Is it harmful to update columns which aren't changed?

by Katrin   Last Updated September 25, 2018 21:06 PM

Say I have a table with some columns:

CREATE TABLE t
(
    key int PRIMARY KEY,
    c1  int,
    c2  text,
    c3  timestamptz
);

I now fetch a row from the table:

SELECT * FROM t WHERE id = 180;

In my application, I now only change the value of one column, let's say c2. Is it harmful performance-wise to do:

UPDATE t
SET    t1 = <exact the same value as before>,
       t2 = <new value>,
       t3 = <exact the same value as before>
WHERE  key = 180;

instead of:

UPDATE t
SET    t2 = <new value>
WHERE  key = 180;

?



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