update using self join not returning the results I am looking for

Question

Hi all I need to do a self join that doesn't include the null value.

Create the table:

 CREATE TABLE t2 ( col1 varchar(255), col2 varchar(255), col3 varchar(255), col4 varchar(255), col5 varchar(255), col6 varchar(255) ); --Populate the table: INSERT INTO t1 (col1, col2, col3, col4, col5, col6) VALUES ('1', '', 'new1', 'name1','',''), ('2', '', 'new2', 'name2','oldvalue1',''), ('3', '', 'new3', 'name3','',''), ('4', 'value1', 'new4', 'name4','','') ; --Resulting in: | col1 | col2 | col3 | col4 | col5 | col6 | | 1 | | new1 | name1 | | | | 2 | | new1 | name1 | oldvalue1 | | | 3 | | new1 | name1 | | | | 4 | value1 | new1 | name1 | | | 

My update:

update t2 AS A, t2 AS B
set A.col6 = B.col3
where B.col5 = A.col2;

But the result is:

  | col1 | col2 | col3 | col4 | col5 | col6 | | 1 | | new1 | name1 | | new1 | | 2 | | new1 | name1 | oldvalue1 | new1 | | 3 | | new1 | name1 | | new1 | | 4 | value1 | new1 | name1 | | | 

What I want is:

 | col1 | col2 | col3 | col4 | col5 | col6 | | 1 | | new1 | name1 | | | | 2 | | new1 | name1 | oldvalue1 | new1 | | 3 | | new1 | name1 | | | | 4 | value1 | new1 | name1 | | | 

what am I doing wrong?

I am using myspql and sequelpro on a mac

Thanks!

Answer 1

did you try that ?

update b set b.col6=a.col3 from t2 a inner join t2 b on b.col5 = a.col2

Answer 2

thanks for all the help. I figured out what my issue was. in the table the null cess were just blank they didn't contain "NULL" in them. once i updated the table to have "NULL" in the blank cells then everything worked. thanks again for helping me on my sql journey.