sql query distinct with Row_Number - sql

Question

I am fighting with the distinct keyword in sql.
I just want to display all row numbers of unique (distinct) values in a column & so I tried:
SELECT DISTINCT id, ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM table
WHERE fid = 64
however the below code giving me the distinct values:
SELECT distinct id FROM table WHERE fid = 64
but when tried it with Row_Number.
then it is not working.

Answer 1

This can be done very simple, you were pretty close already
SELECT distinct id, DENSE_RANK() OVER (ORDER BY id) AS RowNum
FROM table
WHERE fid = 64

Answer 2

Use this:
SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM
(SELECT DISTINCT id FROM table WHERE fid = 64) Base
and put the "output" of a query as the "input" of another.
Using CTE:
; WITH Base AS (
SELECT DISTINCT id FROM table WHERE fid = 64
)
SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM Base
The two queries should be equivalent.
Technically you could
SELECT DISTINCT id, ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS RowNum
FROM table
WHERE fid = 64
but if you increase the number of DISTINCT fields, you have to put all these fields in the PARTITION BY, so for example
SELECT DISTINCT id, description,
ROW_NUMBER() OVER (PARTITION BY id, description ORDER BY id) AS RowNum
FROM table
WHERE fid = 64
I even hope you comprehend that you are going against standard naming conventions here, id should probably be a primary key, so unique by definition, so a DISTINCT would be useless on it, unless you coupled the query with some JOINs/UNION ALL...

Answer 3

This article covers an interesting relationship between ROW_NUMBER() and DENSE_RANK() (the RANK() function is not treated specifically). When you need a generated ROW_NUMBER() on a SELECT DISTINCT statement, the ROW_NUMBER() will produce distinct values before they are removed by the DISTINCT keyword. E.g. this query
SELECT DISTINCT
v,
ROW_NUMBER() OVER (ORDER BY v) row_number
FROM t
ORDER BY v, row_number
... might produce this result (DISTINCT has no effect):
+---+------------+
| V | ROW_NUMBER |
+---+------------+
| a | 1 |
| a | 2 |
| a | 3 |
| b | 4 |
| c | 5 |
| c | 6 |
| d | 7 |
| e | 8 |
+---+------------+
Whereas this query:
SELECT DISTINCT
v,
DENSE_RANK() OVER (ORDER BY v) row_number
FROM t
ORDER BY v, row_number
... produces what you probably want in this case:
+---+------------+
| V | ROW_NUMBER |
+---+------------+
| a | 1 |
| b | 2 |
| c | 3 |
| d | 4 |
| e | 5 |
+---+------------+
Note that the ORDER BY clause of the DENSE_RANK() function will need all other columns from the SELECT DISTINCT clause to work properly.
All three functions in comparison
Using PostgreSQL / Sybase / SQL standard syntax (WINDOW clause):
SELECT
v,
ROW_NUMBER() OVER (window) row_number,
RANK() OVER (window) rank,
DENSE_RANK() OVER (window) dense_rank
FROM t
WINDOW window AS (ORDER BY v)
ORDER BY v
... you'll get:
+---+------------+------+------------+
| V | ROW_NUMBER | RANK | DENSE_RANK |
+---+------------+------+------------+
| a | 1 | 1 | 1 |
| a | 2 | 1 | 1 |
| a | 3 | 1 | 1 |
| b | 4 | 4 | 2 |
| c | 5 | 5 | 3 |
| c | 6 | 5 | 3 |
| d | 7 | 7 | 4 |
| e | 8 | 8 | 5 |
+---+------------+------+------------+

Answer 4

Using DISTINCT causes issues as you add fields and it can also mask problems in your select. Use GROUP BY as an alternative like this:
SELECT id
,ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM table
where fid = 64
group by id
Then you can add other interesting information from your select like this:
,count(*) as thecount
or
,max(description) as description

Answer 5

How about something like
;WITH DistinctVals AS (
SELECT distinct id
FROM table
where fid = 64
)
SELECT id,
ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM DistinctVals
SQL Fiddle DEMO
You could also try
SELECT distinct id, DENSE_RANK() OVER (ORDER BY id) AS RowNum
FROM #mytable
where fid = 64
SQL Fiddle DEMO

Answer 6

Try this:
;WITH CTE AS (
SELECT DISTINCT id FROM table WHERE fid = 64
)
SELECT id, ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM cte
WHERE fid = 64

Answer 7

Try this
SELECT distinct id
FROM (SELECT id, ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM table
WHERE fid = 64) t
Or use RANK() instead of row number and select records DISTINCT rank
SELECT id
FROM (SELECT id, ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS RowNum
FROM table
WHERE fid = 64) t
WHERE t.RowNum=1
This also returns the distinct ids

Answer 8

Question is too old and my answer might not add much but here are my two cents for making query a little useful:
;WITH DistinctRecords AS (
SELECT DISTINCT [col1,col2,col3,..]
FROM tableName
where [my condition]
),
serialize AS (
SELECT
ROW_NUMBER() OVER (PARTITION BY [colNameAsNeeded] ORDER BY [colNameNeeded]) AS Sr,*
FROM DistinctRecords
)
SELECT * FROM serialize
Usefulness of using two cte's lies in the fact that now you can use serialized record much easily in your query and do count(*) etc very easily.
DistinctRecords will select all distinct records and serialize apply serial numbers to distinct records. after wards you can use final serialized result for your purposes without clutter.
Partition By might not be needed in most cases