I have a table named conditions on a schema named test. I created a hypertable and inserted hundreds of rows.
When I run select show_chunks(), it works and displays chunks but I cannot use the table name as parameter as suggested in the manual. This does not work:
SELECT show_chunks("test"."conditions");
How can I fix this?
Ps: I want to query the chunk itself by its name? How can I do this?
The show_chunks expects a regclass, which depending on your current search path means you need to schema qualify the table.
The following should work:
SELECT public.show_chunks('test.conditions');
The double quotes are only necessary if your table is a delimited identifier, for example if your tablename contains a space, you would need to add the double quotes for the identifier. You will still need to wrap it in single quotes though:
SELECT public.show_chunks('test."equipment conditions"');
SELECT public.show_chunks('"test schema"."equipment conditions"');
For more information about identifier quoting:
https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
Edit: Addressing the PS:
I want to query the chunk itself by its name? How can I do this?
feike=# SELECT public.show_chunks('test.conditions');
show_chunks
--------------------------------------------
_timescaledb_internal._hyper_28_1176_chunk
_timescaledb_internal._hyper_28_1177_chunk
[...]
SELECT * FROM _timescaledb_internal._hyper_28_1176_chunk;
Does PostgreSQL support computed / calculated columns, like MS SQL Server? I can't find anything in the docs, but as this feature is included in many other DBMSs I thought I might be missing something.
Eg: http://msdn.microsoft.com/en-us/library/ms191250.aspx
Postgres 12 or newer
STORED generated columns are introduced with Postgres 12 - as defined in the SQL standard and implemented by some RDBMS including DB2, MySQL, and Oracle. Or the similar "computed columns" of SQL Server.
Trivial example:
CREATE TABLE tbl (
int1 int
, int2 int
, product bigint GENERATED ALWAYS AS (int1 * int2) STORED
);
fiddle
VIRTUAL generated columns may come with one of the next iterations. (Not in Postgres 15, yet).
Related:
Attribute notation for function call gives error
Postgres 11 or older
Up to Postgres 11 "generated columns" are not supported.
You can emulate VIRTUAL generated columns with a function using attribute notation (tbl.col) that looks and works much like a virtual generated column. That's a bit of a syntax oddity which exists in Postgres for historic reasons and happens to fit the case. This related answer has code examples:
Store common query as column?
The expression (looking like a column) is not included in a SELECT * FROM tbl, though. You always have to list it explicitly.
Can also be supported with a matching expression index - provided the function is IMMUTABLE. Like:
CREATE FUNCTION col(tbl) ... AS ... -- your computed expression here
CREATE INDEX ON tbl(col(tbl));
Alternatives
Alternatively, you can implement similar functionality with a VIEW, optionally coupled with expression indexes. Then SELECT * can include the generated column.
"Persisted" (STORED) computed columns can be implemented with triggers in a functionally equivalent way.
Materialized views are a related concept, implemented since Postgres 9.3.
In earlier versions one can manage MVs manually.
YES you can!! The solution should be easy, safe, and performant...
I'm new to postgresql, but it seems you can create computed columns by using an expression index, paired with a view (the view is optional, but makes makes life a bit easier).
Suppose my computation is md5(some_string_field), then I create the index as:
CREATE INDEX some_string_field_md5_index ON some_table(MD5(some_string_field));
Now, any queries that act on MD5(some_string_field) will use the index rather than computing it from scratch. For example:
SELECT MAX(some_field) FROM some_table GROUP BY MD5(some_string_field);
You can check this with explain.
However at this point you are relying on users of the table knowing exactly how to construct the column. To make life easier, you can create a VIEW onto an augmented version of the original table, adding in the computed value as a new column:
CREATE VIEW some_table_augmented AS
SELECT *, MD5(some_string_field) as some_string_field_md5 from some_table;
Now any queries using some_table_augmented will be able to use some_string_field_md5 without worrying about how it works..they just get good performance. The view doesn't copy any data from the original table, so it is good memory-wise as well as performance-wise. Note however that you can't update/insert into a view, only into the source table, but if you really want, I believe you can redirect inserts and updates to the source table using rules (I could be wrong on that last point as I've never tried it myself).
Edit: it seems if the query involves competing indices, the planner engine may sometimes not use the expression-index at all. The choice seems to be data dependant.
One way to do this is with a trigger!
CREATE TABLE computed(
one SERIAL,
two INT NOT NULL
);
CREATE OR REPLACE FUNCTION computed_two_trg()
RETURNS trigger
LANGUAGE plpgsql
SECURITY DEFINER
AS $BODY$
BEGIN
NEW.two = NEW.one * 2;
RETURN NEW;
END
$BODY$;
CREATE TRIGGER computed_500
BEFORE INSERT OR UPDATE
ON computed
FOR EACH ROW
EXECUTE PROCEDURE computed_two_trg();
The trigger is fired before the row is updated or inserted. It changes the field that we want to compute of NEW record and then it returns that record.
PostgreSQL 12 supports generated columns:
PostgreSQL 12 Beta 1 Released!
Generated Columns
PostgreSQL 12 allows the creation of generated columns that compute their values with an expression using the contents of other columns. This feature provides stored generated columns, which are computed on inserts and updates and are saved on disk. Virtual generated columns, which are computed only when a column is read as part of a query, are not implemented yet.
Generated Columns
A generated column is a special column that is always computed from other columns. Thus, it is for columns what a view is for tables.
CREATE TABLE people (
...,
height_cm numeric,
height_in numeric GENERATED ALWAYS AS (height_cm * 2.54) STORED
);
db<>fiddle demo
Well, not sure if this is what You mean but Posgres normally support "dummy" ETL syntax.
I created one empty column in table and then needed to fill it by calculated records depending on values in row.
UPDATE table01
SET column03 = column01*column02; /*e.g. for multiplication of 2 values*/
It is so dummy I suspect it is not what You are looking for.
Obviously it is not dynamic, you run it once. But no obstacle to get it into trigger.
Example on creating an empty virtual column
,(SELECT *
From (values (''))
A("virtual_col"))
Example on creating two virtual columns with values
SELECT *
From (values (45,'Completed')
, (1,'In Progress')
, (1,'Waiting')
, (1,'Loading')
) A("Count","Status")
order by "Count" desc
I have a code that works and use the term calculated, I'm not on postgresSQL pure tho we run on PADB
here is how it's used
create table some_table as
select category,
txn_type,
indiv_id,
accum_trip_flag,
max(first_true_origin) as true_origin,
max(first_true_dest ) as true_destination,
max(id) as id,
count(id) as tkts_cnt,
(case when calculated tkts_cnt=1 then 1 else 0 end) as one_way
from some_rando_table
group by 1,2,3,4 ;
A lightweight solution with Check constraint:
CREATE TABLE example (
discriminator INTEGER DEFAULT 0 NOT NULL CHECK (discriminator = 0)
);
I am trying to read hstore data from source and insert into target hstore column. But for some weird reason the data has some single quotes in it and I cannot delete or remove them. Source hstore data looks something like
Value 1: "Target_Payment_Type"=>"Auto_Renew", "Target_Membership_term"=>"1 Year"
Value 2: "Target_Payment_Type"=>"'Auto_Renew'", "Target_Membership_term"=>"'1 Year'"
The transformation works fine with the 1st value but fails when at Value2. Can could anyone suggest me a way I can escape the single quotes which may appear in data using pentaho or postgresql (source & target database). Thanks in advance.
At least, you can use postgres replace function in Table Input step:
SELECT
,all_your_non_string_columns
,replace(string_column,'''', '') //note that '''' represents '
FROM
your_table
Real solution you could find in up-to-date driver perhaps.
I installed the war file distribution using the install scripts in buildomatic. The installation is successful but when I boot tomcat server it shows some database exceptions
https://gist.github.com/shruti-palshikar/5ae801674dbd2a537518
I checked if the latest postgres driver exists in the tomcat/lib.
I also checked if the database 'jasperserver' has all the necessary tables
However these tables are empty , does anyone know which script loads data into tables?
Any help is appreciated
The actual error from PostgreSQL is:
relation "jiresourcefolder" does not exist
The query seems to be:
select this_.id as id5_0_, this_.version as version5_0_, this_.uri as uri5_0_, this_.hidden as hidden5_0_, this_.name as name5_0_, this_.label as label5_0_, this_.description as descript7_5_0_, this_.parent_folder as parent8_5_0_, this_.creation_date as creation9_5_0_, this_.update_date as update10_5_0_
from JIResourceFolder this_ where (this_.uri=?)
Typically ugly framework generated SQL.
There are only two possibilities:
There is no table "jiresourcefolder", "JIResourceFolder" or any other variation in capitals.
The table was created with quotes to preserve its case and the query is not using quotes.
The following will work:
CREATE TABLE JiReSoRrCeFoLdEr ...
SELECT * FROM jiresourcefolder...
SELECT * FROM JIRESOURCEFOLDER...
SELECT * FROM JIresourceFolder...
Any unquoted table (or column) names are internally mapped to lower-case so will all match.
If however you quote a created table:
CREATE TABLE "JIResourceFolder"
SELECT * FROM "JIResourceFolder" -- works
SELECT * FROM JIResourceFolder -- doesn't
Check your database schema and see if you have this table and whether it is all lower-case. Then, check the documentation for your java framework(s) and see if there is some flag that controls quoting of database tables. It seems likely that the flag is set in one place and not in another.
I just had the same issue in Jasper Studio.
My problem was that a wrong Data Adapter (a DB that did not have such a table) was assigned to the Report.
I had switch to the Design window and select the right Data Adapter in the upper right of that window right beside "Settings".
Wondering if there is a way to query a SQL Server database and somehow format columns to omit commas in the data if there is any.
Reason for asking is I have 10000+ records and through out the data the varchar have data like 3,25% and other 1%.
I'd prefer not to alter the data in the original table thus asking if a select with other functions would do the trick.
I have thought about selecting all the data into a temp table and stripping the commas but that is a lot of work for every time I do the query.
Any info or if its is possible please reply.
Take a look at the REPLACE function:
SELECT REPLACE(YourColumn, ',', '')
FROM YourTable
Use SQL REPLACE :
REPLACE(YourField,',','')