How to apply a function with arguments on every element in a text array in Postgresql SQL queries
Lets say My text array is
["abc-123-x", "def-123-y", "hij-234-k", "klm-232-p", "nop-3434-9", "qrs-23-p9"]
the result should be
[x,y,k,p,9,p9]
you need to unnest the array, extract the characters, then aggregate back:
select array_agg(right(t.w, 1))
from unnest(array['abc','def','hij','klm','nop','qrs']) as t(w);
Related
This is not working correctly:
SELECT array_remove(array_agg(s1->>'karten'),'8 eich.jpg') from spiele;
The output: ["3 eich.jpg","8 eich.jpg","5 sche.jpg","2 herz.jpg","1 laub.jpg","4 eich.jpg","2 sche.jpg","5 laub.jpg","4 herz.jpg","4 sche.jpg"]
The datatype of s1 is json; s1->>'karten' is an array
If karten refers to a JSON array in the, then s1 ->> 'karten doesn't return each element individually, but a one string representing the array. So array_agg() doesn't really aggregate multiple values - only one. The result is an array with a single element - that happens to look like a JSON array.
You can remove an element from a JSON array if the values is jsonb (the recommended data type to handle JSON in Postgres anyway) using the - operator:
select (s1 -> 'karten')::jsonb - '8 eich.jpg'
will return a jsonb value that is an without the key '8 eich.jpg'.
Unfortunately there is no easy conversion from a JSON array to a native array. Search this site, there are multiple answers for that.
I have a table in Athena where one of the columns is of type array.
I tried the below query to get output containing earth but doesn't work.
How do I perform a wildcard search in this column?
Expected output after wildcard search:
select * from mytable
where contains(myarr,'eart%');
This is from memory, so it might need a bit of tweaking, but you can use a filter on the array elements
where cardinality(filter(myarr, q -> q like 'eart%')) > 0
filter creates an array of matches and cardinality tests for one or more elements in the array
I am trying to SELECT and parse a javascript list in a postgres table column, it has no keys:
{coastal,transitional,contemporary,romantic,traditional,
industrial,modern,contemporary_eclectic,regency,mediterranean}
What SQL command get's the nth value?
I know you can get values by key like this:
SELECT {column_name}->>{key value}
FROM {table_name}
But I really want to just pull values by list-value order. Is there some syntax that I cannot find? Or do I need to transform this array into a different data type?
The same actually works for arrays:
{column_name}->>N
where N is the integer position of an element.
References:
https://www.postgresql.org/docs/current/static/functions-json.html
Turns out I asked the wrong question--I have a postgres array, not a JSON:
I was struggling because posgres starts counting arrays at position 1, not 0--doh!
{column_name}[1] //this is the first value in the array
I have some data in a postgres table that is a string representation of an array of json data, like this:
[
{"UsageInfo"=>"P-1008366", "Role"=>"Abstract", "RetailPrice"=>2, "EffectivePrice"=>0},
{"Role"=>"Text", "ProjectCode"=>"", "PublicationCode"=>"", "RetailPrice"=>2},
{"Role"=>"Abstract", "RetailPrice"=>2, "EffectivePrice"=>0, "ParentItemId"=>"396487"}
]
This is is data in one cell from a single column of similar data in my database.
The datatype of this stored in the db is varchar(max).
My goal is to find the average RetailPrice of EVERY json item with "Role"=>"Abstract", including all of the json elements in the array, and all of the rows in the database.
Something like:
SELECT avg(json_extract_path_text(json_item, 'RetailPrice'))
FROM (
SELECT cast(json_items to varchar[]) as json_item
FROM my_table
WHERE json_extract_path_text(json_item, 'Role') like 'Abstract'
)
Now, obviously this particular query wouldn't work for a few reasons. Postgres doesn't let you directly convert a varchar to a varchar[]. Even after I had an array, this query would do nothing to iterate through the array. There are probably other issues with it too, but I hope it helps to clarify what it is I want to get.
Any advice on how to get the average retail price from all of these arrays of json data in the database?
It does not seem like Redshift would support the json data type per se. At least, I found nothing in the online manual.
But I found a few JSON function in the manual, which should be instrumental:
JSON_ARRAY_LENGTH
JSON_EXTRACT_ARRAY_ELEMENT_TEXT
JSON_EXTRACT_PATH_TEXT
Since generate_series() is not supported, we have to substitute for that ...
SELECT tbl_id
, round(avg((json_extract_path_text(elem, 'RetailPrice'))::numeric), 2) AS avg_retail_price
FROM (
SELECT *, json_extract_array_element_text(json_items, pos) AS elem
FROM (VALUES (0),(1),(2),(3),(4),(5)) a(pos)
CROSS JOIN tbl
) sub
WHERE json_extract_path_text(elem, 'Role') = 'Abstract'
GROUP BY 1;
I substituted with a poor man's solution: A dummy table counting from 0 to n (the VALUES expression). Make sure you count up to the maximum number of possible elements in your array. If you need this on a regular basis create an actual numbers table.
Modern Postgres has much better options, like json_array_elements() to unnest a json array. Compare to your sibling question for Postgres:
Can get an average of values in a json array using postgres?
I tested in Postgres with the related operator ->>, where it works:
SQL Fiddle.
I have a column in our database called min_crew that has varying character arrays such as '{CA, FO, FA}'.
I have a query where I'm trying to get aggregates of these arrays without success:
SELECT use.user_sched_id, array_agg(se.sched_entry_id) AS seids
, array_agg(se.min_crew)
FROM base.sched_entry se
LEFT JOIN base.user_sched_entry use ON se.sched_entry_id = use.sched_entry_id
WHERE se.sched_entry_id = ANY(ARRAY[623, 625])
GROUP BY user_sched_id;
Both 623 and 625 have the same use.user_sched_id, so the result should be the grouping of the seids and the min_crew, but I just keep getting this error:
ERROR: could not find array type for data type character varying[]
If I remove the array_agg(se.min_crew) portion of the code, I do get a table returned with the user_sched_id = 2131 and seids = '{623, 625}'.
The standard aggregate function array_agg() only works for base types, not array types as input.
(But Postgres 9.5+ has a new variant of array_agg() that can!)
You could use the custom aggregate function array_agg_mult() as defined in this related answer:
Selecting data into a Postgres array
Create it once per database. Then your query could work like this:
SELECT use.user_sched_id, array_agg(se.sched_entry_id) AS seids
,array_agg_mult(ARRAY[se.min_crew]) AS min_crew_arr
FROM base.sched_entry se
LEFT JOIN base.user_sched_entry use USING (sched_entry_id)
WHERE se.sched_entry_id = ANY(ARRAY[623, 625])
GROUP BY user_sched_id;
There is a detailed rationale in the linked answer.
Extents have to match
In response to your comment, consider this quote from the manual on array types:
Multidimensional arrays must have matching extents for each dimension.
A mismatch causes an error.
There is no way around that, the array type does not allow such a mismatch in Postgres. You could pad your arrays with NULL values so that all dimensions have matching extents.
But I would rather translate the arrays to a comma-separated lists with array_to_string() for the purpose of this query and use string_agg() to aggregate the text - preferably with a different separator. Using a newline in my example:
SELECT use.user_sched_id, array_agg(se.sched_entry_id) AS seids
,string_agg(array_to_string(se.min_crew, ','), E'\n') AS min_crews
FROM ...
Normalize
You might want to consider normalizing your schema to begin with. Typically, you would implement such an n:m relationship with a separate table like outlined in this example:
How to implement a many-to-many relationship in PostgreSQL?