In SQL how do you update each row of the table by finding all rows that are equal for a column, then set another column equal to eachother

Question

So basically this would be the psuedo code, but I don't know how to do this in SQL, please help.

for each row in table1{
    loop through each row in table 2 {
        if table1's row.column 1 = table2's row.column 2 for this row {
            set table1's row.col2 = table2's row.col2
        }
    }
}

Edit: Okay let me be more specific. We are basically switching from hibernate sequence as ids to using guids for the id column. I'm trying to update the foreign keys associated by making a temp of the previous foreign key column and then matching the temporary columns to update the actual columns.

suppose table one had id's and table two had a column for those ids to use as foreign keys. I wanna use the previous values in table 2 to match with the rows in table 1 and set the key values in table 2 to match the new guid of table 1.

so table 2 may have multiple rows of duplicate id's but table 1 will never have duplicates. If that makes any sense.

Answer 1

In SQL Server you can do something like:

UPDATE Table_1
SET Column_2 = t2.Column_2
FROM Table_1 AS t1
INNER JOIN Table_2 AS t2 ON t2.Column_1 = t1.Column_1

or something like

UPDATE Table_1
SET Column_2 = ( 
    SELECT t2.Column_2
    FROM Table_2 AS t2
    WHERE t2.Column_1 = Table_1.Column_1
)

Of course if you have multiple rows in Table_2, you will get an error....