I try to use stored procedure in my project.However i have question about null and empty.
ALTER PROCEDURE [dbo].[SP_EMAIL_LIST]
AS
BEGIN
SELECT *
FROM CUSTOMER
WHERE
EMAIL_ADRESS IS NOT NULL
END
I used where clause for avoid getting values null or empty values however i still get null values.
How can i get email adress values if not null and not empty ?
This should work.
SELECT
*
FROM
CUSTOMER
WHERE
EMAIL_ADRESS IS NOT NULL AND EMAIL_ADRESS != ''
Keep in mind there is a difference between NULL and ''. '' is simply an empty string. NULL generally is used to indicate an unknown or unspecified value.
Related
I am using Oracle DB. At the database level, when you set a column value to either NULL or '' (empty string), the fetched value is NULL in both cases. Is it possible to store '' (empty string) as a non NULL value in the database?
I execute this
UPDATE contacts SET last_name = '' WHERE id = '1001';
commit;
SELECT last_name, ID FROM contacts WHERE id ='1001';
LAST_NAME ID
------------ ------
null 1001
Is it possible to store the last_name as a non-NULL empty string ('')?
The only way to do this in oracle is with some kind of auxiliary flag field, that when set is supposed to represent the fact that the value should be an empty string.
As far as i know Oracle does not distinguish between '' and NULL, see here.
Oracle has a well know behavior that it silently converts "" to NULL on INSERT and UPDATE statements.
You have to deal with this in your code to prevent this behavior by converting NULL to "" when you read the columns back in and just do not use null in your program to begin with.
A long time since I used Oracle, but I believe we used to use a single space ' ' to represent an empty string, then trim it after reading.
If you use a VARCHAR2 data type then NULL and '' are identical and you cannot distinguish between them; so, as mentioned in other answers, you would either need to:
Have an additional column that contains a flag that distinguishes between non-NULL and NULL values so that if then flag states it is non-NULL and it contains a NULL then you know it is an empty string; or
Use an alternate representation, such as a single space character, for an empty string. This would then mean that you cannot store a string with that alternate representation; however, if trailing white-space was syntactically invalid for the strings you are storing then using a single space character to represent an empty string would be fine.
If you are using a CLOB data type then you CAN store an empty string using the EMPTY_CLOB() function:
CREATE TABLE table_name (value CLOB);
INSERT INTO table_name (value) VALUES (NULL);
INSERT INTO table_name (value) VALUES (EMPTY_CLOB());
INSERT INTO table_name (value) VALUES ('A');
Then:
SELECT value, LENGTH(value) FROM table_name;
Outputs:
VALUE
LENGTH(VALUE)
null
null
0
A
1
db<>fiddle here
I have a case statement to rectify one business logic in snowflake:
INSERT INTO DB.table_b
SELECT
CASE
WHEN UPPER(emp) <> LOWER(emp) THEN NULL
WHEN emp IS NULL THEN nullif(emp, 'NULL')
ELSE emp
END AS emp_no
FROM
DB.table_a;
The 'table_a' content as below :
emp
-------
ABCD
NULL
''
23
It contains character string, null, empty and numbers. So, the requirement is to take only numbers and empty values from the case statement since the column emp_no in 'table_b' is numeric type. In source table if the column value is string then we have to insert NULL value. But as the 'table_b' column is of type 'numeric' the null value is not getting inserted and getting following error
Numeric value '' is not recognized
Using TRY_TO_NUMBER:
A special version of TO_DECIMAL , TO_NUMBER , TO_NUMERIC that performs the same operation (i.e. converts an input expression to a fixed-point number), but with error-handling support (i.e. if the conversion cannot be performed, it returns a NULL value instead of raising an error).
INSERT INTO DB.table_b
SELECT TRY_TO_NUMBER(emp) AS emp
FROM DB.table_a;
you can not use IS_INTEGER but for VARCHAR(16777216) it isn't supported
So a regular expression would be better
INSERT INTO DB.table_b
SELECT
CASE
WHEN regexp_like(emp,'^[0-9]+$') THEN emp
ELSE NULL
END AS emp_no
FROM
DB.table_a;
As Lukasz mentions you should use the TRY_TO_x functions (TRY_TO_NUMERIC, TRY_TO_DOUBLE) as these safely handle parsing the types, and return NULL if the parse fails. The extra note I will add is that both NUMBER/NUMERICs and DOUBLEs will parse 0.1234 but get different results, which you didn't mention as caring about, but I think is worth noting, so I am adding an extra answer to point the difference out.
The CTE is just to get the values into the SQL:
WITH data(emp) as (
select * from values
('ABCD'),
(NULL),
(''),
('0.123'),
('23')
)
SELECT emp
,try_to_numeric(emp) as emp_as_num
,try_to_double(emp) as emp_as_float
FROM data
EMP
EMP_AS_NUM
EMP_AS_FLOAT
'ABCD'
null
null
null
null
null
''
null
null
'0.123'
0
0.123
'23'
23
23
You can test for amp being string and set the string to NULL. Only numeric values will go into the second case statement.
SELECT
CASE
WHEN IS_VARCHAR(emp) then NULL else
case WHEN UPPER(emp) <> LOWER(emp) THEN NULL ELSE emp end
end AS emp_no
I have a stored procedure that includes a table variable which updates from other table variables. ISNULL() is not working in the below code. It returns the proper value if there is something in TR.TotalRequestCnt, but NULL if there is no value in the TotalRequest table for this column.
UPDATE #OutputTable
SET TotalRequestCount = ISNULL(TR.TotalRequestCnt, 0)
FROM #TotalRequest TR
JOIN #OutputTable OT
ON TR.Document = OT.Document
Values of Document are identifying INTs (5577,5575, 5574).
#TotalRequest values are all INT:
5577 NULL NULL
5575 NULL NULL
5574 2 1
I have also tried using COALESCE() instead of ISNULL() to no success.
I found the answer.
No update is being performed in the row at all because there are no values so ISNULL never has the chance to fire.
I'm using C# to write to a SQL Compact Edition 3.5 database. I got a table containing e-mail addresses and names for each address.
MailRecipientAddressID int primary key identity(1,1) not null,
Address nvarchar(4000),
Name nvarchar(4000)
In this table I want every address-name combination to be unique. In some cases it's possible that either Address or Name is NULL in a row. Before inserting new rows into this table, I'm using a SELECT query to check if there is an existing row matching the one I want to insert. When using this query
SELECT MailRecipientAddressID FROM MailRecipientAddress WHERE Address = #Address AND Name = #Name
I will not find existing rows with NULL values in one column (see here).
Now I got this query, which works and kind of solves my problem
SELECT MailRecipientAddressID FROM MailRecipientAddress WHERE ISNULL(Address, '') = ISNULL(#Address, '') AND ISNULL(Name, '') = ISNULL(#Name, '')
but even though it is no problem in my case that NULL and empty string values are handled equally, I do not like this solution. I think it's kind of hackish. Is there a better approach
to apply a filter on a SELECT statement with parameters which can contain NULL
which works on SQL CE
Edit
I do not understand why, but my query works with SQL Management Studio but it does not in my application (see here). To correct my own approach I would need to use COALESCE.
I don't like the option to replace my NULL values with empty strings because I think it would be kind of inconsequent to set a value at a place where I got no value or is my understanding of this design question wrong?
The best solution is a constraint on the table that prevents duplicates from going into the table. You can put one in with a unique index:
create unique index idx_MailRecipientAddress_address_name on MailRecipientAddress(Address, Name);
This will generate an error on the insert, which you would then need to catch.
However, this is only a partial solution, because NULL values do not count as duplicates. You might solve your overall problem by not allowing NULL values in the field at all. Instead, represent no data using empty strings. Note: I wouldn't normally recommend this. In SQL, NULL means "unknown" and by the definition of the language, two "unknown" values are not equal. However, you seem to want them to be equal.
As for SQL, yours is okay, but it equates NULL and the empty string. An explicit check is more accurate:
WHERE (Address = #Address or Address is null and #Address is null) and
(Name = #Name or Name is null and #Name is null)
#George
if Parameter value is Null and column value is not null then "(Address = #Address or Address is NULL) returns false "
if Parameter value is Null and column value is null then "(Address = #Address or Address is NULL) returns true"
if Parameter value is Not Null and column value is null then "(Address = #Address or Address is NULL) returns true"
if Parameter value is Not Null and column value is Not null and if matches then "(Address = #Address or Address is NULL) returns true otherwise false"
SELECT MailRecipientAddressID FROM MailRecipientAddress WHERE (Address = #Address or Address is NULL) AND (Name = #Name or Name is NULL)
I am using Oracle DB. At the database level, when you set a column value to either NULL or '' (empty string), the fetched value is NULL in both cases. Is it possible to store '' (empty string) as a non NULL value in the database?
I execute this
UPDATE contacts SET last_name = '' WHERE id = '1001';
commit;
SELECT last_name, ID FROM contacts WHERE id ='1001';
LAST_NAME ID
------------ ------
null 1001
Is it possible to store the last_name as a non-NULL empty string ('')?
The only way to do this in oracle is with some kind of auxiliary flag field, that when set is supposed to represent the fact that the value should be an empty string.
As far as i know Oracle does not distinguish between '' and NULL, see here.
Oracle has a well know behavior that it silently converts "" to NULL on INSERT and UPDATE statements.
You have to deal with this in your code to prevent this behavior by converting NULL to "" when you read the columns back in and just do not use null in your program to begin with.
A long time since I used Oracle, but I believe we used to use a single space ' ' to represent an empty string, then trim it after reading.
If you use a VARCHAR2 data type then NULL and '' are identical and you cannot distinguish between them; so, as mentioned in other answers, you would either need to:
Have an additional column that contains a flag that distinguishes between non-NULL and NULL values so that if then flag states it is non-NULL and it contains a NULL then you know it is an empty string; or
Use an alternate representation, such as a single space character, for an empty string. This would then mean that you cannot store a string with that alternate representation; however, if trailing white-space was syntactically invalid for the strings you are storing then using a single space character to represent an empty string would be fine.
If you are using a CLOB data type then you CAN store an empty string using the EMPTY_CLOB() function:
CREATE TABLE table_name (value CLOB);
INSERT INTO table_name (value) VALUES (NULL);
INSERT INTO table_name (value) VALUES (EMPTY_CLOB());
INSERT INTO table_name (value) VALUES ('A');
Then:
SELECT value, LENGTH(value) FROM table_name;
Outputs:
VALUE
LENGTH(VALUE)
null
null
0
A
1
db<>fiddle here