根据来自另一个表的联接更新MySQL NULL值

Question

I have two tables, one Master and one ExtraData. Both tables share columns FirstName, LastName, Gender and A_Id .

The query I am working on should compare the two tables and UPDATE any NULL values for A_Id in Master using A_Id in Extra.

What is the best way to do this? I could compare CONCAT(FirstName, LastName, Gender) but I'm stuck on how to update the column based on a JOIN .

Answer 1

You can use many criteria in a join, and then simply set a column in one source table to the value of a column in the other table:

UPDATE Master 
JOIN ExtraData 
  ON Master.FirstName = ExtraData.FirstName
  AND Master.LastName = ExtraData.LastName
  AND Master.Gender = ExtraData.Gender
SET Master.A_Id = ExtraData.A_Id 
WHERE Master.A_Id IS NULL

Note that the JOIN condition can be made more succinct (because the columns are named the same): JOIN ExtraData USING (FirstName, LastName, Gender)