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
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 a problem with sorting in postgresql. The information must be sorted in descending order according to the first column, but in case of a tie, the information must be sorted in ascending order according to the second column.
How can I accomplish this ?
SELECT ... ORDER BY col1 DESC, col2 ASC
select *
from t
order by c1 desc, c2 asc
Of course.
http://www.postgresql.org/docs/9.2/static/sql-select.html#SQL-ORDERBY
The ORDER BY clause causes the result rows to be sorted according to the specified expression(s). If two rows are equal according to the leftmost expression, they are compared according to the next expression and so on.
and later
Optionally one can add the key word ASC (ascending) or DESC (descending) after any expression in the ORDER BY clause.
one more:
Note that ordering options apply only to the expression they follow; for example ORDER BY x, y DESC does not mean the same thing as ORDER BY x DESC, y DESC.
Emphasis, my own.
I know UNION removes duplicates but it changes result order even when there are no duplicates.
I have two select statements, no order by statement anywhere
I want union them with or without (all)
i.e.
SELECT A
UNION (all)
SELECT B
"Select B" actually contains nothing, no entry will be returned
if I use "Select A union Select B", the order of the result is different from just "Select A"
if I use:
SELECT A
UNION ALL
SELECT B
the order of the result is the same as "Select A" itself and there are no duplicates in "Select A" at all.
Why is this? it is unpredictable.
The only way to get a particular order of results from an SQL query is to use an ORDER BY clause. Anything else is just relying on coincidence and the particular (transitory) state of the server at the time you issue your query.
So if you want/need a particular order, use an ORDER BY.
As to why it changes the ordering of results - first, UNION (without ALL) guarantees to remove all duplicates from the result - not just duplicates arising from the different queries - so if the first query returns duplicate rows and the second query returns no rows, UNION still has to eliminate them.
One common, easy way to determine whether you have duplicates in a bag of results is to sort those results (in whatever sort order is most convenient to the system) - in this way, duplicates end up next to each other and so you can then just iterate over these sorted results and if(results[index] == results[index-1]) skip;.
So, you'll commonly find that the results of a UNION (without ALL) query have been sorted - in some arbitrary order. But, to re-emphasise the original point, what ordering was applied is not defined, and certainly shouldn't be relied upon - any patches to the software, changes in indexes or statistics may result in the system choosing a different sort order the next time the query is executed - unless there's an ORDER BY clause.
One of the most important points to understand about SQL is that a table has no guaranteed order, because a table is supposed to represent a set (or multiset if it has duplicates), and a set has no order. This means that when you query a table without specifying an ORDER BY clause, the query returns a table result, and SQL Server is free to return the rows in the output in any order. If the results happen to be ordered, it may be due to optimization reasons. The point I'm trying to make is that any order of the rows in the output is considered valid, and no specific order is guaranteed. The only way for you to guarantee that the rows in the result are sorted is to explicitly specify an ORDER BY clause.
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.