I've got a Postgres ORDER BY issue with the following table:
em_code name
EM001 AAA
EM999 BBB
EM1000 CCC
To insert a new record to the table,
I select the last record with SELECT * FROM employees ORDER BY em_code DESC
Strip alphabets from em_code usiging reg exp and store in ec_alpha
Cast the remating part to integer ec_num
Increment by one ec_num++
Pad with sufficient zeors and prefix ec_alpha again
When em_code reaches EM1000, the above algorithm fails.
First step will return EM999 instead EM1000 and it will again generate EM1000 as new em_code, breaking the unique key constraint.
Any idea how to select EM1000?
Since Postgres 9.6, it is possible to specify a collation which will sort columns with numbers naturally.
https://www.postgresql.org/docs/10/collation.html
-- First create a collation with numeric sorting
CREATE COLLATION numeric (provider = icu, locale = 'en#colNumeric=yes');
-- Alter table to use the collation
ALTER TABLE "employees" ALTER COLUMN "em_code" type TEXT COLLATE numeric;
Now just query as you would otherwise.
SELECT * FROM employees ORDER BY em_code
On my data, I get results in this order (note that it also sorts foreign numerals):
Value
0
0001
001
1
06
6
13
۱۳
14
One approach you can take is to create a naturalsort function for this. Here's an example, written by Postgres legend RhodiumToad.
create or replace function naturalsort(text)
returns bytea language sql immutable strict as $f$
select string_agg(convert_to(coalesce(r[2], length(length(r[1])::text) || length(r[1])::text || r[1]), 'SQL_ASCII'),'\x00')
from regexp_matches($1, '0*([0-9]+)|([^0-9]+)', 'g') r;
$f$;
Source: http://www.rhodiumtoad.org.uk/junk/naturalsort.sql
To use it simply call the function in your order by:
SELECT * FROM employees ORDER BY naturalsort(em_code) DESC
The reason is that the string sorts alphabetically (instead of numerically like you would want it) and 1 sorts before 9.
You could solve it like this:
SELECT * FROM employees
ORDER BY substring(em_code, 3)::int DESC;
It would be more efficient to drop the redundant 'EM' from your em_code - if you can - and save an integer number to begin with.
Answer to question in comment
To strip any and all non-digits from a string:
SELECT regexp_replace(em_code, E'\\D','','g')
FROM employees;
\D is the regular expression class-shorthand for "non-digits".
'g' as 4th parameter is the "globally" switch to apply the replacement to every occurrence in the string, not just the first.
After replacing every non-digit with the empty string, only digits remain.
This always comes up in questions and in my own development and I finally tired of tricky ways of doing this. I finally broke down and implemented it as a PostgreSQL extension:
https://github.com/Bjond/pg_natural_sort_order
It's free to use, MIT license.
Basically it just normalizes the numerics (zero pre-pending numerics) within strings such that you can create an index column for full-speed sorting au naturel. The readme explains.
The advantage is you can have a trigger do the work and not your application code. It will be calculated at machine-speed on the PostgreSQL server and migrations adding columns become simple and fast.
you can use just this line
"ORDER BY length(substring(em_code FROM '[0-9]+')), em_code"
I wrote about this in detail in this related question:
Humanized or natural number sorting of mixed word-and-number strings
(I'm posting this answer as a useful cross-reference only, so it's community wiki).
I came up with something slightly different.
The basic idea is to create an array of tuples (integer, string) and then order by these. The magic number 2147483647 is int32_max, used so that strings are sorted after numbers.
ORDER BY ARRAY(
SELECT ROW(
CAST(COALESCE(NULLIF(match[1], ''), '2147483647') AS INTEGER),
match[2]
)
FROM REGEXP_MATCHES(col_to_sort_by, '(\d*)|(\D*)', 'g')
AS match
)
I thought about another way of doing this that uses less db storage than padding and saves time than calculating on the fly.
https://stackoverflow.com/a/47522040/935122
I've also put it on GitHub
https://github.com/ccsalway/dbNaturalSort
The following solution is a combination of various ideas presented in another question, as well as some ideas from the classic solution:
create function natsort(s text) returns text immutable language sql as $$
select string_agg(r[1] || E'\x01' || lpad(r[2], 20, '0'), '')
from regexp_matches(s, '(\D*)(\d*)', 'g') r;
$$;
The design goals of this function were simplicity and pure string operations (no custom types and no arrays), so it can easily be used as a drop-in solution, and is trivial to be indexed over.
Note: If you expect numbers with more than 20 digits, you'll have to replace the hard-coded maximum length 20 in the function with a suitable larger length. Note that this will directly affect the length of the resulting strings, so don't make that value larger than needed.
I am trying to run a query like this
SELECT group, sum("a column with spaces") FROM x GROUP BY group
Unfortunately, I get the error function sum(text) does not exist. It appears to be interpreting my quoted identifier "a column with spaces" as a text string instead of column name. How can I specify that this is an identifier?
I found a way to trick it into parsing it as an identifier -- prefix it with the table identifier or alias:
SELECT group, sum(t."a column with spaces") FROM table_name t GROUP BY group;
Double-quotes are actually the right way to identify columns, but in this case it won't work.
I managed to apply an aggregate function renaming the column and removing its white spaces.
CREATE TABLE example (
"column with space" INTEGER
);
INSERT INTO example VALUES (1), (2);
SELECT SUM(column_with_space)
FROM (
SELECT "column with space" AS column_with_space
FROM example
) AS example_query;
Got result:
sum
3
I am using PostgreSQL 11.9
I have a table containing a jsonb column with arbitrary number of key-values. There is a requirement when we perform a search to include all values from this column as well. Searching in jsonb is quite slow so my plan is to create a trigger which will extract all the values from the jsonb column:
select t.* from app.t1, jsonb_each(column_jsonb) as t(k,v)
with something like this. And then insert the values in a newly created column in the same table so I can use this column for faster searches.
My question is what type would be most suitable for storing the keys and then searchin within them. Currently the search looks like this:
CASE
WHEN something IS NOT NULL
THEN EXISTS(SELECT value FROM jsonb_each(column_jsonb) WHERE value::text ILIKE search_term)
END
where the search_term is what the user entered from the front end.
This is not going to be pretty, and normalizing the data model would be better.
You can define a function
CREATE FUNCTION jsonb_values_to_string(
j jsonb,
separator text DEFAULT ','
) RETURNS text LANGUAGE sql IMMUTABLE STRICT
AS 'SELECT string_agg(value->>0, $2) FROM jsonb_each($1)';
Then you can query like
WHERE jsonb_values_to_string(column_jsonb, '|') ILIKE 'search_term'
and you can define a trigram index on the left hand side expression to speed it up.
Make sure that you choose a separator that does not occur in the data or the pattern...
I would like to know how I can insert regular expression in a table column in a PostgreSQl table.
For example I have column called "rule" in a table where I need to store the expression ^[0-9]+$. I tried:
insert into rule_master(rule)
values('^[0-9]+$') where rule_id='7'
But I am getting error syntax near where is wrong. I tried this with and with out single quotes. Please suggest me a solution.
It appears you want to UPDATE an existing record. In that case you should do:
UPDATE rule_master
SET rule = '^[0-9]+$'
WHERE rule_id = '7';
But if this is indeed a new record and you want to INSERT that regex with the value of "rule_id" then do:
INSERT INTO rule_master(rule_id, rule)
VALUES ('7', '^[0-9]+$');
How to use upper() in where clause. Below query is giving error:
http://kdbserver:5001/?select from table where upper(cola) = `ABC
Please suggest how to query
N.B.:Cola is a column
http://kdbserver:5001/?select upper(cola) from table <-- is working fine.
Try upper[cola]='ABC'.
Round brackets are not used for function arguments, they are used for precedence etc. Square brackets are used in function arguments.
The reason round brackets worked in the second case is because the parser simply ignored them. Would be the same as select upper cola from table
In your first case you have effectively done select from table where upper (cola='ABC') rather than select from table where (upper cola)='ABC'.