SQL - PostgreSQL - Replace NULLs

Source: sql-snippets/replace-null.md at main · count/sql-snippets (github.com)

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Description

An essential part of cleaning a new data source is deciding how to treat NULL values.

The PostgreSQL function COALESCE can help with replacing NULL values with something else:

with data as (
  select * from (values
    (1,    'one'),
    (null, 'two'),
    (3,    null)
  ) as data (num, str)
)

select
  coalesce(num, -1) num,
  coalesce(str, 'I AM NULL') str
from data

Output:

num	str
1	a
-1	b
3	I AM NULL

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