I'm fairly new to PostgreSQL specially to the whole set of functions it has to manage JSONs. I have this json example where I can grab always one element but, I want to map it to a new array:
select '{"a": {"b":{"c": [{"id":"foo"},{"id":"fuu"}]}}}'::json#>'{a,b,c}';
column
-----------------------------
[{"id":"foo"},{"id":"fuu"}]
(1 row)
What I really want is:
[foo, fuu]
If you are using Postgres 12 or newer you can use a JSON path query:
select jsonb_path_query_array(the_column, '$.a.b.c[*].id')
from the_table
This assumes that the column is a jsonb column (which it should be). If it's not you need to cast it: the_column::jsonb
Related
I'm trying to extract data from a bytea column which stores JSON data in Postgres 11.9 version.
However, the my code is throwing an error:
ERROR: invalid input syntax for type json
DETAIL: Token "" is invalid.
CONTEXT: JSON data, line 1: ...
Here is the sample data:
create table EMPLOYEE (PAYMENT bytea,NAME character varying);
insert into EMPLOYEE
values ('[{"totalCode":{"code":"EMPLOYER_TAXES"},"totalValue":{"amount":122.5,"currencyCode":"USD"}},{"totalCode":{"code":"OTHER_PAYMENTS"},"totalValue":{"amount":0.0,"currencyCode":"USD"}},{"totalCode":{"code":"GROSS_PAY"},"totalValue":{"amount":1000.0,"currencyCode":"USD"}},{"totalCode":{"code":"TOTAL_HOURS"},"totalValue":{"amount":40.0}}]'::bytea,'Tom')
;
Here is my query:
SELECT *
FROM EMPLOYEE left outer join lateral
jsonb_array_elements(PAYMENT::text::jsonb) element1 on true ;
Please help me in accessing data from this array. Data is always JSON in format.
There was a restriction to use bytea for this column.
You are making your life unnecessary hard by storing JSON values in a bytea column. Just because this is the recommended way in Oracle, doesn't mean this is a good choice for Postgres.
The correct solution is to change that column to jsonb. You will have to have a DBMS specific layer in your application anyway as the actual functions and operators you are using are very different.
Having said that, you can get away with this awful choice by using the convert_from() method:
select e.name, element1.*
from employee e
left join lateral jsonb_array_elements(convert_from(PAYMENT, 'UTF-8')::jsonb) element1 on true;
I also think you should change your INSERT statement to do an explicit conversion from text to bytea so that you can be sure the correct encoding is used:
insert into employee (payment, name)
values (convert_to('[{...}]', 'UTF-8'),'Tom');
But again: the only correct solution is to change that column to jsonb (or least json)
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'm using PostgreSQL.
Is there any way to create index just on dictionary keys, not values.
For example imagine a jsonb column like:
select data from tablename where id = 0;
answer: {1:'v1', 2:'v2'}
I want to index on the key set (or key list) which is [1, 2]. To speed up queries like:
select count(*) from tablename where data ? '2';
As you can see in docs, there is a way for indexing the column entirely (keys + values):
CREATE INDEX idxgin ON api USING GIN (jdoc);
This is not good for me, considering that I store a large amount of data in values.
I tried this before:
CREATE INDEX test ON tablename (jsonb_object_keys(data));
The error was:
ERROR: set-returning functions are not allowed in index expressions
Also, I don't want to store keys in the dictionary as a value.
Can you help me?
Your example doesn't make much sense, as your WHERE clause isn't specifying a JSON operation, and your example output is not valid JSON syntax.
You can hide the set-returning function (and the aggregate) into an IMMUTABLE function:
create function object_keys(jsonb) returns text[] language SQL immutable as $$
select array_agg(jsonb_object_keys) from jsonb_object_keys($1)
$$;
create index on tablename using gin ( object_keys(data));
If you did it this way, you could then query it formulated like this:
select * from tablename where object_keys(data) #> ARRAY['2'];
You could instead make the function return a JSONB containing an array rather than returning a PostgreSQL text array, if you would rather query it that way:
select * from tablename where object_keys_jsonb(data) #> '"2"';
You can't use a ? formulation, because in JSONB that is specifically for objects not arrays. If you really wanted to use ?, you could instead write a function which keeps the object as an object, but converts all the values to JSON null or to empty string, so they take up less space.
I have a column of type TEXT which is supposed to represent a CLOB value and I'm trying to update its value like this:
UPDATE my_table SET my_column = TEXT 'Text value';
Normally this column is written and read by Hibernate and I noticed that values written with Hibernate are stored as integers (perhaps some internal Postgres reference to the CLOB data).
But when I try to update the column with the above SQL, the value is stored as a string and when Hibernate tries to read it, I get the following error: Bad value for type long : ["Text value"]
I tried all the options described in this answer but the result is always the same. How do I insert/update a TEXT column using SQL?
In order to update a cblob created by Hibernate you should use functions to handling large objects:
the documentation can be found in the following links:
https://www.postgresql.org/docs/current/lo-interfaces.html
https://www.postgresql.org/docs/current/lo-funcs.html
Examples:
To query:
select mytable.*, convert_from(loread(lo_open(mycblobfield::int, x'40000'::int), x'40000'::int), 'UTF8') from mytable where mytable.id = 4;
Obs:
x'40000' is corresponding to read mode (INV_WRITE)
To Update:
select lowrite(lo_open(16425, x'60000'::int), convert_to('this an updated text','UTF8'));
Obs:
x'60000' = INV_WRITE + INV_READ is corresponding to read and write mode (INV_WRITE + IV_READ).
The number 16425 is an example loid (large object id) which already exists in a record in your table. It's that integer number you can see as value in the blob field created by Hinernate.
To Insert:
select lowrite(lo_open(lo_creat(-1), x'60000'::int), convert_to('this is a new text','UTF8'));
Obs:
lo_creat(-1) generate a new large object a returns its loid
Given:
CREATE TABLE xmltest(xtxt xml);
And:
INSERT INTO xmltest values ('<EMP><NAME>Mike</NAME><HIREDATE>12-FEB-96</HIREDATE></EMP><EMP><NAME>Bob</NAME><HIREDATE>13-AUG-97</HIREDATE></EMP><EMP><NAME>Paul</NAME><HIREDATE>17-JUN-94</HIREDATE></EMP><EMP><NAME>Jim</NAME><HIREDATE>01-JUN-94</HIREDATE></EMP>');
Using the base functionality of Postgres 9.2, how would I write a SELECT statement that returned only the employee names, 1 name per row in the result set? Or would I have to write a function in PL/PGSQL to do that?
You can extract fields of interest into an array using the xpath function, and then from there you can use the unnest builtin to split this array into multiple rows:
SELECT unnest(xpath('//name', xtxt))
FROM xmltest;
(Slightly borrowed from this question)