I am writing a pgplsql function in which I have a variable var that could be NULL or valorized. In a later query I do:
SELECT * FROM table WHERE column = var
that, in case of a NULL var, becomes
SELECT * FROM table WHERE column = NULL
So the query fails with NULL, because, as PostgreSQL documentation says,
The null value represents an unknown value, and it is not known whether two unknown values are equal
I resolved it with a CASE statement:
SELECT * FROM table WHERE
( CASE WHEN var IS NULL THEN column IS NULL ELSE column = var END ) = TRUE
But I am unsure wether this is the best way to resolve the question... do you have any good alternative?
SELECT * FROM table WHERE column IS NOT DISTINCT FROM var
If var has a value of NULL, do you really only want to select records having a column value of NULL? Or would you want to treat it as a 'select all'/'do not restrict'?
If the latter applies, then an approach like this would work. (This is pseudocode as I am native to MSSQL.)
SELECT * FROM table WHERE
(var IS NULL AND column = column) OR column = var
Related
I have two tables one is (providerLoc) and another one is (tmpProviderLoc) I need to take three columns combination from tmpProviderLoc and need to check the records exist in ProviderLoc
Case 1 : If record exist in providerLoc i need to update another column(Npi) in providerLoc based on column (npi) in tmpProviderLoc
case 2 : if not exist i need to insert the values in providerLoc
for that I have written below query:
MERGE INTO [dbo].[ProviderLoc] AS PL
USING
(
select *
from (
select *,
row_number() over (partition by [Location_ID],[PProviderTaxID]
,[POBOXZIP] order by [Location_ID],[PProviderTaxID],[POBOXZIP]) as row_number
from [dbo].[TmpProviderLoc]
) as rows
where row_number = 1
) AS TPL
ON TPL.[Location_ID] = PL.[ecProviderID]
AND TPL.[PProviderTaxID] = PL.[TaxID]
AND TPL.[NPI] = PL.[NPI]
AND TPL.[POBOXZIP] = PL.[POBOXZIP]
WHEN MATCHED THEN
UPDATE SET PL.[NPI] = CASE
WHEN TPL.[NPI] = NULL THEN PL.[NPI]
ELSE TPL.[NPI]
END
WHEN NOT MATCHED THEN
INSERT (EcProviderID,TaxID,NPI,POBOXZIP,ProviderLocationStatusID,CreatedON)
VALUES (TPL.[Location_ID],TPL.[PProviderTaxID],TPL.[NPI]
,TPL.[POBOXZIP],1,GETDATE());
But I am failing in updating the NPI value -- if npi value is new in tmpProviderLoc it is not updating in ProviderLoc..
Could any one please look into this issue..
or any other way to go through this kind of checking
The equal symbol in this is incorrect: WHEN TPL.[NPI] = NULL THEN PL.[NPI]
Use IS NULL
WHEN TPL.[NPI] IS NULL THEN PL.[NPI]
NULLs are special. They are "indeterminate" so they cannot be equal or unequal to anything purely because they just cannot have any value "determined". NULLs are the absence of value and equal/unequal does not apply.
To discover if NULL exists use IS NULL - or - IS NOT NULL to discover if there is a non-null value.
Is there a variable in SQL that can be used to represent ALL the possible values of a field? Something like this pseudo-code
SELECT name FROM table WHERE id = *ALL_EXISTING_ID-s*
I want to return all rows in this case, but later when I do a search and need only one item I can simply replace that variable with the id I'm looking for, i.e.
SELECT name FROM table WHERE id = 1
The simplest way is to remove the WHERE clause. This will return all rows.
SELECT name FROM table
If you want some "magic" value you can use for the ID that you can use in your existing query and it will return all rows, I think you're out of luck.
Though you could use something like this:
SELECT name FROM table WHERE id = IFNULL(?, id)
If the value NULL is provided, all rows will be returned.
If you don't like NULL then try the following query, which will return all rows if the value -1 is provided:
SELECT name FROM table WHERE id = IFNULL(NULLIF(?, -1), id)
Another approach that achieves the same effect (but requires binding the id twice) is:
SELECT name FROM table WHERE (id = ? OR ? = -1)
How do I write a query that if one column value is not null then compare the value with the querystring, else do not compare the column value.
for example, I have a tbl1 with programs1 and programs2 two columns, the value in these two columns can be null or with value. I want to have the if statement that say
if programs1 is not null, programs1=#programs and
if programs2 is not null, programs2=#programs
my query is like this:
select * from tbl1 where
(programs1 is not null and programs1=#programs)
and
(program2 is not null and programs2=#programs)
but it didn't work the way I want. How do I write a correct query for this case? TIA.
I believe you're looking for COALESCE.
WHERE COALESCE(programs1, programs2) = #Programs
However, if you'd like to compare only if it has a value:
-- If the column is null, ignore it. If it has a value, then
-- check that value.
WHERE (programs1 IS NULL OR programs1 = #Programs)
AND (programs2 IS NULL OR programs2 = #Programs)
Also, I assume you mean sql-server since you reference asp.net
ISNULL(programs1,programs2) = #Programs
or
(programs1 is not null and #Programs = programs1) or (programs2 is not null and #Programs = programs2)
select *
from tbl1
where (programs1=#programs or programs1 is null)
and (programs2=#programs or programs2 is null)
How do you write a SELECT statement that only returns rows where the value for a certain column is null?
Do you mean something like:
SELECT COLUMN1, COLUMN2 FROM MY_TABLE WHERE COLUMN1 = 'Value' OR COLUMN1 IS NULL
?
I'm not sure if this answers your question, but using the IS NULL construct, you can test whether any given scalar expression is NULL:
SELECT * FROM customers WHERE first_name IS NULL
On MS SQL Server, the ISNULL() function returns the first argument if it's not NULL, otherwise it returns the second. You can effectively use this to make sure a query always yields a value instead of NULL, e.g.:
SELECT ISNULL(column1, 'No value found') FROM mytable WHERE column2 = 23
Other DBMSes have similar functionality available.
If you want to know whether a column can be null (i.e., is defined to be nullable), without querying for actual data, you should look into information_schema.
Use Is Null
select * from tblName where clmnName is null
You want to know if the column is null
select * from foo where bar is null
If you want to check for some value not equal to something and the column also contains null values you will not get the columns with null in it
does not work:
select * from foo where bar <> 'value'
does work:
select * from foo where bar <> 'value' or bar is null
in Oracle (don't know on other DBMS) some people use this
select * from foo where NVL(bar,'n/a') <> 'value'
if I read the answer from tdammers correctly then in MS SQL Server this is like that
select * from foo where ISNULL(bar,'n/a') <> 'value'
in my opinion it is a bit of a hack and the moment 'value' becomes a variable the statement tends to become buggy if the variable contains 'n/a'.
select Column from Table where Column is null;
select * from tableName where columnName is null
For some reasons IS NULL may not work with some column data type. I was in need to get all the employees that their English full name is missing, I've used:
SELECT emp_id, Full_Name_Ar, Full_Name_En
FROM employees
WHERE Full_Name_En = '' or Full_Name_En is null
I have a field in a table that is boolean, a range of records have no value (not true or false). How do I write my SQL statement to find these?
I have tried the following SQL statements without success:
1) SELECT * FROM table WHERE field = NULL
2) SELECT * FROM table WHERE field != TRUE AND field != FALSE
Any help would be greatly appreciated.
Many Thanks, Ben
In TSQL, you need to use IS rather than = when comparing with NULL:
SELECT * FROM table WHERE field IS NULL
Try
select * from table where field IS null
You want IS NULL I believe:
SELECT * FROM table WHERE field IS NULL