Question

I’ve got two tables:

Table 1 = idhash - username - usermail
Table 2 = idhash - views    - fistseen - lastseen

Now I want to merge these tables to a new table:

Table 3 = idhash - username - usermail - firstseen - lastseen

*notice that I want to drop the views column.

I’ve tried with solutions that I found on google, but so far they do not seem to work.

• Not all the idhash columns from table 2 have a corresponding idhash in table 1. Stiil store those ‘mismatched’ rows with empty username and usermail

Answer 1

This query will give you the results:

SELECT A.*, B.firstseen, B.lastseen
FROM [Table 1] A
LEFT JOIN [Table 2] B
ON A.idhash = B.idhash

And to insert and update the results on your [Table 3]:

INSERT INTO [Table 3](idhash, username, usermail, firstseen, lastseen)
SELECT A.*, B.firstseen, B.lastseen
FROM [Table 1] A
LEFT JOIN [Table 2] B
ON A.idhash = B.idhash
LEFT JOIN [Table 3] C
ON A.idhash = C.idhash
WHERE C.idhash IS NULL

-- For SQL Server
UPDATE T3
SET firstseen = T1.firstseen,
    lastseen = T1.lastseen
FROM [Table 3] T3
INNER JOIN (SELECT A.*, B.firstseen, B.lastseen
            FROM [Table 1] A
            LEFT JOIN [Table 2] B
            ON A.idhash = B.idhash) T1
WHERE T3.firstseen != T1.firstseen OR T3.lastseen != T1.lastseen