I have a SQL table with a datetime field. The field in question can be null. I have a query and I want the results sorted ascendingly by the datetime field, however I want rows where the datetime field is null at the end of the list, not at the beginning.
Is there a simple way to accomplish that?
select MyDate
from MyTable
order by case when MyDate is null then 1 else 0 end, MyDate
(A "bit" late, but this hasn't been mentioned at all)
You didn't specify your DBMS.
In standard SQL (and most modern DBMS like Oracle, PostgreSQL, DB2, Firebird, Apache Derby, HSQLDB and H2) you can specify NULLS LAST or NULLS FIRST:
Use NULLS LAST to sort them to the end:
select *
from some_table
order by some_column DESC NULLS LAST
I also just stumbled across this and the following seems to do the trick for me, on MySQL and PostgreSQL:
ORDER BY date IS NULL, date DESC
as found at https://stackoverflow.com/a/7055259/496209
If your engine allows ORDER BY x IS NULL, x or ORDER BY x NULLS LAST use that. But if it doesn't these might help:
If you're sorting by a numeric type you can do this: (Borrowing the schema from another answer.)
SELECT *
FROM Employees
ORDER BY ISNULL(DepartmentId*0,1), DepartmentId;
Any non-null number becomes 0, and nulls become 1, which sorts nulls last because 0 < 1.
You can also do this for strings:
SELECT *
FROM Employees
ORDER BY ISNULL(LEFT(LastName,0),'a'), LastName
Any non-null string becomes '', and nulls become 'a', which sorts nulls last because '' < 'a'.
This even works with dates by coercing to a nullable int and using the method for ints above:
SELECT *
FROM Employees
ORDER BY ISNULL(CONVERT(INT, HireDate)*0, 1), HireDate
(Lets pretend the schema has HireDate.)
These methods avoid the issue of having to come up with or manage a "maximum" value of every type or fix queries if the data type (and the maximum) changes (both issues that other ISNULL solutions suffer). Plus they're much shorter than a CASE.
You can use the built-in function to check for null or not null, as below. I test it and its working fine.
select MyDate from MyTable order by ISNULL(MyDate,1) DESC, MyDate ASC;
order by coalesce(date-time-field,large date in future)
When your order column is numeric (like a rank) you can multiply it by -1 and then order descending. It will keep the order you're expecing but put NULL last.
select *
from table
order by -rank desc
In Oracle, you can use NULLS FIRST or NULLS LAST: specifies that NULL values should be returned before / after non-NULL values:
ORDER BY { column-Name | [ ASC | DESC ] | [ NULLS FIRST | NULLS LAST ] }
For example:
ORDER BY date DESC NULLS LAST
Ref: http://docs.oracle.com/javadb/10.8.3.0/ref/rrefsqlj13658.html
If you're using MariaDB, they mention the following in the NULL Values
documentation.
Ordering
When you order by a field that may contain NULL values, any NULLs are
considered to have the lowest value. So ordering in DESC order will see the
NULLs appearing last. To force NULLs to be regarded as highest values, one can
add another column which has a higher value when the main field is NULL.
Example:
SELECT col1 FROM tab ORDER BY ISNULL(col1), col1;
Descending order, with NULLs first:
SELECT col1 FROM tab ORDER BY IF(col1 IS NULL, 0, 1), col1 DESC;
All NULL values are also regarded as equivalent for the purposes of the
DISTINCT and GROUP BY clauses.
The above shows two ways to order by NULL values, you can combine these with the
ASC and DESC keywords as well. For example the other way to get the NULL values
first would be:
SELECT col1 FROM tab ORDER BY ISNULL(col1) DESC, col1;
-- ^^^^
SELECT *
FROM Employees
ORDER BY ISNULL(DepartmentId, 99999);
See this blog post.
Thanks RedFilter for providing excellent solution to the bugging issue of sorting nullable datetime field.
I am using SQL Server database for my project.
Changing the datetime null value to '1' does solves the problem of sorting for datetime datatype column. However if we have column with other than datetime datatype then it fails to handle.
To handle a varchar column sort, I tried using 'ZZZZZZZ' as I knew the column does not have values beginning with 'Z'. It worked as expected.
On the same lines, I used max values +1 for int and other data types to get the sort as expected. This also gave me the results as were required.
However, it would always be ideal to get something easier in the database engine itself that could do something like:
Order by Col1 Asc Nulls Last, Col2 Asc Nulls First
As mentioned in the answer provided by a_horse_with_no_name.
Solution using the "case" is universal, but then do not use the indexes.
order by case when MyDate is null then 1 else 0 end, MyDate
In my case, I needed performance.
SELECT smoneCol1,someCol2
FROM someSch.someTab
WHERE someCol2 = 2101 and ( someCol1 IS NULL )
UNION
SELECT smoneCol1,someCol2
FROM someSch.someTab
WHERE someCol2 = 2101 and ( someCol1 IS NOT NULL)
USE NVL function
select * from MyTable order by NVL(MyDate, to_date('1-1-1','DD-MM-YYYY'))
Here's the alternative of NVL in most famous DBMS
order by -cast([nativeDateModify] as bigint) desc
Related
I have to sort one column of mytable in ascending order but problem is mytable contains some special characters related data. Still I want to sort in ascending order so that it display in proper manner in UI.
Can anyone help me with this?
I have tried using
ORDER BY Item DESC
But it gives me first ABC type rows then {ABC} type rows.Means giving special characters in last
You can try this for your problem :
select * from mytable ORDER BY REGEXP_REPLACE(Item,'[^[:alnum:]'' '']', NULL) DESC
I have this table:
How can I get the MAX date for each ID from each row?
Use Greatest
SELECT id, GREATEST (date1, date2, date3)
FROM YourTable
Note that GREATEST and LEAST are not in the SQL standard, but are a common extension. Some other databases make them return NULL if any argument is NULL, rather than only when all are NULL.
It seems that order by with nulls doesn't really work for jsonb?
if I have many rows in a table that look like this:
key | cae1f6e1-8c1b-4fec-9002-7fd878e0dc06
value | {"id": "cae1f6e1-8c1b-4fec-9002-7fd878e0dc06",
"debit-amount": 207853501,
"credit-amount": null}
and when I run query like this:
select value->'debit-amount' deb from balance_table
order by deb asc
nulls last
limit 20;
it still shows only nulls
You can cast 'null'::jsonb to null with nullif():
select nullif(value->'debit-amount', 'null') deb
from balance_table
order by deb asc nulls last
limit 20;
The problem with your query is in the following part:
order by deb asc
nulls last
limit 20;
You would assume that this sorts all rows in a way that the ones that have null for debit-amount will end up in the end, so that when to do limit 20 you will probably see only non null ones. There is only one issue, the jsonb null is not the same as the sql null.
For example, suppose that a particular row has a value with "debit-amount": null. Then value->'debit-amount' will return a jsonb null, which will get sorted to the top, because that's how the order in jsonb works. In other words, you'll never get a sql null (unless of course the whole value is sql null), so the nulls last is pointless here.
You probably want something like that:
select value->'debit-amount' deb
from balance_table
order by ((value->'debit-amount')='null'::jsonb)::integer, deb asc
limit 20;
The expression ((value->'debit-amount')='null'::jsonb)::integer will convert all (jsonb) nulls for debit-amount to 1 and will return 0 otherwise. This will push all (jsonb) nulls to the end.
In this data - there are multiple DATA_ID values associated with time-series data. I am trying to exclude all data from any DATA_ID values that return a NULL value for USE for any timestamp value.
In other words, I only want to return DATA_ID values (and their data) if they have complete (not any NULL) values for all timestamp values.
Sample query given below:
SELECT
My.Table.DATA_ID,
MY.Table.timestamp,
My.Table.USE
FROM
My.TABLE
WHERE timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59'
-- Something here that says exclude all data from DATA_ID(s)
-- with any missing USE data, i.e. USE=NULL
ORDER BY DATA_ID, timestamp
Assuming I understand your question correctly and you want to exclude whole batches of samples (determined by equal data_id and timestamp) that contain a null value.
SELECT
My.Table.DATA_ID,
MY.Table.timestamp,
My.Table.USE
FROM
My.TABLE o
WHERE timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59'
and not exists (select 1 from my_table i
where i.use is null
and i.data_id = o.data_id
and i.timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59')
ORDER BY DATA_ID, timestamp
The simple thing to do is something like this:
CREATE FUNCTION missing_info(MY.TABLE)
RETURNS BOOL
LANGUAGE SQL AS
$$ select $1.use is null -- chain conditions together with or.
-- no from clause needed. no where clause needed.
$$;
Then you can just add:
where (My.Table).missing_info is not true;
And as you need to change the logic as to what sorts of info is missing you can just change it in the function and everything still works.
This is the sort of encapsulation of derived information where ORDBMS's like PostgreSQL really shine.
Edit: Re-reading your example, it looks like what you are looking for is the IS NULL operator. However if you need to re-use some sort of logic, see the above example. NULL never "equals" NULL (because we can't say whether two unknown values are the same). But IS NULL tells you whether it is NULL or not.
i have image table, which has 2 or more rows with same date.. now im tring to do order by created_date DESC, which works fine and shows rows same position, but when i change the query and try again, it shows different positions.. and no i dont have any other order by field, so im bit confused on why its doing it and how can i fix it.
can you please help on this.
To get reproducible results you need to have columns in your order by clause that together are unique. Do you have an ID column? You can use that to tie-break:
ORDER BY created_date DESC, id
I suspect that this is happening because MySQL is not given any ordering information other than ORDER BY created_date DESC, so it does whatever is most convenient for MySQL depending on its complicated inner workings (caching, indexing, etc.). Assuming you have a unique key id, you could do:
SELECT * FROM table t ORDER BY t.created_date DESC, t.id ASC
Which would give you the same result every time because putting a comma in the arguments following ORDER BY gives it a secondary ordering rule that is executed when the first ordering rule doesn't produce a clear order between two rows.
To have consistent results, you will need to add at least more column to the 'ORDER BY' clause. Since the values in the created_date column are not unique, there is not a defined order. If you wanted that column to be 'unique', you could define it as a timestamp.