MySQL IF NOT NULL, then display 1, else display 0

mysql if-statement

coffeemonitor · Feb 22, 2012 · Viewed 347.5k times · Source

I'm working with a little display complication here. I'm sure there's an IF/ELSE capability I'm just overlooking.

I have 2 tables I'm querying (customers, addresses). The first has the main record, but the second may or may not have a record to LEFT JOIN to.

I want to display a zero if there is no record in the addresses table. And I want to only display 1, if a record exists.

What I've attempted so far:

SELECT c.name, COALESCE(a.addressid,0) AS addressexists
FROM customers c
LEFT JOIN addresses a ON c.customerid = a.customerid
WHERE customerid = 123

This first example does not do it. But I may be utilizing COALESCE wrong.

How can I display a 0, if null, and a 1, if something exists?

Answer

Instead of COALESCE(a.addressid,0) AS addressexists, use CASE:

CASE WHEN a.addressid IS NOT NULL 
       THEN 1
       ELSE 0
END AS addressexists

or the simpler:

(a.addressid IS NOT NULL) AS addressexists

This works because TRUE is displayed as 1 in MySQL and FALSE as 0.