mysql query to select data from table2 which does not exist in table1

Question

I have 2 tables table1 and table2 , where table1 contains the data collected so far, and table2 contains table1 's data along with some updated/additional data. I need to retrieve only this updated/additional data and insert it into table1 .

Now I know I can use NOT IN to do this, but I am not sure it will be a very efficient solution in case of a huge number of records. Any suggestion on what the best approach would be in terms of execution speed?

Answer 1

This can be done with simple join both tables

something like below:

select t1.* from table1 as t1 join table2 as t2 on t1.id=t2.id where ...[]

Answer 2

I'm not sure if i've understand your question correctly but let me give it a try. Suppose you have a design like this:

TableA : {colA, colB, colC, colD, colE}
TableB : {colA, colB, RecC, RecD, RecE}

where Tables ( tableA , tableB ) is joined on ColA . I Assumed that TableA 's columns ( colC , ColD , colE ) will be updated and the records are based on TableB 's columns ( recC , recD , recE ).

In your statement: I need to retrieve only this updated/additional data and insert it into table1. . I think you want to update TableA 's records based on TableB

UPDATE TableA a INNER JOIN TableB b ON a.ColA = b.ColA
SET    a.ColC = b.RecC,
       a.ColD = b.RecD,
       a.ColE = b.RecE
-- WHERE (Condition)          -- if you want to have a condition.

so the statement above updates all the records in tableA if colA also exist in tableB since I've used INNER JOIN . You could also use LEFT JOIN .