Question

I have a situation where a user may or may not provide various bits of data that need to go into a row containing that user’s info. The issue is that they need to make multiple entries into the row, over time, and I don’t want to null out any pre-existing values, if those had been set in the past.

My desire is to do something that looks (in pseudo code) like this:

var a,b,c;// these are the values that the user provides any of which may be null at any time

update user if a != null set name = a,  if b != null set phone = b, if c != null set email c

I’ve been trying to fashion an IF to work in this manner but I get syntax errors with the various ways I’ve tried. Hoping someone can shed light on the right way to do this (if it’s possible).

TIA

Answer 1

One way to do this is to “default” each column to its original value with COALESCE().

UPDATE user
SET name = COALESCE(a, name),
    phone = COALESCE(b, phone),
    email = COALESCE(c, email)
WHERE ...

COALESCE() returns its first non-null argument, so if a is null, it’ll just return the original value of name, so there will be no net change.

MySQL also supports a function ISNULL() which works like COALESCE(), but COALESCE() is standard SQL. Also, COALESCE() supports more than two arguments.