I realize that this has probably been asked a billion times, and I could swear I've done this in the past, but tonight I've got brain block or something and can't figure it out...
I have a database table ("t1") where I need to be able to retrieve only the first row where a particular value appears in a particular column.
Here's a sample of the data:
id | qID | Name
---------------------
1 | 1 | Bob
2 | 3 | Fred
3 | 1 | George
4 | 1 | Jack
What I want as a result is:
id | qID | Name
---------------------
1 | 1 | Bob
2 | 3 | Fred
The only column I actually need to get out of the query is the first one, but that's not where the duplicates need to be eliminated, and I thought it might be confusing not to show the entire row.
I've tried using this:
select id, qID, ROW_NUMBER() over(partition by qID order by qID) as zxy
from t1 where zxy = 1
But it gives me this error:
Msg 207, Level 16, State 1, Line 14
Invalid column name 'zxy'.
If I remove the where part of the query, the rest of it works fine. I've tried different variable names, using single or double quotes around 'zxy' but it seems to make no difference. And try as I might, I can't find the part of the SQL Server documentation where it discusses assigning a variable name to an expression, as in the "as zxy" part of the above query... if anybody has a link for that, that's quite useful.
Needless to say, I've tried other variable names besides "zxy" but that makes no difference.
Help!
WHERE clause is applied earlier in the process than SELECT. Therefore the calculated column zxy is not available in WHERE. In order to achieve your goal you need to put your original query in a subquery or CTE.
select id, qid
from
(
select id, qID, ROW_NUMBER() over(partition by qID order by qID) as zxy
from t1
) q
where zxy = 1
Output:
| id | qid |
|----|-----|
| 1 | 1 |
| 2 | 3 |
Here is SQLFiddle demo
Logical Processing Order of the SELECT statement
1 FROM
2 ON
3 JOIN
4 WHERE
5 GROUP BY
6 WITH CUBE or WITH ROLLUP
7 HAVING
8 SELECT
9 DISTINCT
10 ORDER BY
11 TOP
Where Clause Execute Before Select Clause so You can not find ZXY in Where cluase
with cte as
(
select id, qID, ROW_NUMBER() over(partition by qID order by qID) as zxy
from t1
)
select * from cte where zxy = 1
Here is my blog it might help you http://sqlearth.blogspot.in/2015/05/how-sql-select-statement-logically-works.html
Related
I have a table like so:
id | value
---+------
1 | 10
2 | 5
3 | 11
4 | 8
5 | 9
6 | 7
The data in this table is really pairs of values, which I need to take the average of, which should result in:
pair_id | pair_avg
--------+---------
1 | 7.5
2 | 9.5
3 | 8
I have got some other information (a pair of flags) which could also help to pair them, though they still have to be in id order. I cannot really change how the data comes to me.
As I'm more used to arrays than SQL, all I can think is that I need to loop through the table and sum the pairs. But this doesn't strike me as very SQL-ish.
Update
In making this minimal example, I have apparently over simplified.
As the table I am working with is the result of several selects, the IDs will not be quite so clean, apologies for not specifying this.
The table looks a lot more like:
id | value
----------
1 | 10
4 | 5
6 | 11
7 | 8
10 | 9
15 | 7
The results will be used to create a second table, I don't care about the index on this new table, it can provide its own, therefore giving the result already indicated above.
If your data is as clean as the question makes it seem: no NULL values, no gaps, pairs have consecutive positive numbers, starting with 1, and assuming id is type integer, it can be as simple as:
SELECT (id+1)/2 AS pair_id, avg(value) AS pair_avg
FROM tbl
GROUP BY 1
ORDER BY 1;
Integer division truncates the result and thus takes care of grouping pairs automatically this way.
If your id numbers are not as regular but at least strictly monotonically increasing like your update suggests (still no NULL or missing values), you can use a surrogate ID generated with row_number() instead:
SELECT id/2 AS pair_id, avg(value) AS pair_avg
FROM (SELECT row_number() OVER (ORDER BY id) + 1 AS id, value FROM tbl) t
GROUP BY 1
ORDER BY 1;
db<>fiddle here
I think you can just use group by with arithmetic:
select row_number() over (order by min(id)), min(id), max(id), avg(id)
from t
group by floor( (id - 1) / 2 );
I'm not sure why you would want to renumber the ids after aggregation. The original ids seem more useful.
You may use ceil function by appliying division by 2 to id column as in the following select statement :
with t(id,value) as
(
select 1 , 10 union all
select 2 , 5 union all
select 3 , 11 union all
select 4 , 8 union all
select 5 , 9 union all
select 6 , 7
)
select ceil(id/2::numeric) as "ID", avg(t.value) as "pair_avg"
from t
group by "ID"
order by "ID";
id | pair_avg
-------------
1 | 7.5
2 | 9.5
3 | 8
I'm trying to query for records that share common relationships. In order to avoid gratuitous context, here is a hypothetical example from my favorite old-school Nintendo game:
Consider a table of boxers:
tableBoxers
ID | boxerName
----------------
1 | Little Mac
2 | King Hippo
3 | Von Kaiser
4 | Don Flamenco
5 | Bald Bull
Now I have a relationship table that links them together
boxingMatches
boxerID1 | boxerID2
-----------------------
1 | 3
2 | 5
2 | 4
5 | 1
4 | 1
Since I don't want to discriminate between ID1 and ID2, I create a query that UNIONs them together:
SELECT firstID AS boxerID1, secondID AS boxerID2 FROM
(
SELECT boxerID1 AS firstID, boxerID2 AS boxerID FROM boxingMatches
UNION ALL
SELECT boxerID2 AS firstID, boxerID1 AS secondID FROM boxingMatches
) ORDER BY firstID, secondID
I get:
queryBoxingMatches
boxerID1 | boxerID2
-----------------------
1 | 3
1 | 4
1 | 5
2 | 4
2 | 5
3 | 1
4 | 1
4 | 2
5 | 1
5 | 2
Now I have VBA script where a user can select the boxers he's interested in. Let's say he selects Little Mac (1) and King Hippo (2). This gets appended into a temporary table:
summaryRequest
boxerID
--------
1
2
Using table [summaryRequest] and [queryBoxingMatches], how do I find out whom Little Mac (1) and King Hippo (2) have similarly fought against? The result should be Bald Bull (5) and Don Flamenco (4).
Bear in mind that [summaryRequest] could have 0 or more records. I have considered an INTERSECT, but I'm not sure that's the right function for this. I've tried using COUNT numerous ways, but it gives undesired data when there are multiple relationships (e.g. if Little Mac fought Bald Bull twice and King Hippo only fought him once).
I can't help but feel like the answer is plain and simple and I'm just overthinking it. Any help is appreciated. Thanks.
Not sure if that works like this in MS Access:
SELECT boxerID2, COUNT(*) as cnt
FROM queryBoxingMatches
WHERE boxerID1 IN (SELECT boxerID FROM summaryRequest)
GROUP BY boxerID2
HAVING COUNT(DISTINCT boxerID1) = (SELECT COUNT(DISTINCT boxerID)
FROM summaryRequest)
Okay, I think I found the answer:
SELECT boxerID2 FROM
(
SELECT boxerID2, COUNT(boxerID2) AS getCount FROM queryBoxingMatches
WHERE boxerID1 IN (SELECT ID FROM summaryRequest)
GROUP BY boxerID2
)
WHERE getCount = (SELECT COUNT(*) FROM summaryRequest)
It's a play off of COUNT(), which I don't like because COUNT() doesn't guarantee a full-fledged relationship--just a pattern.
I have an SQL table with one bit column. If only one bit value (in my case 1) occurs in the rows of the table, how can I make a SELECT statement which shows for, example, the occurance of both bit values in the table, even if the other does not occur? This is the result I'm trying to achieve:
+----------+--------+
| IsItTrue | AMOUNT |
+----------+--------+
| 1 | 12 |
| 0 | NULL |
+----------+--------+
I already tried to google the answer but without success, as English is not my native language and I am not that familiar with SQL jargon.
select IsItTrue, count(id) as Amount from
(select IsItTrue, id from table
union
select 1 as IsItTrue, null as id
union
select 0 as IsItTrue, null as id) t
group by bool
I want my query to return the rows of a table in groups where a column contains specific values. After I got the rows ordered in the groups I want to be able to order them by name.
Example Table
- Id - Name - Group
- 1 George Group_2_1
- 2 Alfred Group_2_2
- 3 Eric Group_3
- 4 Mary Group_1_2
- 5 Jon Group_1_1
I want them ordered by their group and after that ordered by their name
- Id - Name - Group
- 1 Jon Group_1_1
- 2 Mary Group_1_2
- 3 Alfred Group_2_2
- 4 George Group_2_1
- 5 Eric Group_3
I found this SQL-Query-Snippet
ORDER BY CASE WHEN Group LIKE '%Group_1%' THEN 1 ELSE 2 END, Group
but it is not enough. The result is only grouped by the first group (obviously) but I can't extend it to order the second group because it is in the same column.
Please don't get confused by the example.
I just want to be able to group certain rows and put them in front of the results. I want a result that has all rows containing group 1 in the top, containing group 2 in the middle and containing group 3 in the bottom.
The values are not "Group_1_1" or something like that. They are just some strings and I want certain strings to be always in the first row (group 1) and some always below group 1
The problem here seems to be that some of your group names have an extra underscore, otherwise you could just order by the Group and all would be good. You could probably do something like this to work around this?
WITH Data AS (
SELECT 'Group1_1' AS Value
UNION
SELECT 'Group_3_2' AS Value
UNION
SELECT 'Group_2_2' AS Value
UNION
SELECT 'Group_3_1' AS Value
)
SELECT * FROM Data ORDER BY CASE WHEN Value LIKE 'Group_%' THEN SUBSTRING(Value, 7, 10) ELSE SUBSTRING(Value, 6, 10) END;
Results:
Value
Group1_1
Group_2_2
Group_3_1
Group_3_2
---- EDIT ----
Okay, seeing as your example isn't really an "example" it sounds like you are going to need a really, REALLY long case statement. You could do something like this (using the original Group_1_1, Group_2_2 codes) that would extend to different values. The key is that a CASE statement works from left to right and a value is assigned to the first case that matches:
ORDER BY
CASE
WHEN [Group] = 'Group_1_1' THEN 1
WHEN [Group] = 'Group_1_2' THEN 2
WHEN [Group] LIKE 'Group_1_%' THEN 3
WHEN [Group] = 'Group_2_1' THEN 4
WHEN [Group] = 'Group_2_2' THEN 5
WHEN [Group] LIKE 'Group_2_%' THEN 6
etc.
END;
Obviously that's very generic and depends on what the actual values are in your database.
Edits for mssql
If there is ANY instance of 3 underscores then the following simply won't work. However if there is the possibility of Group_12_6 or Group_21_1 then this approach may be worth trying.
It removes Group_ or Group from the string, leaving 1_1 or 12_6 or 21_1 then it replaces the remaining underscore with . giving 1.1 or 12.6 or 21.1 and casts this to decimal.
All utterly dependent of the consistency of those group names.
SELECT
id
, name
, [Group]
FROM YourData
ORDER BY
CAST(REPLACE(REPLACE(REPLACE([Group], 'Group_', ''), 'Group', ''), '_', '.') AS decimal(12,3))
, name
I'm really hoping you do not have a column called [Group] but if you do it has to be referenced as [Group] or "Group". Test result:
| ID | NAME | GROUP |
|----|--------|-----------|
| 1 | Jon | Group_1_1 |
| 2 | Mary | Group_1_2 |
| 4 | George | Group_2_1 |
| 3 | Alfred | Group_2_2 |
| 5 | Eric | Group_3 |
see http://sqlfiddle.com/#!3/e95b07/1
this is actually a sorting question almost solved thanks to other posts I've found here on StackOverflow.
basically i'm trying to bumb a row up , no need to insert it somewhere in the middle of the table and change all the following rows id's just one place up (replace order id's with previous).
I've found a solution for this in another post WHEN the id's are known for example.
ID | name | surname
1 | John | doe
2 | Jane | Dane
but my table has gaps and often its more like
ID | name | surname
2 | John | doe
7 | Jane | Dane
So i can't really rely on subtracting the id by 1 and replacing row 7 with the row number 7-1.
Is it somehow possible to swwitch the row id X with the one before without knowing the other id ?
is it possible to do it SQL only ? i have an idea of php-ing it but it seems alot like a fix not a solution.
This would work in SQL Server, I'm assuming in MySQL too:
SELECT *
FROM MyTable MT
...
WHERE ID = (SELECT MAX(ID) FROM MyTable MT2 WHERE ID < MT.ID)