Redshift's new super data type uses partiql for querying. I have an array of data that is not nested eg: [0,1,2,3,4]
What is the best way to query this data? All the documentation talks about nested arrays, but this is at the root level and there is no testing.
I have tried select supercolumnname[n] from tablewithsuper; and I am getting nulls, which isn't right.
The best way (that I know right now) is to unnest the array:
CREATE TEMPORARY TABLE my_table (my_array SUPER);
INSERT INTO my_table VALUES (JSON_PARSE('[10001,10002,3333]'));
SELECT m FROM my_table as t, t.my_array as m;
Related
Relatively new SQL user question....
If my postgresql query looks like this:
select
to_timestamp((unnest(enrolled_ranges) ->> 'start_time')::float) as start_time
, to_timestamp((unnest(enrolled_ranges) ->> 'end_time')::float) as end_time
from student_inclusions
where student_id = '123456'
And the initial enrolled_ranges json data is this:
{"{\"start_time\":1536652800.00007,\"end_time\":1563981839.966626}","{\"start_time\":1563982078.624668,\"end_time\":1563989693.830777}"}
Why does sql do this
instead of this
The first answer is what I want, I just don't understand how sql knows from the query to associate the matching start and end times. Do you have any insight?
The documentation on set-returning functions describes the behavior you observed:
For each row from the underlying query, there is an output row using the first result from each set-returning function, then an output row using the second result, and so on.
See also What is the expected behaviour for multiple set-returning functions in SELECT clause?
I am fairly new to DB2 (and SQL in general) and I am having trouble finding an efficient method to DECODE columns
Currently, the database has a number of tables most of which have a significant number of their columns as numbers, these numbers correspond to a table with the real values. We are talking 9,500 different values (e.g '502=yes' or '1413= Graduate Student')
In any situation, I would just do WHERE clause and show where they are equal, but since there are 20-30 columns that need to be decoded per table, I can't really do this (that I know of).
Is there a way to effectively just display the corresponding value from the other table?
Example:
SELECT TEST_ID, DECODE(TEST_STATUS, 5111, 'Approved, 5112, 'In Progress') TEST_STATUS
FROM TEST_TABLE
The above works fine.......but I manually look up the numbers and review them to build the statements. As I mentioned, some tables have 20-30 columns that would need this AND some need DECODE statements that would be 12-15 conditions.
Is there anything that would allow me to do something simpler like:
SELECT TEST_ID, DECODE(TEST_STATUS = *TableWithCodeValues*) TEST_STATUS
FROM TEST_TABLE
EDIT: Also, to be more clear, I know I can do a ton of INNER JOINS, but I wasn't sure if there was a more efficient way than that.
From a logical point of view, I would consider splitting the lookup table into several domain/dimension tables. Not sure if that is possible to do for you, so I'll leave that part.
As mentioned in my comment I would stay away from using DECODE as described in your post. I would start by doing it as usual joins:
SELECT a.TEST_STATUS
, b.TEST_STATUS_DESCRIPTION
, a.ANOTHER_STATUS
, c.ANOTHER_STATUS_DESCRIPTION
, ...
FROM TEST_TABLE as a
JOIN TEST_STATUS_TABLE as b
ON a.TEST_STATUS = b.TEST_STATUS
JOIN ANOTHER_STATUS_TABLE as c
ON a.ANOTHER_STATUS = c.ANOTHER_STATUS
JOIN ...
If things are too slow there are a couple of things you can try:
Create a statistical view that can help determine cardinalities from the joins (may help the optimizer creating a better plan):
https://www.ibm.com/support/knowledgecenter/sl/SSEPGG_9.7.0/com.ibm.db2.luw.admin.perf.doc/doc/c0021713.html
If your license admits you can experiment with Materialized Query Tables (MQT). Note that there is a penalty for modifications of the base tables, so if you have more of a OLTP workload, this is probably not a good idea:
https://www.ibm.com/developerworks/data/library/techarticle/dm-0509melnyk/index.html
A third option if your lookup table is fairly static is to cache the lookup table in the application. Read the TEST_TABLE from the database, and lookup descriptions in the application. Further improvements may be to add triggers that invalidate the cache when lookup table is modified.
If you don't want to do all these joins you could create yourself an own LOOKUP function.
create or replace function lookup(IN_ID INTEGER)
returns varchar(32)
deterministic reads sql data
begin atomic
declare OUT_TEXT varchar(32);--
set OUT_TEXT=(select text from test.lookup where id=IN_ID);--
return OUT_TEXT;--
end;
With a table TEST.LOOKUP like
create table test.lookup(id integer, text varchar(32))
containing some id/text pairs this will return the text value corrseponding to an id .. if not found NULL.
With your mentioned 10k id/text pairs and an index on the ID field this shouldn't be a performance issue as such data amount should be easily be cached in the corresponding bufferpool.
Note: I am using the latest version of Postgres (9.4)
I am trying to write a query which does a simple join of 2 tables, and groups by the primary key of the first table, and does an array_agg of several fields in the 2nd table which I want returned as an object. The array needs to be sorted by a combination of 2 fields in the json objects, and also uniquified.
So far, I have come up with the following:
SELECT
zoo.id,
ARRAY_AGG(
DISTINCT ROW_TO_JSON((
SELECT x
FROM (
SELECT animals.type, animals.name
) x
))::JSONB
-- ORDER BY animals.type, animals.name
)
FROM zoo
JOIN animals ON animals.zooId = zoo.id
GROUP BY zoo.id;
This results in one row for each zoo, with a an aggregate array of jsonb objects, one for each animal, uniquely.
However, I can't seem to figure out how to also sort this by the parameters in the commented out part of the code.
If I take out the distinct, I can ORDER BY original fields, which works great, but then I have duplicates.
If you use row_to_json() you will lose the column names unless you put in a row that is typed. If you "manually" build the jsonb object with json_build_object() using explicit names then you get them back:
SELECT zoo.id, array_agg(za.jb) AS animals
FROM zoo
JOIN (
SELECT DISTINCT ON (zooId, "type", "name")
zooId, json_build_object('animal_type', "type", 'animal_name', "name")::jsonb AS jb
FROM animals
ORDER BY zooId, jb->>'animal_type', jb->>'animal_name'
-- ORDER BY zooId, "type", "name" is far more efficient
) AS za ON za.zooId = zoo.id
GROUP BY zoo.id;
You can ORDER BY the elements of a jsonb object, as shown above, but (as far as I know) you cannot use DISTINCT on a jsonb object. In your case this would be rather inefficient anyway (first building all the jsonb objects, then throwing out duplicates) and at the aggregate level it is plain impossible with standard SQL. You can achieve the same result, however, by applying the DISTINCT clause before building the jsonb object.
Also, avoid use of SQL key words like "type" and standard data types like "name" as column names. Both are non-reserved keywords so you can use them in their proper contexts, but practically speaking your commands could get really confusing. You could, for instance, have a schema, with a table, a column in that table, and a data type each called "type" and then you could get this:
SELECT type::type FROM type.type WHERE type = something;
While PostgreSQL will graciously accept this, it is plain confusing at best and prone to error in all sorts of more complex situations. You can get a long way by double-quoting any key words, but they are best just avoided as identifiers.
I need to create an index from a query that uses json_array_elements()
SELECT *, json_array_elements(nested_json_as_text::json) as elements FROM my_table
Since the json contains multiple elements, the result is that the original index is now duplicated across rows and no longer unique.
I am not very familiar with creating indices and want to avoid doing anything destructive. What is the best way to create a column of unique integers for this case?
Found an answer:
SELECT *, json_array_elements(nested_json_as_text::json) as elements, row_number() over () as my_index FROM my_table
I'm trying to get the whole result of a query into a variable, so I can loop through it and make inserts.
I don't know if it's possible.
I'm new to postgre and procedures, any help will be very welcome.
Something like:
declare result (I don't know what kind of data type I should use to get a query);
select into result label, number, desc from data
Thanks in advance!
I think you have to read PostgreSQL documentation about cursors.
But if you want just insert data from one table to another, you can do:
insert into data2 (label, number, desc)
select label, number, desc
from data
if you want to "save" data from query, you also can use temporary table, which you can create by usual create table or create table as:
create temporary table temp_data as
(
select label, number, desc
from data
)
see documentation