In BIDS, I'm running a Data Flow Task & I'm wondering what the difference is behind the scenes between using "Table or view" vs "SQL Command" for the Data Access Mode for an OLE DB Source. For example, suppose I have a table called mytable with 5 columns (column1, column2, column3, column4, column5) but I'm only interested in column1. I see these 2 options:
- I can either use "Table or view" and select "mytable" and then only check "column 1" from the "Columns" pane.
- Or I can use "SQL Command" and use this query "select column1 from mytable".
When I ran a test, the second option seemed to run much faster but I'd like confirmation of what's going on behind-the-scenes when I use "Table or view" and then only select certain columns. I'd appreciate any insight anyone can provide.
(In my particular use case, mytable is an offsite Azure Database table and column2 has large amounts of xml within it. My guess is that all of the columns were coming over the wire when I used "Table or view")