Have you ever faced a problem while using SQL Query in your software where you have to replace the blank or null field in database table with “0” or “1” but you are unable to use “If condition” in the sql?
Here I have got a solution where you can replace or fill the blank or null table data with “0” or “1” by using COALESCE in SQL query.
Let us assume we have a table called “ITEM” and it has four fields named “ order_no”, “item_no”, “qty” and “style_sample_no” . In the field “style_sample_no” there is no data i.e. this filed is blank/null or empty.
Check the image (“style_sample_no” is empty)
So, if you want to implement the condition “ If style_sample_no==null then replace style_sample_no with 0 i.e. style_sample_no=0 ” you can do it easily with SQL Query without any IF Condition.
Here is the Solution (Check the image below)
By using COALESCE(i.style_sample_no,0) you can easily replace the blank field of style_sample_no of ITEM table with 0’s or “1”s without using any IF condition in the SQL query.
select i.order_no,i.item_no,i.qty, COALESCE(i.style_sample_no,0)as sample from item i
How To : Postgre SQL Issues about using COALESCE function
All About Basic 
COALESCE – it’s just alias to CASE, and CASE is alias for IF ELSE-IF ELSE so implicit you still use in conditional flows 🙂 The goal is do not use in flows, coz’ it reduce performance.
if you just need {0,1} or {true, false} try compare to NULL – it’s comparison and not conditional flows, i.e:
SELECT *,
aColumn is NULL — here no flows , i.e. IF (cond) so do this and this, ELSE do this
FROM aTable;
LikeLike