I have the following tables:
business
id catid subcatid
---------------------
10 {1} {10,20}
20 {2} {30,40}
30 {3} {50,60,70}
cat_subcat
catid shortname parent_id bid
--------------------------------------------
1 A 10
2 B 20
3 c 30
10 x 1 10
20 y 1 10
30 z 2 20
40 w 2 20
Both the tables have a relationship using id. The problem I am getting is outlined below. Here is my query currently:
SELECT ARRAY[category_id]::int[] from cat_subcat
where parentcategoryid IS not NULL and shortname ilike ('x,y');
I want to get the category_id for an entered shortname, but my query is not giving the proper output. If I pass one shortname it will retrieve the category_id, but if I pass more than one shortname it will not display category_id. Please tell me how to get the category_id for more than one shortname passed.
To actually use pattern matching with ILIKE, you cannot use a simple IN expression. Instead, you need ILIKE ANY (...) or ALL (...), depending on whether you want the tests ORed or ANDed:
Also, your ARRAY constructor will be applied to individual rows, which seems rather pointless. I assume you want this instead (educated guess):
SELECT array_agg(catid) AS cats
FROM cat_subcat
WHERE parent_id IS NOT NULL
AND shortname ILIKE ANY ('{x,y}');
Well, as long as you don't use wildcards (%, _) for your pattern, you can translate this to:
AND lower(shortname) IN ('x','y');
But that would be rather pointless, since Postgres internally converts this to:
AND lower(shortname) = ANY ('{x,y}');
.. before evaluating.
Related
I'd like to obtain is the first ocurrence of non-null value per category.
If there are just null values, the result of this category shall be NULL.
For a table like this:
Category Value
1 NULL
1 1922
2 23
2 99
3 NULL
3 NULL
the result should be
Category Value
1 1922
2 23
3 NULL
How can this be achieved using postgres?
Unfortunately the two features that would make this trivial are not implemented in postgresql
IGNORE NULLS in FIRST_VALUE, LAST_VALUE
FILTER clause in non-aggregate window functions
However, you can hack the desired result using groupby & array_agg , which does support the FILTER clause, and then pick the first element using square-bracket syntax. (recall that postgresql array indexing starts with 1)
Also, I would advise that you provide an explicit ordering for the aggregation step. Otherwise the value that ends up as the first element would depend on the query plan & physical data layout of the underlying table.
WITH vals (category, val) AS ( VALUES
(1,NULL),
(1,1922),
(2,23),
(2,99),
(3,NULL),
(3,NULL)
)
SELECT
category
, (ARRAY_AGG(val) FILTER (WHERE val IS NOT NULL))[1]
FROM vals
GROUP BY 1
produces the following output:
category | array_agg
----------+-----------
1 | 1922
3 |
2 | 23
(3 rows)
I am comparing from different table to get the COLUMN_NAME of the MAXIMUM value
Examples.
These are example tables: Fruit_tb, Vegetable_tb, State_tb, Foods_tb
Under Fruit_tb
fr_id fruit_one fruit_two
1 20 50
Under Vegetables_tb (v = Vegetables)
v_id v_one V_two
1 10 9
Under State_tb
stateid stateOne stateTwo
1 70 87
Under Food_tb
foodid foodOne foodTwo
1 10 3
Now here is the scenario, I want to get the COLUMN NAMES of the max or greatest value in each table.
You can maybe find out the row which contains the max value of a column. For eg:
SELECT fr_id , MAX(fruit_one) FROM Fruit_tb GROUP BY fr_id;
In order to find the out the max value of a table:
SELECT fr_id ,fruit_one FROM Fruit_tb WHERE fruit_one<(SELECT max(fruit_one ) from Fruit_tb) ORDER BY fr_id DESC limit 1;
A follow up SO for the above scenario.
Maybe you can use GREATEST in order to get the column name which has the max value. But then what I'm not sure is whether you'll be able to retrieve all the columns of different tables at once. You can do something like this to retrieve from a single table:
SELECT CASE GREATEST(`id`,`fr_id`)
WHEN `id` THEN `id`
WHEN `fr_id` THEN `fr_id`
ELSE 0
END AS maxcol,
GREATEST(`id`,`fr_id`) as maxvalue FROM Fruit_tb;
Maybe this SO could help you. Hope it helps!
How can I write a calculation field in a table that outputs '1' if there are other (related) records in the same table that meet a given set of criteria and '0' otherwise?
Here's my problem explained in more detail:
I have a table containing 'students' and another containing 'exam results'. The 'exam results' table looks like this:
StudentID SubjectID Level Result
3234 1 2 A-
3234 2 4 B+
4739 1 4 C+
A student can only pass a Level 4 exam in subject 2 if they have also passed a Level 2 exam in subject 1 with a B+ or higher. I want to define a field in the 'students' table that contains a '1' if there exists an exam result belonging to the right student that meets these criteria and a '0' otherwise.
What would be the best way to do this?
Let us take an example of a Results table where the results are also calculated as a numeric value, e.g.
StudentID SubjectID Level Result cResultNum
3234 1 2 A- 95
3234 2 4 B+ 85
4739 1 4 C+ 75
and an Exams table with the following fields (among others):
RequiredSubjectID
RequiredLevel
RequiredResultNum
Given these, you can construct a relationship between Exams and (another occurrence of) Results as:
Exams::RequiredSubjectID = Results 2::SubjectID
AND
Exams::RequiredLevel = Results 2::Level
AND
Exams::RequiredResultNum ≤ Results 2::cResultNum
This allows each exam record to calculate a list of students that are eligible to take that exam as =
List ( Results 2::StudentID )
I want to define a field in the 'students' table that contains a '1'
if there exists an exam result belonging to the right student that
meets these criteria and a '0' otherwise.
This request is unclear, because there are many exams a student may want to take, and a field in the Students table can calculate only one result.
You need to do a self-join in the table for the field you want to check, for example:
Exam::Level = Exam2::Level
Exam::Student = Exam2::Student
And for the "was passed" criteria I think you could do an "If" on the calculation like this:
If ( Last(Exam2::Result) = "D" and ...(all the pass values) ; 1 ; 0 )
Edit:
It could be just with the not pass value hehe I miss that it will be like this:
If ( Last(Exam2::Result) = "F" ; 0 ; 1 )
I hope this helps you.
I'm trying to find a way to use Perl to further process a PostgreSQL output. If there's a better way to do this via PostgreSQL, please let me know. I basically need to choose certain columns (Realtime, Value) in a file to concatenate certains columns to create a row while keeping ID and CAT.
First time posting, so please let me know if I missed anything.
Input:
ID CAT Realtime Value
A 1 time1 55
A 1 time2 57
B 1 time3 75
C 2 time4 60
C 3 time5 66
C 3 time6 67
Output:
ID CAT Time Values
A 1 time 1,time2 55,57
B 1 time3 75
C 2 time4 60
C 3 time5,time6 66,67
You could do this most simply in Postgres like so (using array columns)
CREATE TEMP TABLE output AS SELECT
id, cat, ARRAY_AGG(realtime) as time, ARRAY_AGG(value) as values
FROM input GROUP BY id, cat;
Then select whatever you want out of the output table.
SELECT id
, cat
, string_agg(realtime, ',') AS realtimes
, string_agg(value, ',') AS values
FROM input
GROUP BY 1, 2
ORDER BY 1, 2;
string_agg() requires PostgreSQL 9.0 or later and concatenates all values to a delimiter-separated string - while array_agg() (v8.4+) creates am array out of the input values.
About 1, 2 - I quote the manual on the SELECT command:
GROUP BY clause
expression can be an input column name, or the name or ordinal number
of an output column (SELECT list item), or ...
ORDER BY clause
Each expression can be the name or ordinal number of an output column
(SELECT list item), or
Emphasis mine. So that's just notational convenience. Especially handy with complex expressions in the SELECT list.
Running this query:
select name from folders order by name
returns these results:
alphanumeric
a test
test 20
test 19
test 1
test 10
But I expected:
a test
alphanumeric
test 1
test 10
test 19
test 20
What's wrong here?
You can simply cast name column to bytea data type allowing collate-agnostic ordering:
SELECT name
FROM folders
ORDER BY name::bytea;
Result:
name
--------------
a test
alphanumeric
test 1
test 10
test 19
test 20
(6 rows)
All of this methods sorted my selection in alphabetical order:
test 1
test 10
test 2
test 20
This solution worked for me (lc_collate: 'ru_RU.UTF8'):
SELECT name
FROM folders
ORDER BY SUBSTRING(name FROM '([0-9]+)')::BIGINT ASC, name;
test 1
test 2
test 10
test 20
select * from "public"."directory" where "directoryId" = 17888 order by
COALESCE(SUBSTRING("name" FROM '^(\d+)')::INTEGER, 99999999),
SUBSTRING("name" FROM '[a-zA-z_-]+'),
COALESCE(SUBSTRING("name" FROM '(\d+)$')::INTEGER, 0),
"name";
NOTE: Escape the regex as you need, in some languages, you will have to add one more "\".
In my Postgres DB, name column contains following, when I use simple order by name query:
1
10
2
21
A
A1
A11
A5
B
B2
B22
B3
M 1
M 11
M 2
Result of Query, After I have modified it:
1
2
10
21
A
A1
A5
A11
B
B2
B3
B22
M 1
M 2
M 11
You may be able to manually sort by splitting the text up in case there is trailing numerals, like so:
SELECT * FROM sort_test
ORDER BY SUBSTRING(text FROM '^(.*?)( \\d+)?$'),
COALESCE(SUBSTRING(text FROM ' (\\d+)$')::INTEGER, 0);
This will sort on column text, first by all characters optionally excluding an ending space followed by digits, then by those optional digits.
Worked well in my test.
Update fixed the string-only sorting with a simple coalesce (duh).
OverZealous answer helped me but didn't work if the string in the database begun with numbers followed by additional characters.
The following worked for me:
SELECT name
FROM folders
ORDER BY
COALESCE(SUBSTRING(name FROM '^(\\d+)')::INTEGER, 99999999),
SUBSTRING(name FROM '^\\d* *(.*?)( \\d+)?$'),
COALESCE(SUBSTRING(name FROM ' (\\d+)$')::INTEGER, 0),
name;
So this one:
Extracts the first number in the string, or uses 99999999.
Extracts the string that follows the possible first number.
Extracts a trailing number, or uses 0.
A Vlk's answer above helped me a lot, but it sorted items only by the numeric part, which in my case came second. My data was like (desk 1, desk 2, desk 3 ...) a string part, a space and a numeric part. The syntax in A Vlk's answer returned the data sorted by the number, and at that it was the only answer from the above that did the trick. However when the string part was different, (eg desk 3, desk 4, table 1, desk 5...) table 1 would get first from desk 2. I fixed this using the syntax below:
...order by SUBSTRING(name,'\\w+'), SUBSTRINGname FROM '([0-9]+)')::BIGINT ASC;
Tor's last SQL worked for me. However if you are calling this code from php you need add extra slashes.
SELECT name
FROM folders
ORDER BY
COALESCE(SUBSTRING(name FROM '^(\\\\d+)')::INTEGER, 99999999),
SUBSTRING(name FROM '^\\\\d* *(.*?)( \\\\d+)?$'),
COALESCE(SUBSTRING(name FROM ' (\\\\d+)$')::INTEGER, 0),
name;