I'm quite new into SQL and I'd like to make a SELECT statement to retrieve only the first row of a set base on a column value. I'll try to make it clearer with a table example.
Here is my table data :
chip_id | sample_id
-------------------
1 | 45
1 | 55
1 | 5986
2 | 453
2 | 12
3 | 4567
3 | 9
I'd like to have a SELECT statement that fetch the first line with chip_id=1,2,3
Like this :
chip_id | sample_id
-------------------
1 | 45 or 55 or whatever
2 | 12 or 453 ...
3 | 9 or ...
How can I do this?
Thanks
i'd probably:
set a variable =0
order your table by chip_id
read the table in row by row
if table[row]>variable, store the table[row] in a result array,increment variable
loop till done
return your result array
though depending on your DB,query and versions you'll probably get unpredictable/unreliable returns.
You can get one value using row_number():
select chip_id, sample_id
from (select chip_id, sample_id,
row_number() over (partition by chip_id order by rand()) as seqnum
) t
where seqnum = 1
This returns a random value. In SQL, tables are inherently unordered, so there is no concept of "first". You need an auto incrementing id or creation date or some way of defining "first" to get the "first".
If you have such a column, then replace rand() with the column.
Provided I understood your output, if you are using PostGreSQL 9, you can use this:
SELECT chip_id ,
string_agg(sample_id, ' or ')
FROM your_table
GROUP BY chip_id
You need to group your data with a GROUP BY query.
When you group, generally you want the max, the min, or some other values to represent your group. You can do sums, count, all kind of group operations.
For your example, you don't seem to want a specific group operation, so the query could be as simple as this one :
SELECT chip_id, MAX(sample_id)
FROM table
GROUP BY chip_id
This way you are retrieving the maximum sample_id for each of the chip_id.
Related
I'd like to create a query that returns a column with a repeating number sequence in it.
For example:
row_num | repeat
----------------
1 | 1
2 | 2
3 | 3
4 | 1
5 | 2
6 | 3
I'm struggling to understand how I could achieve this with BigQuery Standard SQL.
So far i've generated the row number (ROW_NUMBER() OVER()) as row_num in my select, and then I was thinking I could use a modulus function to determine the repeat number, but this would split it into several separate columns, so I'd need additional steps to merge them into the one column. I wondered if there was a more elegant way of achieving this.
Many Thanks!
In fact, the modulus should work here. Assuming your table already has a row_num column, and you want to generate the repeat column, you may try:
SELECT
row_num,
MOD(row_num - 1, 3) + 1 AS repeat
FROM yourTable
ORDER BY
row_num;
I am trying to sort the numbers,
MH/122020/101
MH/122020/2
MH/122020/145
MH/122020/12
How can I sort these in an Access query?
I tried format(mid(first(P.PFAccNo),11),"0") but it didn't work.
You need to use expressions in your ORDER BY clause. For test data
ID PFAccNo
-- -------------
1 MH/122020/101
2 MH/122020/2
3 MH/122020/145
4 MH/122020/12
5 MH/122021/1
the query
SELECT PFAccNo, ID
FROM P
ORDER BY
Left(PFAccNo,9),
Val(Mid(PFAccNo,11))
returns
PFAccNo ID
------------- --
MH/122020/2 2
MH/122020/12 4
MH/122020/101 1
MH/122020/145 3
MH/122021/1 5
you have to convert your substring beginning with pos 11 to a number, and the number can be sorted.
How about this ?
SELECT
tmpTbl.yourFieldName
FROM
tmpTbl
ORDER BY
CLng(Mid([tmpTbl].[yourFieldname],InStrRev([tmpTbl].[yourFieldname],"/")+1));
Given the following data in my test_table, column DATETIMESTAMP:
XXX123
YYY000
XXX-1234
my Statement:
SELECT CInt(Mid(datetimestamp,4)) AS Ausdr1
FROM test_data
ORDER BY 1;
sorts my data. please hange 4 to 11 and it will work for you
I try to call to my DB and where is only one table:
id | value
----------
1 | 1|2|4
2 | 11|23
3 | 1|4|3|11
4 | 2|4|11
5 | 5|6|11
6 | 12|15|16
7 | 3|1|4
8 | 5|2|1
QUERY was : SELECT * FROM table_name WHERE value LIKE '%1%'
I want to select only rows with value 1 but I get rows with 11 value to.
How to show in SQL differences?
If you have to stick with this broken design, it's probably better to use Postgres' ability to parse a string into an array.
This is more robust than using a like condition:
select *
from the_table
where string_to_array(value,'|') #> array['1']
or maybe a bit easier to read
select *
from the_table
where '1' = any (string_to_array(value,'|'))
using the overlaps operator #> you can also search for more than one value at a time:
select *
from the_table
where string_to_array(value,'|') #> array['1','2']
will return all rows where value contains 1 and 2
SQLFiddle example: http://sqlfiddle.com/#!15/8793d/2
I strongly recommend that you should normalize your schema to every column store only atomic values.
Without it, you are forced to do some nasty trick, f.ex. with arrays:
select * from t
where '1' = any (string_to_array(value, '|'))
or, with pattern matching:
select * from t
where '1' similar to value
SQLFiddle
How I can get min difference between two integer fields(value_0 - value)?
value_0 >= value always
value_0 | value
-------------------
15 | 10
12 | 10
15 | 11
11 | 11
Try this:
SELECT MIN(value_0-value) as MinDiff
FROM TableName
WHERE value_0>=value
With the sample data you have given,
Output is 0. (11-11)
See demo in SQL Fiddle.
Read more about MIN() here.
Here is one way:
select min(value_0 - value)
from table t;
This is pretty basic SQL. If you want to see other values on the same row as the minimum, use order by and choose one row:
select (value_0 - value)
from table t
order by (value_0 - value)
limit 1;
The limit 1 works in some databases for getting one row. Others use top 1 in the select clause. Or fetch first 1 rows only. Or even something else.
The issue with 8.3 is that rank() is introduced in 8.4.
Consider the numbers [10,6,6,2].
I wish to achieve a rank of those numbers where the rank is equal to the row number:
rank | score
-----+------
1 | 10
2 | 6
3 | 6
4 | 2
A partial solution is to self-join and count items with a higher or equal, score. This produces:
1 | 10
3 | 6
3 | 6
4 | 2
But that's not what I want.
Is there a way to rank, or even just order by score somehow and then extract that row number?
If you want a row number equivalent to the window function row_number(), you can improvise in version 8.3 (or any version) with a (temporary) SEQUENCE:
CREATE TEMP SEQUENCE foo;
SELECT nextval('foo') AS rn, *
FROM (SELECT score FROM tbl ORDER BY score DESC) s;
db<>fiddle here
Old sqlfiddle
The subquery is necessary to order rows before calling nextval().
Note that the sequence (like any temporary object) ...
is only visible in the same session it was created.
hides any other table object of the same name.
is dropped automatically at the end of the session.
To use the sequence in the same session repeatedly run before each query:
SELECT setval('foo', 1, FALSE);
There's a method using an array that works with PG 8.3. It's probably not very efficient, performance-wise, but will do OK if there aren't a lot of values.
The idea is to sort the values in a temporary array, then extract the bounds of the array, then join that with generate_series to extract the values one by one, the index into the array being the row number.
Sample query assuming the table is scores(value int):
SELECT i AS row_number,arr[i] AS score
FROM (SELECT arr,generate_series(1,nb) AS i
FROM (SELECT arr,array_upper(arr,1) AS nb
FROM (SELECT array(SELECT value FROM scores ORDER BY value DESC) AS arr
) AS s2
) AS s1
) AS s0
Do you have a PK for this table?
Just self join and count items with: a higher or equal score and higher PK.
PK comparison will break ties and give you desired result.
And after you upgrade to 9.1 - use row_number().