CODEWITHSUNDEEP
sqldatabasepostgresqlnullcoalesce
ronan
ronan

Reputation: 4672

Using COALESCE to handle NULL values in PostgreSQL

I have the following query 

SELECT  DISTINCT 
     pt.incentive_marketing, 
     pt.incentive_channel, 
     pt.incentive_advertising 
FROM test.pricing pt 
WHERE pt.contract_id = 90000 
group by 1,2,3 
order by pt.incentive_marketing;

The above query returns the o/p as shown in the attached image enter image description here

However I want to replace all null values by 0 using COALESCE Please let me know how this can be achieved in above SELECT query

Now I further modified the query using coalesce as below

SELECT  
     COALESCE( pt.incentive_marketing, '0' ), 
     COALESCE(pt.incentive_channel,'0'), 
     COALESCE( pt.incentive_advertising,'0') 
FROM test.pricing pt 
WHERE pt.contract_id = 90000 
group by 1,2,3

the result of which is as attached in image 2.

I still receive one row with blank values

Upvotes: 75

Views: 139392

Answers (2)

Andrea Ligios
Andrea Ligios

Reputation: 50203

You can use COALESCE in conjunction with NULLIF for a short, efficient solution:

COALESCE( NULLIF(yourField,'') , '0' )

The NULLIF function will return null if yourField is equal to the second value ('' in the example), making the COALESCE function fully working on all cases:

                 QUERY                     |                RESULT 
---------------------------------------------------------------------------------
SELECT COALESCE(NULLIF(null  ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF(''    ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF('foo' ,''),'0')     |                 'foo'

Upvotes: 173

Evan Carroll
Evan Carroll

Reputation: 1

If you're using 0 and an empty string '' and null to designate undefined you've got a data problem. Just update the columns and fix your schema.

UPDATE pt.incentive_channel
SET   pt.incentive_marketing = NULL
WHERE pt.incentive_marketing = '';

UPDATE pt.incentive_channel
SET   pt.incentive_advertising = NULL
WHERE pt.incentive_marketing = '';

UPDATE pt.incentive_channel
SET   pt.incentive_channel = NULL
WHERE pt.incentive_marketing = '';

This will make joining and selecting substantially easier moving forward.

Upvotes: 8

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