suppose I have a sql like this:
select * from tba
if table tba have data, it will be shown like below:
id name num
1 tom 100
2 jack 200
now i need query tba by where conditon
select num from tba where id = 3;
here is the question: there's no data anymore by this sql, will be like this:
id name num
//no data, just have column name
so, i want to it tell me that there's no result or only zero, like:
num
0
how can i get the result?
Thanks!!
Try this:
SELECT COALESCE(MAX(num), 0) AS num
FROM tba
WHERE id = 3
If you wanted to select all columns, you can do:
SELECT COALESCE(MAX(id), 0) AS id,
COALESCE(MAX(name), 'N/A') AS name,
COALESCE(MAX(num), 0) AS num
FROM tba
WHERE id = 3;
SELECT ISNULL(num,0) AS num
FROM tba
WHERE id = 3
ISNULL is not supported by PostgreSQL. 2) ISNULL in MySQL returns only either 0 or 1. 3) Without wrapping the num column in an aggregate function, you would return no results even if you made a conditional check on it.