Question

This is probably a simple question, but I pretty new to this. I am trying to set a column in an sql server using the following command:

update myTable 
set myCol = a.col 
from table2 as a 
where a.col_1 = col_1 and a.col_2 = col_2;

myTable is a bout 150 million rows. and table2 about 300,000 rows. I have indexed table2 properly so the look up is fast. I tried this on a million row separately and it took around 20 secs. But the whole table is taking a very long time, over two days now, and still not finished. I wondered whether there is a better solution for this.

Thanks in advance.

Answer 1

I think the syntax of the UPDATE statement should be

UPDATE  b 
SET     b.myCol = a.col 
FROM    myTable b
        INNER JOIN table2 a
            ON  a.col_1 = b.col_1 AND
                a.col_2 = b.col_2

and you need to supply compound INDEX on (col_1, col_2) on both tables.