I´m just starting with views in Postgresql 9.1 and have following question.
Given are the following tables:
pupils
name | age
============
john 15
jack 16
cars
type | owner
============
volvo 1
vw 2
Is it possible to create a view that gives me this as result
ident | column
==============
john pupils
jack pupils
volvo cars
vw cars
My example might look a bit abstract but I´m in the the need to create one view from very different tables which all share one column which I´m interested in but except this have nothing in common.
My poor first step:
CREATE OR REPLACE VIEW test AS
SELECT pupils.name, cars.type AS ident
FROM pupils,cats
thanks,
t book
You don't want a cartesian join between the two tables, you want a UNION
create or replace view test
as
select name as ident,
'pupils' as table_source
from pupils
union all
select type,
'cars'
FROM cars
union all
select cloud_number,
'clouds'
FROM clouds
select tree_name,
'trees'
FROM trees;
You can add any number of tables to this. The only restriction is that the common column must have a "compatible" data type (e.g. all varchar). If e.g. the 5th table has a date column that you want to include you need to add an explicit type case (or use a formatting function).
The column names of the result are determined by the column names of the first select in the union.
Alternatively you could also name them in the create view part
create or replace view (ident, some_column) test
as
select ...
Related
I have 2 tables with the exact same number of rows and the same non-repeated id. Because the data comes from 2 sources I want to keep it 2 tables and not combine it. I assume the best approach would be to leave the unique id as the primary key and join on it?
SELECT * FROM tableA INNER JOIN tableB ON tableA primary key = tableB primary key
The data is used by an application that force the user to select 1 or many values from 5 drop downs in cascading order:
select 1 or many values from tableA column1.
select 1 or many values from tableA column2 but filtered from the first filter.
select 1 or many values from tableA column3 but filtered from the second filter which in turn is filtered from the first filter.
For example:
pk
Column 1
Column 2
Column 3
123
Doe
Jane
2022-01
234
Doe
Jane
2021-12
345
Doe
John
2022-03
456
Jones
Mary
2022-04
Selecting "Doe" from column1 would limit the second filter to ("Jane","John"). And selecting "Jane" from column2 would filter column3 to ("2022-01","2021-12")
And last part of the question;
The application have 3 selection options for column3:
picking the exact value (for example "2022-01") or picking the year ("2022") or picking the quarter that the month falls into ("Q1", which equates in "01","02","03").
What would be the best usage of indexes AND/OR additional columns for this scenario?
Volume of data would be 20-100 million rows.
Each filter is in the range of 5-25 distinct values.
Which version of Postgres do you operate?
The volume you state is rather daunting for such a use case of populating drop-down boxes using live data for a PG db.
No kidding, it's possible, Kibana/Elastic has even a filter widget that works exactly this way for instance.
My guess is you may consider storing the different combinations of search columns in another table simply to speed up populating the dropboxes. You can achieve that with triggers on the two main tables. So instead of additional columns/indexes you may end with an additional table ;)
Regarding indexing strategy and given the hints you stated (AND/OR), I'd say there's no silver bullet. Index the columns that will be queried the most often.
Index each column individually because Postgres starting from 11 IIRC can combine multiple indexes to answer conjunctive/disjunctive formulas in WHERE clauses.
Hope this helps
I am looking for some help with trying to link 2 sheets that have a number of Filters that I have setup but are both sitting in separate tables. The reason this is because I have a number of aggregated columns that are different for the 2 tables and want to keep this separately as I will be building more sheets as I go along.
The filters that are the same within the 2 sheets are the following:
we_date
product
manager
patch
Through the data manager I managed to create an association between the 2 tables for we_date but from reading on this site and other searches on Google I can't make any associations between these tables and this is where I am stuck.
The 2 sheets will now allow me to filter using the we_date, but if I use the filters for product, manager or patch then nothing happens on my 2nd sheet as they are not linked.
Currently in my data load editor I have 2 sections of select queries like the following:
Table1
QUALIFY *;
w:
SELECT
*
FROM
table1
;
UNQUALIFY *;
Table2
QUALIFY *;
w_c:
SELECT
*
FROM
table2
;
UNQUALIFY *;
I would really appreciate if somebody could advise a fix on the issue I am having.
In Qlik, field names of identical values from different tables are automatically associated.
When you're calling Qualify *, you're actually renaming all field names and explicitly saying NOT to associate.
Take a look at the Qlik Sense documentation on Qualify *:
The automatic join between fields with the same name in different
tables can be suspended by means of the qualify statement, which
qualifies the field name with its table name. If qualified, the field
name(s) will be renamed when found in a table. The new name will be in
the form of tablename.fieldname. Tablename is equivalent to the label
of the current table, or, if no label exists, to the name appearing
after from in LOAD and SELECT statements.
We can use as to manually reassign field names.
SELECT customer_id, private_info as "private_info_1", favorite_dog from table1;
SELECT customer_id, private_info as "private_info_2", car from table2;
Or, we can correctly use Qualify. Example:
table1 and table2 have a customer_id field, and private_info field. We want customer_id field to be the associative value, and private_info to not be. We would use QUALIFY on private_info, which Qlik would then rename based on file name.
QUALIFY private_info;
SELECT * from table1;
SELECT * from table2;
The following field names would then be: customer_id (associated), and table1.private_info, and table2.private_info
I have a table contains columns 'employeename' and 'id', how can I sort the 'employeename' column following alphabetical order of the names initial?
Say the table is like this now:
employeename rid eid
Dave 1 1
Ben 4 2
Chloe 6 6
I tried the command ORDER BY, it shows what I want but when I query the data again by SELECT, the showed table data is the same as original, indicting ORDER BY does not modify the data, is this correct?
SELECT *
FROM employee
ORDER BY employeename ASC;
I expect the table data to be modified (sorted by names alphabetical order) like this:
employeename rid eid
Ben 4 2
Chloe 6 6
Dave 1 1
the showed table data is the same as original, indicting ORDER BY does not modify the data, is this correct?
Yes, this is correct. A SELECT statement does not change the data in a table. Only UPDATE, DELETE, INSERT or TRUNCATE statements will change the data.
However, your question shows a misconception on how a relational database works.
Rows in a table (of a relational database) are not sorted in any way. You can picture them as balls in a basket.
If you want to display data in a specific sort order, the only (really: the only) way to do that is to use an ORDER BY in your SELECT statement. There is no alternative to that.
Postgres allows to define a VIEW that includes an ORDER BY which might be an acceptable workaround for you:
CREATE VIEW sorted_employee;
AS
SELECT *
FROM employee
ORDER BY employeename ASC;
Then you can simply use
select *
from sorted_employees;
But be aware of the drawbacks. If you run select * from sorted_employees order by id then the data will be sorted twice. Postgres is not smart enough to remove the (useless) order by from the view's definition.
Some related questions:
Default row order in SELECT query - SQL Server 2008 vs SQL 2012
What is the default SQL result sort order with 'select *'?
Is PostgreSQL order fully guaranteed if sorting on a non-unique attribute?
Why do results from a SQL query not come back in the order I expect?
I'm dealing with a lot of unique data that has the same type of columns, but each group of rows have different attributes about them and I'm trying to see if PostgreSQL has a way of storing metadata about groups of rows in a database or if I would be better off adding custom columns to my current list of columns to track these different attributes. Microsoft Excel for instance has a way you can merge multiple columns into a super-column to group multiple columns into one, but I don't know how this would translate over to a PostgreSQL database. Thoughts anyone?
Right, can't upload files. Hope this turns out well.
Section 1 | Section 2 | Section 3
=================================
Num1|Num2 | Num1|Num2 | Num1|Num2
=================================
132 | 163 | 334 | 1345| 343 | 433
......
......
......
have a "super group" of columns (In SQL in general, not just postgreSQL), the easiest approach is to use multiple tables.
Example:
Person table can have columns of
person_ID, first_name, last_name
employee table can have columns of
person_id, department, manager_person_id, salary
customer table can have columns of
person_id, addr, city, state, zip
That way, you can join them together to do whatever you like..
Example:
select *
from person p
left outer join student s on s.person_id=p.person_id
left outer join employee e on e.person_id=p.person_id
Or any variation, while separating the data into different types and PERHAPS save a little disk space in the process (example if most "people" are "customers", they don't need a bunch of employee data floating around or have nullable columns)
That's how I normally handle this type of situation, but without a practical example, it's hard to say what's best in your scenario.
I have a table which stores 'links' between 2 people. In order prevent further complications down the road on an application I am building, I want to create an editable view, that shows the link records and an inverse copy of the link records.
Meaning if Joe is linked to Sally, then the view should show Joe linked to Sally and Sally linked to Joe.
So I have created a UNION as follows:
CREATE VIEW links AS
SELECT id,
link_origin_id AS person_id,
link_origin_id,
link_rcvd_id,
link_type,
link_summary,
created_at,
updated_at
FROM links_data
UNION
SELECT id,
link_rcvd_id,
link_origin_id,
link_rcvd_id,
link_type,
link_summary,
created_at,
updated_at
FROM links_data
The view works fine. Note that the view creates an additional column 'person_id' which is not in the underlying table.
I am running into trouble creating postgres rules that will edit the underlying table.
Specifically, I can successfully edit a table view when it is not a UNION view. But below is what occurs when I try to write a rule with a UNION view:
CREATE RULE inverse_links AS ON INSERT TO links DO INSTEAD
INSERT INTO links_data
(id, link_origin_id, link_type, link_summary, link_rcvd_id, created_at,
updated_at)
VALUES (nextval('people_id_seq'), new.link_origin_id, new.link_type,
new.link_summary, new.link_rcvd_id, new.created_at, new.updated_at)
RETURNING *;
The above rule should redirect the edits to the underlying table 'links_data'.
But I am getting the following error:
ERROR: RETURNING list's entry 3 has different type from column "link_origin_id"
********** Error **********
ERROR: RETURNING list's entry 3 has different type from column "link_origin_id"
SQL state: 42P17
The 2 things I feel might be the problem is that 1) the view has an additional column which is causing the column types to not match up or 2) there might be something with the fact that the table is a UNION on itself and editing this might be a problem.
Any idea of where I can go with this?
Disclaimer: almost no experience with updatable views.
Your RETURNING clause is the problem - the links_data table most probably has 7 colums (as shown by your view definition and the ON INSERT rule) and you're returning their contents for the just inserted row with RETURNING * but your view has 8 columns. Check and sync those two lists.