Conditional update across multiple fields - sql

Question

New to SQL so still learning all there is to offer.
I'm bringing in data from multiple sources and building a unique identifier table.
Several fields must be populated in order of precedence (i.e. the first datasource is preferred, then 2nd and so on).
Here is what I'm trying to do
UPDATE
TABLE1 AS DIMTABLE
SET
FIRSTNAME = ifnull( FIRSTNAME, RAWTABLE.FIRSTNAME )
, DIMTABLE.MIDDLENAME = ifnull( DIMTABLE.MIDDLENAME, RAWTABLE.MIDDLENAME )
, DIMTABLE.LASTNAME = ifnull( DIMTABLE.LASTNAME, RAWTABLE.LASTNAME )
, DIMTABLE.GENDER = IFNULL( DIMTABLE.GENDER, RAWTABLE.GENDER )
, DIMTABLE.DOB = IFNULL( DIMTABLE.DOB, RAWTABLE.DOB )
, DIMTABLE.PHONE1 = IFNULL( DIMTABLE.PHONE1, RAWTABLE.PHONE1 )
, DIMTABLE.PHONE2 = IFNULL( DIMTABLE.PHONE2, RAWTABLE.PHONE2 )
, DIMTABLE.EMAIL = IFNULL( DIMTABLE.EMAIL, RAWTABLE.EMAIL )
, DIMTABLE.FAX = IFNULL( DIMTABLE.FAX, RAWTABLE.FAX )
FROM
TABLE2 AS RAWTABLE
WHERE
RAWTABLE.ID_SOURCE_ID = 9
AND DIMTABLE.UID = RAWTABLE.UID
I have a sequence of these statements. One for each RAWTABLE.IDSOURCE_ID = 10,11,15...
The result is that the null fields I'm trying to update, remain null.
I was hoping something like this was possible to avoid multiple passes over the table.
I'm struggling with this approach which usually means there must be a better way

Answer 1

One option is to prepare rows first(giving preference first NOT NULL value in a column per UID):
CREATE OR REPLACE TEMPORARY TABLE RAWTABLE_SINGLE_UID
AS
SELECT DISTINCT
UID
,FIRST_VALUE(FIRSTNAME) IGNORE_NULLS
OVER(PARTITION BY UID ORDER BY SOURCE_ID) AS FIRSTNAME
,FIRST_VALUE(LASTNAME) IGNORE_NULLS
OVER(PARTITION BY UID ORDER BY SOURCE_ID) AS LASTNAME
,...
FROM TABLE2
WHERE SOURCE_ID IN (9,10,11,15);
Warning QUALIFY does not guarantee first non-null value per column but entire row:
CREATE OR REPLACE TEMPORARY TABLE RAWTABLE_SINGLE_UID
AS
SELECT *
FROM TABLE2
WHERE SOURCE_ID IN (9,10,11,15)
QUALIFY ROW_NUMBER() OVER(PARTITION BY UID ORDER BY SOURCE_ID) = 1
And then perform update:
UPDATE TABLE1 AS DIMTABLE
SET FIRSTNAME = ifnull( FIRSTNAME, RAWTABLE.FIRSTNAME )
, DIMTABLE.MIDDLENAME = ifnull( DIMTABLE.MIDDLENAME, RAWTABLE.MIDDLENAME )
, DIMTABLE.LASTNAME = ifnull( DIMTABLE.LASTNAME, RAWTABLE.LASTNAME )
, DIMTABLE.GENDER = IFNULL( DIMTABLE.GENDER, RAWTABLE.GENDER )
, DIMTABLE.DOB = IFNULL( DIMTABLE.DOB, RAWTABLE.DOB )
, DIMTABLE.PHONE1 = IFNULL( DIMTABLE.PHONE1, RAWTABLE.PHONE1 )
, DIMTABLE.PHONE2 = IFNULL( DIMTABLE.PHONE2, RAWTABLE.PHONE2 )
, DIMTABLE.EMAIL = IFNULL( DIMTABLE.EMAIL, RAWTABLE.EMAIL )
, DIMTABLE.FAX = IFNULL( DIMTABLE.FAX, RAWTABLE.FAX )
FROM RAWTABLE_SINGLE_UID AS RAWTABLE
WHERE DIMTABLE.UID = RAWTABLE.UID;

Answer 2

If I understand correctly, you can use LEFT JOIN for this purpose with `COALESCE:
UPDATE TABLE1 main
SET FIRSTNAME = COALESCE(T1.FIRSTNAME, t2.FIRSTNAME, t3.FIRSTNAME),
. . ..
FROM TABLE1 T1 LEFT JOIN
TABLE2 T2
ON T2.UID = T1.UID LEFT JOIN
TABLE3 t3
ON t3.UID = T1.UID
WHERE T1.ID_SOURCE_ID = 9 AND
T1.UID = MAIN.UID;
This is assuming the following:
You want to update ID_SOURCE_ID = 9 in the main table.
UID is a unique id in all the tables.
The secondary tables do not need to have all the UIDs.