根据表1中的条件将SQL更新表（1）转换为另一个表中的值

Question

I'm trying to create a sort of conversion tool that will update a set of data with new values based on certain conditions.

Table A has columns Scheme1, Class1, Condition 1, Condition 2,

Table B has a list of all possible Scheme(s)2, Class(s)2 that I need to update to.

Basically, everything in Table A sets the conditions for what needs to be updated. Which is where I'm having difficulty.

I was planning something along the lines of

UPDATE table_A
SET class1 = table_B.class '1'
WHERE IN (class1= '1', condition1 = '1', condition2 = '2')

then repeating this for all classifications. There's about 50 classifications.

Is this on the right track, or is there a quicker/cleaner way to do this? Do I even need the second table or can I just update it in line? Would it be easier to just create a 3rd instead of updating the original table? (I need to move this data outside of SQL after the conversion)

Answer 1

If I understand you correctly, this should work

UPDATE a
SET class1 = b.class
FROM
    TableA a
    JOIN TableB b ON a.scheme = b.scheme
WHERE
    a.condition1=...
    AND a.condition2 = ...

Answer 2

Approach the development of UPDATE statements from a SELECT first perspective, then once you can retrieve the values the way you want them, convert the select into an UPDATE.

First build a SELECT to visualize the results. Update what with what with what .

SELECT a.class1
       b.class1
FROM table_A AS a
  INNER JOIN table_B AS b
    ON a.id = b.id
WHERE a.condition1 = '1'

Now you can modify that to an UPDATE.

--SELECT a.class1
--       b.class1
UPDATE a
SET a.class1 = b.class1
FROM table_A AS a
  INNER JOIN table_B AS b
    ON a.id = b.id
WHERE a.condition1 = '1'