sql查询更新表，其中缺少另一个表中的字段

Question

I have an issue with a SQL query/SP where I'm trying to update a table that has missing data in specific fields from another table where the data in those same fields exists and is valid. The trick here is I would like to anchor on a value in the first table. I can make it work with a INSERT INTO / SELECT FROM combo, but it creates a duplicate record.

Im using mysql 5.x. Here are the details. The table with missing data is thisweek and the table with valid data is lastweek . Field 1 is MACAddress (which exists and is the anchor) and exists in both tables (for ex. BE:EF:BA:BE:CA:FE), Fields 2-10 in thisweek are blank (''), but there is data in those same fields(Fields2-10) in table lastweek .

UPDATE thisweek
SET thisweek.field2 = lastweek.field2
where thisweek.MACAddress = lastweek.MACAddress and thisweek.filed2 = ''; 

I know that query isn't anywhere close, so looking for help. Again, the same MACAddress exists in both tables, with the only difference between tables being that field2 in thisweek is blank (and it shouldn't be) and needs to be equal to lastweek.field2 for that MACAddress .

Thanks all.

Answer 1

you need to JOIN thisweek and lastweek tables.

UPDATE thisweek
JOIN lastweek
ON thisweek.MACAddress = lastweek.MACAddress
AND thisweek.field2 =''
SET thisweek.field2 = lastweek.field2

Answer 2

I think you want the following:

UPDATE tw 
  SET tw.Field2 = lw.Field2
FROM
  ThisWeek tw 
  JOIN LastWeek lw ON tw.MACAddress = lw.MACAddress
WHERE
  tw.Field2 = ''

Answer 3

update table1 
inner join table2 on table1.id = table2.id and (table1.name = '' or table1.name is null) 
set table1.name = table2.name;