I have this table (made from a SQL query):
Row 1 Row 2
2 1
3 NULL
And I want to minus the 2 columns, so I just select like this:
Select Row1 - Row2
From table
But then I get this result:
1
NULL
instead of:
1
3
How can I make it possible to get the last result?
Please try:
SELECT ISNULL([Row 1], 0) - ISNULL([Row 2], 0) from YourTable
For more Information visit ISNULL
The reason you got this is because Any Mathematical operation with NULL produces NULL So while doing operation all values should be read as NULL=0.
With ISNULL()
Hence
SELECT ISNULL([Row 1], 0) - ISNULL([Row 2], 0) from YourTable
The MySQL equivalent of ISNULL is IFNULL
If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns
expr2.
Maybe also look at SQL NULL Functions
The ISNULL from MySQL is used to check if a value is null
If expr is NULL, ISNULL() returns 1, otherwise it returns 0.
in sql anything minus with NULL then it is always NULL so you need to convert NULL to Zero
SELECT ISNULL(ROW1,0)-ISNULL(ROW2,0) FROM YOUR_TABLE
Select Row1 - COALESCE(Row2,0)
From table
Related
I have a table TEST_TABLE as follows:
Name x_col y_col
=======================
Jay NULL 2
This is a simplistic representation of a much larger issue but will suffice.
When I do the following query I get NULL returned
SELECT SUM(x_col + y_col) FROM TEST_TABLE WHERE Name='Jay'
I want it to be 2. I thought the SUM() method ignores NULL values. How can I ignore values that are null in this query? Or actually in general, as this is a problem for a lot of my algorithms.
You get NULL because NULL + 2 returns NULL. The SUM() has only one row, and if the + expression is NULL, then the SUM() returns NULL.
If you want NULL to be treated as 0, the use COALESCE():
SELECT SUM(COALESCE(x_col, 0) + COALESCE(y_col, 0))
FROM TEST_TABLE
WHERE Name = 'Jay';
One final note. If you start with your data and filtered out all rows, then the result will still be NULL. To get 0, you need an additional COALESCE():
SELECT COALESCE(SUM(COALESCE(x_col, 0) + COALESCE(y_col, 0)), 0)
FROM TEST_TABLE
WHERE Name = 'Jayden';
Use COALESCE to replace NULL with 0.
SELECT sum(coalesce(x_col, 0) + coalesce(y_col, 0)) FROM TEST_TABLE WHERE Name='Jay'
i get confused in learning coalesce, I am new to sql.
example :
select case when value is null then 1
else value end as value
from table
and
select coalesce(value, 1)
from table
and in the tutorial I see in internet there are like
select coalesce (arg_1, arg_2, arg_3)
if I make
select coalesce(value, 1, 2)
how I can make to show the return value is 2?
Your query with the first and second will reproduce the same result, But you are wrong understanding the Coalesce concept.
Definition in Documentation Postgresql
The COALESCE function returns the first of its arguments that is not
null. Null is returned only if all arguments are null.
So it means it will return the first argument that is not null, it is not like case statement with condition like true or false
Let's try with example :
select coalesce(null, 1)
It will return 1 like the query you show, or
select coalesce(null, null, 1)
It will return 1 too even 1 in the arg_3 and how about there are 2 value not null?
select coalesce(null, 1, 2)
It will return 1. Why? Like in the documentation said "returns the first of its arguments that is not null" so when there is 2 value not null the first argument have not null value will get return
You can check this demo and try :
Demo<>Fiddle
Hope it helps
I am using Postgres and have the following SQL statement:
SELECT *
FROM "osmlocal-dsd-de".t_osm_vehicle_image t
WHERE t.vehicle_config_id = 3
and image_type_id = 2
Which returns one row:
id vehicle_config_id cosy_url image_type_id
113 3 SomeValue 2
When I run the following:
SELECT * from "osmlocal-dsd-de".t_osm_vehicle_image t
WHERE t.vehicle_config_id = 3
and image_type_id = 2
and coalesce(t.cosy_url, '') = ''
Zero rows are returned.
I think my understanding of coalesce is wrong, because I would have expected one row still to be returned, because the cosy_url is not null.
Any advise on what I am doing wrong would be appreciated.
Your understanding of coalesce is wrong
It returns the first argument that is not null. If all arguments are null, the COALESCE function will return null
In your case t.cosy_url is not null it is equally SomeValue and your condition doesn't work because SomeValue is not equal ''
You seem to be misunderstanding coalesce(). It returns the first value that is not null.
In your case, you have:
coalesce(t.cosy_url, '')
Because t.cosy_url has a value ('SomeValue'), this evaluates to that value. The value is not '' so the expression returns false and the entire where clause returns false.
If you want non-NULL values, then use:
t.cosy_url is not null
I try to select max value from table
SELECT MAX(cid) FROM itemconfiguration;
However when table itemconfiguration is empty the MAX(cid) statements is evaluated to NULL while i need a number. How to handle this and treat NULL as 0 ?
Just use Coalesce or NVL to handle NULLs.
The following code will return 0 if MAX(cid) is NULL
SELECT COALESCE(MAX(cid), 0)
FROM itemconfiguration
SELECT NVL(MAX(cid), 0) FROM itemconfiguration;
Can replace a number when max return null using ISNULL ,
ISNULL(MAX(cid),0) FROM itemconfiguration;
How can I return 1 if the SQL below returns NULL?
Something like (pseudo code):
if sql return NULL value
then set value to one
otherwise returning sql result value.
Is there any SQL for defining default value to 1 if SQL result is NULL?
SELECT Max(iCategoryOrder)+1
FROM [IVRFlowManager].[dbo].[tblCategory]
WHERE iCategoryLevel = 1
Option 1
Use ISNULL()
Description
Replaces NULL with the specified replacement value.
SELECT MAX(ISNULL(iCategoryOrder, 0))+1
FROM [IVRFlowManager].[dbo].[tblCategory]
WHERE iCategoryLevel = 1
Option 2
Use COALESCE()
SELECT MAX(COALESCE(iCategoryOrder, 0))+1
FROM [IVRFlowManager].[dbo].[tblCategory]
WHERE iCategoryLevel = 1
Description
Returns the first nonnull expression among its arguments.
Use ISNULL operator like:
ISNULL(your_field, 1)
Try following:
Select ISNULL(Max(iCategoryOrder), 0) + 1
from [IVRFlowManager].[dbo].[tblCategory]
where iCategoryLevel = 1