Cross-table UPDATE in SQLITE3

Question

In SQL Server, I can do something like this:

UPDATE tbl1 
   SET col2 = tbl2.col2 
  FROM table1 tbl1 
 INNER JOIN table2 tbl2 
    ON tbl1.col1 = tbl2.col1

I haven't bothered to look whether this is part of any SQL standard or not, and I'm sure there are other ways to do it, but it is astoundingly useful.

Here's my problem. I need to do something similar in SQL (i.e, not a host language) with SQLITE3. Can it be done?

Answer 1

Since version 3.33, SQLite supports the UPDATE FROM idiom, however in a slightly different flavour than that of SQL Server: the target table must not be listed in the FROM cause, meaning that joins with it must be done in a WHERE clause.

Your example becomes:

UPDATE tbl1 
   SET col2 = tbl2.col2 
  FROM tbl2
 WHERE tbl1.col1 = tbl2.col1

Answer 2

This works for sqlite:

UPDATE tbl1 SET col2 = (SELECT col2 FROM tbl2 WHERE tbl2.col1 = tbl1.col1)

Answer 3

Just to emphasize Geogory Higley's post:

I have had problems with UPDATE tbl1 SET col2 = (SELECT col2 FROM tbl2 WHERE tbl2.col1 = tbl1.col1) where it updates columns in tbl1 that do not exist in tbl2.

see cheetah post at http://sqlite.phxsoftware.com/forums/p/1708/7238.aspx which points to:

http://www.mail-archive.com/[email protected]/msg27207.html

The code is:

insert or replace into foo (id, name, extra)
select bar.id, bar.name, foo.extra
  from bar 
  left join foo 
    on bar.id = foo.id;

and this seems to work correctly. There seem to be many posts at different sites that recommend the first approach so it is a bit confusing. I would suggest you test your output very carefully if you use this method which does seem faster and may work with matched tables.

Answer 4

I've discovered this can be done with INSERT OR REPLACE INTO. A little more verbose than T-SQL's equivalent, but just as handy.