I've a table with JSON column and want to select rows where JSON key 'k' has value 'value'. Json may consist of several pairs of [K,V].
[
{"k":"esr:code","v":"800539"},
{"k":"lit","v":"yes"},
{"k":"name","v":"5 ΠΊΠΌ"},
{"k":"railway","v":"halt"},
{"k":"uic_ref","v":"2040757"}
]
I tried to use the next query, but it's wrong.
SELECT *
FROM public.node
where ((node.tags)::json->>'k' like 'name')
How I can fix it, if it's possible?)
Where node - table name, tags - json column.
You can use the JSONB contains operator #>
SELECT *
FROM public.node
where node.tags #> '[{"k","name"}]';
This will do an exact match against name. Your usage of like might indicate you are looking for a partial match - however as your like condition doesn't use a wildcard it's the same as =.
This assumes that tags is defined as jsonb (which it should be). If it's not you need to cast it: node.tags::jsonb
Related
I am working on data in postgresql as in the following mytable with the fields id (type int) and val (type json):
id
val
1
"null"
2
"0"
3
"2"
The values in the json column val are simple JSON values, i.e. just strings with surrounding quotes and have no key.
I have looked at the SO post How to convert postgres json to integer and attempted something like the solution presented there
SELECT (mytable.val->>'key')::int FROM mytable;
but in my case, I do not have a key to address the field and leaving it empty does not work:
SELECT (mytable.val->>'')::int as val_int FROM mytable;
This returns NULL for all rows.
The best I have come up with is the following (casting to varchar first, trimming the quotes, filtering out the string "null" and then casting to int):
SELECT id, nullif(trim('"' from mytable.val::varchar), 'null')::int as val_int FROM mytable;
which works, but surely cannot be the best way to do it, right?
Here is a db<>fiddle with the example table and the statements above.
Found the way to do it:
You can access the content via the keypath (see e.g. this PostgreSQL JSON cheatsheet):
Using the # operator, you can access the json fields through the keypath. Specifying an empty keypath like this {} allows you to get your content without a key.
Using double angle brackets >> in the accessor will return the content without the quotes, so there is no need for the trim() function.
Overall, the statement
select id
, nullif(val#>>'{}', 'null')::int as val_int
from mytable
;
will return the contents of the former json column as int, respectvely NULL (in postgresql >= 9.4):
id
val_int
1
NULL
2
0
3
2
See updated db<>fiddle here.
--
Note: As pointed out by #Mike in his comment above, if the column format is jsonb, you can also use val->>0 to dereference scalars. However, if the format is json, the ->> operator will yield null as result. See this db<>fiddle.
I have a column in my Postgres database that stores jsonb type values. Some of these values are raw strings (not a list or dictionary). I want to be able to perform a regex search on this column, such as
select * from database where jsonb_column::text ~ regex_expression.
The issue is that for values that are already strings, converting from jsonb to text adds additional escaped double quotes at the beginning and end of the value. I don't want these included in the regex query. I understand why Postgres does this, but if, say we assume all values stored in the jsonb field were jsonb strings, is there a work around? I know you can use ->> to get a value out of a jsonb dictionary, but can't figure out a solution for just jsonb strings on their own.
Once I figure out how to make this query in normal Postgres, I want to translate it into Peewee. However, any and all help with even just the initial query would be appreciated!
Just cast the json to text. Here is an example:
class Reg(Model):
key = CharField()
data = BinaryJSONField()
class Meta:
database = db
for i in range(10):
Reg.create(key='k%s' % i, data={'k%s' % i: 'v%s' % i})
# Find the row that contains the json string "k1": "v1".
expr = Reg.data.cast('text').regexp('"k1": "v1"')
query = Reg.select().where(expr)
for row in query:
print(row.key, row.data)
Prints
k1 {'k1': 'v1'}
To extract a plain string (string primitive without key name) from a JSON value (json or jsonb), you can extract the "empty path" like:
SELECT jsonb '"my string"' #>> '{}';
This also works for me (with jsonb but not with json), but it's more of a hack:
SELECT jsonb '"my string"' ->> 0
So:
SELECT * FROM tbl WHERE (jsonb_column #>> '{}') ~ 'my regex here';
I have a table, for example writing in psql. This table has a column json (text type). It contains text like this:
writing:[{"variableName":variableValue ...}]
variableValues are different types, including text ,bigint and date.
I want to get all rows from writing where variableName has the value 2.
I'm using this select:
select * from writing where json::json->>'variableName' = '2' limit 5
This select returns me 0 rows, but there are a lot of data in this table, which should pass this condition. Any idea what is wrong, or maybe you have better statement.
Im using limit 5 because need just 5 rows.
You'll have to prepend a { and append a } to make it a JSON like you intend. As it is, it will become a single JSON string.
Then you'll have to access the attribute as
('{' || json || '}')::json->'writing'->1->>'variableName'
I have a postgresql database with a table called choices, in the choices table I have a column called json that contains JSON entries, for example: [1,2,3]
I need a query that returns all entires that contains a specific value.
For example I have the following entries:
[1,2,3] [6,7,1] [4,5,2]
I want to get all entries that contain the value 1 so it would return:
[1,2,3]
[6,7,1]
Thanks,
demo: db<>fiddle
The json_array_elements_textfunctions expands the json arrays into one row each element (as text). With that you can filter it by any value you like.
SELECT
json_data
FROM choices, json_array_elements_text(json_data) elem
WHERE value = '1'
Documentation: JSON functions
Please notice that "json" is a the name for the json type in PostgreSQL. You should better rename your column to avoid some conflicts. (I called mine json_data)
I have some data in a postgres table that is a string representation of an array of json data, like this:
[
{"UsageInfo"=>"P-1008366", "Role"=>"Abstract", "RetailPrice"=>2, "EffectivePrice"=>0},
{"Role"=>"Text", "ProjectCode"=>"", "PublicationCode"=>"", "RetailPrice"=>2},
{"Role"=>"Abstract", "RetailPrice"=>2, "EffectivePrice"=>0, "ParentItemId"=>"396487"}
]
This is is data in one cell from a single column of similar data in my database.
The datatype of this stored in the db is varchar(max).
My goal is to find the average RetailPrice of EVERY json item with "Role"=>"Abstract", including all of the json elements in the array, and all of the rows in the database.
Something like:
SELECT avg(json_extract_path_text(json_item, 'RetailPrice'))
FROM (
SELECT cast(json_items to varchar[]) as json_item
FROM my_table
WHERE json_extract_path_text(json_item, 'Role') like 'Abstract'
)
Now, obviously this particular query wouldn't work for a few reasons. Postgres doesn't let you directly convert a varchar to a varchar[]. Even after I had an array, this query would do nothing to iterate through the array. There are probably other issues with it too, but I hope it helps to clarify what it is I want to get.
Any advice on how to get the average retail price from all of these arrays of json data in the database?
It does not seem like Redshift would support the json data type per se. At least, I found nothing in the online manual.
But I found a few JSON function in the manual, which should be instrumental:
JSON_ARRAY_LENGTH
JSON_EXTRACT_ARRAY_ELEMENT_TEXT
JSON_EXTRACT_PATH_TEXT
Since generate_series() is not supported, we have to substitute for that ...
SELECT tbl_id
, round(avg((json_extract_path_text(elem, 'RetailPrice'))::numeric), 2) AS avg_retail_price
FROM (
SELECT *, json_extract_array_element_text(json_items, pos) AS elem
FROM (VALUES (0),(1),(2),(3),(4),(5)) a(pos)
CROSS JOIN tbl
) sub
WHERE json_extract_path_text(elem, 'Role') = 'Abstract'
GROUP BY 1;
I substituted with a poor man's solution: A dummy table counting from 0 to n (the VALUES expression). Make sure you count up to the maximum number of possible elements in your array. If you need this on a regular basis create an actual numbers table.
Modern Postgres has much better options, like json_array_elements() to unnest a json array. Compare to your sibling question for Postgres:
Can get an average of values in a json array using postgres?
I tested in Postgres with the related operator ->>, where it works:
SQL Fiddle.