
WHEN T2.col = T1.rhp
THEN 'RHP'
WHEN T2.col = T1.epd
THEN 'EPD'
WHEN T2.col = T1.jpa
THEN 'JPA'
ELSE 'NULL'
END
)
FROM Table1 T1
LEFT JOIN Table2 T2
ON T1.number = T2.number