Updating only the rows matched by field value from CROSS JOIN of 2 tables (SQL)

Here's what needs to be done: Match 2 fields from different tables in SQL Server( done ), update fields in table1 where table1.field1 = table2.field2 (problem, it just updates all the records in the table)

Here's what I have , where tempTableName is a table imported to SQL Server for the purpose of the query:

"UPDATE Table1 SET Table1.fieldN ='" + DateTime.Now.DayOfYear + "' FROM " + tempTableName + " CROSS JOIN Table1 WHERE (" + tempTableName + ".fieldX = Table1.fieldY)"

Her开发者_开发百科e's what I've figured out:

everything after the FROM is useless as far as actual functionality is concerned, it runs the query but the results are not "linked" in any way to the actual UPDATE statement

To sum up :

The query I've figured out updates all records in table1, I need the query to update only the rows matched by the query after FROM

PS. Forgive me if this seems trivial and that I haven't done research but the fact of the matter is that 2 weeks ago I'd never even heard of SQL and have relied heavily on SO for direction and advice.

Your CROSS JOIN should be an INNER JOIN instead.

"UPDATE t1
    SET fieldN ='" + DateTime.Now.DayOfYear + "' 
    FROM " + tempTableName + " t2 INNER JOIN Table1 t1 ON t1.fieldy = t2.fieldx"