In MS SQL-Server, I can do:
SELECT ISNULL(Field,'Empty') from Table
But in PostgreSQL I get a syntax error. How do I emulate the ISNULL() functionality ?
SELECT CASE WHEN field IS NULL THEN 'Empty' ELSE field END AS field_alias
Or more idiomatic:
SELECT coalesce(field, 'Empty') AS field_alias
Use COALESCE() instead:
SELECT COALESCE(Field,'Empty') from Table;
It functions much like ISNULL, although provides more functionality. Coalesce will return the first non null value in the list. Thus:
SELECT COALESCE(null, null, 5);
returns 5, while
SELECT COALESCE(null, 2, 5);
returns 2
Coalesce will take a large number of arguments. There is no documented maximum. I tested it will 100 arguments and it succeeded. This should be plenty for the vast majority of situations.
How do I emulate the ISNULL() functionality ?
SELECT (Field IS NULL) FROM ...
Try:
SELECT COALESCE(NULLIF(field, ''), another_field) FROM table_name
Related
I am new to SQL Server, and I want to validate whether a column value is NULL or empty in the select statement .
The select statement is :
SELECT COM_TYPE, COM_IN_CHARGE_POSITION
FROM TABLE_01
If the COM_TYPE value is null or empty, I want to take the COM_TYPE_OTHERS value as COM_TYPE for the same way to COM_IN_CHARGE_POSITION.
It's simply if the COM_TYPE and COM_IN_CHARGE_POSITION is null or empty I want to take the values from other two columns.
Can anyone help me to solve this?
Let me assume that blank is NULL. In that case, you simply want coalesce():
select coalesce(COM_TYPE, COM_TYPE_OTHERS, COM_IN_CHARGE_POSITION, COM_IN_CHARGE_POSITION_OTHERS) as effective_COM_TYPE
The coalesce() function takes the first non-NULL argument. If the values could be empty strings or strings with spaces in addition to NULL, then a case expression is recommended.
COALESCE function can check which one column is first non-NULL, but you, if you want to check, is null or empty you can try to use CASE WHEN
SELECT CASE WHEN COM_TYPE IS NULL OR COM_TYPE = '' THEN COM_TYPE_OTHERS
ELSE COM_TYPE END AS COM_TYPE,
CASE WHEN COM_IN_CHARGE_POSITION IS NULL OR COM_IN_CHARGE_POSITION = '' THEN COM_IN_CHARGE_POSITION_OTHERS
ELSE COM_IN_CHARGE_POSITION END AS COM_IN_CHARGE_POSITION,
FROM TABLE_01
Simplest way to check for null or empty is to use ISNULL and NULLIF :
SELECT ISNULL(NULLIF(COM_TYPE, ''), COM_TYPE_OTHERS)
FROM TABLE_01
You can also use COALESCE but it does not check for empty string (only null), so you will still have to use NULLIF.
Also note that ISNULL is faster than COALESCE even if the difference is pretty negligible.
You can use COALESCE() or ISNULL() OR CASE WHEN statement
SELECT COALESCE( COM_TYPE, COM_TYPE_OTHERS ) AS COM_TYPE,
COALESCE (COM_IN_CHARGE_POSITION , COM_IN_CHARGE_POSITION_OTHERS) AS COM_IN_CHARGE_POSITION
FROM TABLE_01
SELECT column_name1,column_name2,column_name3,column_name4 from table_name
How do i do multiple checks for all the coulmn_name?
for now i am checking for NULL to return "Empty String" using COALESCE.
SELECT
COALESCE(column_name1,'')as Column_name1,
COALESCE(column_name2,'')as Column_name2,
COALESCE(column_name3,'')as Column_name3,
COALESCE(column_name4,'')as Column_name4, from table_name
My requirement is to return "Empty String" where ever the values are NULL or WhiteSpaces or NA.
Thanks in advance.
One method uses case:
select (case when column_name1 is null or ltrim(rtrim(column_name1)) in ('NA', '') then ''
else column_name1
end)
CASE, ISNULL, COALESCE can all be used in combination as necessary.
If you are using the 2012 or later versions of SQL Server, there are 2 more options to choose from to simplify CASE statement:
1. IIF
2. CHOOSE
Check this link for more details
SELECT coalesce (nullif (rtrim(ltrim(column_name1)), 'N/A'), '')
AS column_name1
FROM table_name
Found an answer.. is this correct way?? i mean does this works exactly to the requirement?
Many times I have to run this query:
select * from users where name is not null and name != ''
Is there any better way to do this. I need more performance, any suggestion. I guess this is very common, so there may be some compiled function which will be something like
select * from users where name is present()
Using PostgreSQL 9 version.
For any x, null != x will be null and null is not true. That means that you can simply ignore NULLs in your case and say:
select * from users where name != ''
You could also convert NULLs to empty strings using COALESCE if that's clearer to you:
select * from users where coalesce(name, '') != ''
Of course that coalesce call isn't free.
Demo: http://sqlfiddle.com/#!2/e810c/2
You can use NULLIF:
SELECT *
FROM USERS
WHERE NULLIF(NAME,'') IS NOT NULL
There is a VARCHAR2 type column in my database table for store invoice_number. and there is a query to get max invoice_number as below.
select max(invoice_number) from invoice;
but there are no data in invoice table, above query return value as null. but in this case i need to replace this value to 0 instead of null. how could i do this ?
Using NVL:
SELECT NVL(MAX(invoice_number), '0')
Using the ANSI COALESCE:
SELECT COALESCE(MAX(invoice_number), '0')
Using DECODE:
SELECT DECODE(MAX(invoice_number), NULL, '0')
Using the ANSI CASE:
SELECT CASE
WHEN MAX(invoice_number) IS NULL THEN '0'
ELSE MAX(invoice_number)
END
Verdict
All work, I'd probably use NVL because COALESCE is ANSI but not known to necessarily work as fast as native alternatives.
You could use COALESCE
For instance:
select COALESCE(max(invoice_number),'0') from invoice;
select coalesce(max(invoice_number),0)
can also use Decode.
select decode(max(invoice_number),null, 0)
i need such query
select * from t where
field=ifnull(:param, field) 'it not work's
so if param=NULL i have
select * from t where field is NULL
but if param =4
i have
select * from t where field=4
You can use the case when in where clause AFAIK bot not sure about MySQl,
But the better approach is to translate them,
you can read about that SQL WHERE clauses: Avoid CASE, use Boolean logic
So
select * from t where (:param is null and filed is null) or (filed = :param)
You can try this alternative
this might help you
select * from t where (field = NULL AND param= NULL) OR field ='4'
When working with NULL you cannot use arithmetic operators. Try COALESCE to make a logical if with values integer or NULL
mysql> SELECT COALESCE(NULL,1);
-> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
-> NULL
I think you are looking for NULLIF instead of ifnull
I think better approach would be to use CASE in where clause in your case.