I'm creating an empty column in my table, when I use '' as columnname, it created empty column but String type. How can I create empty column but Integer/decimal type?
Null as columnname doesn't work!
Thank you!
Adding an INT column with NULLs inside a SELECT query:
SELECT
CAST(NULL AS INT) AS columnname
check this snippet which creates a new empty column of INT datatype
ALTER TABLE schema.tablename ADD column_a INT NULL ;
You can create empty column of integer type and null is not a string value:
SELECT
hat,
shoe,
boat,
0 as placeholder for number
FROM table
And '' as placeholder for strings.
And null as placeholder for null 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 am reading a flat file in hive and i have null values coming in file like below
a|b|null|null|d
and when I create table on top of this with below datatypes
a char(1),b char(1),c char(1),varchar2(2),char(1)
and the value in table coming like this
a,b,n,nu,d
The oneway I can do this is to make the datatype as varchar2(4) and add check at null.
But is there any other way i can do this.
SerDe treats 'null' strings as normal values, no difference between value 'a' and 'null'.
Try to add 'serialization.null.format'='null' property to your table definition:
ALTER TABLE mytable SET tblproperties('serialization.null.format'='null');
Another approach is to use STRING data type and case statements is select:
select case when col = 'null' then null end as col
...
Looking at a column that holds last 4 of someone's SSN and the column was originally created as an int datatype. Now SSN that begin with 0 get registered as 0 on the database.
How can I convert the column and it's information from an int into a string for future proof?
You should convert. CONVERT(VARCHAR(4), your_col)
If you specifically want zero-padded numbers, then the simplest solution is format():
select format(123, '0000')
If you want to fix the table, then do:
alter table t alter column ssn4 char(4); -- there are always four digits
Then update the value to get the leading zeros:
update t
ssn4 = format(convert(int, ssn4), '0000');
Or, if you just want downstream users to have the string, you can use a computed column:
alter table t
add ssn4_str as (format(ssn4, '0000'));
If you want to add leading zeros, use:
SELECT RIGHT('0000'+ISNULL(SSN,''),4)
First thing never store SSN or Zip Code as any numeric type.
Second you should fix the underlying table structure not rely on a conversion...but if you're in a jam this is an example of a case statement that will help you.
IF OBJECT_ID('tempdb..#t') IS NOT NULL
BEGIN
DROP TABLE #t
END
GO
CREATE TABLE #t(
LastFourSSN INT
)
INSERT INTO #t(LastFourSSN)
VALUES('0123'),('1234')
SELECT LastFourSSN --strips leading zero
FROM #t
SELECT -- adds leading zero to anything less than four charaters
CASE
WHEN LEN(LastFourSSN) < 4
THEN '0' + CAST(LastFourSSN AS VARCHAR(3))
ELSE CAST(LastFourSSN AS VARCHAR(4))
END LastFourSSN
FROM #t
If you are looking for converting values in the column for your purpose to use in application, you can use this following-
SELECT CAST(your_column AS VARCHAR(100))
--VARCHAR length based on your data
But if you are looking for change data type of your database column directly, you can try this-
ALTER TABLE TableName
ALTER COLUMN your_column VARCHAR(200) NULL
--NULL or NOT NULL based on the data already stored in database
As in title. I have one column which has some text values. For example column data1 has values ('31',32','',NULL). Now I want to update another column say data2 (type INT) with data from data1, so I am trying to do something like that:
UPDATE table SET data2=CAST(data1 AS INT).
The problem is because PostgreSQL cannot cast NULL or empty values to INT.
Actually, you can cast NULL to int, you just can't cast an empty string to int. Assuming you want NULL in the new column if data1 contains an empty string or NULL, you can do something like this:
UPDATE table SET data2 = cast(nullif(data1, '') AS int);
If you want some other logic, you can use for example (empty string converts to -1):
UPDATE table SET data2 = CASE WHEN data1 = '' THEN -1 ELSE cast(data1 AS int) END;
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