I have an SQL database field that contains JSON type data stored.
-----------------------------
id | tags |
-----------------------------
1 | ['cat','dog'] |
2 | ['lion','cat','dog'] |
I want to select from this table by passing where condition as cat and get all the JSON fields. How would I do this?
Use the JSON_EXTRACT function as of MySQL 5.7.8. Extract from
https://dev.mysql.com/doc/refman/5.7/en/json.html#json-paths
A JSON path expression selects a value within a JSON document.
Path expressions are useful with functions that extract parts of or modify a JSON document, to specify where within that document to operate. For example, the following query extracts from a JSON document the value of the member with the name key:
mysql> SELECT JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name');
+---------------------------------------------------------+
| JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name') |
+---------------------------------------------------------+
| "Aztalan" |
+---------------------------------------------------------+
Note in the example they are inline creatinng a JSON object so for you
:'{"id": 14, "name": "Aztalan"}' would actually be your column value.
JSON manipulation in MySQL is slow. I suggest that you use REGEXP.
// get all rows having "cat" value
select * from animals_tbl
where tags regexp 'cat';
// get all rows based on multiple filters
select * from animals_tbl
where tags regexp 'lion|cat';
Related
I have a table with JSON data like this:
{"a": [{"color": "blue", "value": 15}, {"color": "red", "value": 30}]}
I need to get the "value" that is inside the same object of "blue".
I thought to use the code below:
SELECT JSON_EXTRACT(my_data, '$.a[0].value');
The problem is that the "blue" object can be in any index of the array.
So, is there a way to retrieve the index first and then i'll query using the right index?
UPDATE
The Barmar's answer works but it needs to wrap in JSON_UNQUOTE()
Use JSON_SEARCH() to find the path to blue.
SELECT JSON_EXTRACT(my_data, JSON_UNQUOTE(REPLACE(JSON_SEARCH(my_data, 'one', 'blue'), '.color', '.value')))
JSON_SEARCH will return a string like $.a[0].color. REPLACE changes that to $.a[0].value, then you extract that element.
DEMO
Here's an example of using JSON_TABLE():
select j.* from d, json_table(d.data, '$.a[*]' columns (
color varchar(20) path '$.color',
value int path '$.value')
) as j;
+-------+-------+
| color | value |
+-------+-------+
| blue | 15 |
| red | 30 |
+-------+-------+
You can then apply conditions in the WHERE clause, as if you had stored the data in a normal table.
select j.* from d, json_table(d.data, '$.a[*]' columns (
color varchar(20) path '$.color',
value int path '$.value')
) as j
where j.color = 'blue';
+-------+-------+
| color | value |
+-------+-------+
| blue | 15 |
+-------+-------+
This requires you to write a complex query like this EVERY TIME you query the JSON data.
One wonders if it would have been easier to store the JSON in a normal table from the start.
I often recommend to MySQL users that storing data as JSON makes more work for you, if you need to make SQL expressions to reference individual fields within the JSON. I wouldn't use JSON in these cases, I'd explode the JSON array into rows, and the JSON fields into columns of a set of normal tables. Then you can write simpler queries, you can optimize with indexes, and you can use constraints and data types properly.
JSON is the most easily misused feature of the recent MySQL releases.
Consider the following table
+-------------+--------------------------------------------------------------------------+
|company_name | products |
+-------------+--------------------------------------------------------------------------+
| comp1 | [{"name": "prod1","pending": false}, {"name": "prod2","pending": true}] |
+-------------+--------------------------------------------------------------------------+
Suppose I want to retrieve results based on the the value of "name" field inside "products" column, for ex: if "pending" = "true", then display the company_name and also the product name of the particular JSON object inside the List or Array.
Result should look something like,
+-------------+-------------------------------+
|company_name | product_name |
+-------------+-------------------------------+
| comp1 | prod2 |
+-------------+-------------------------------+
You should use a program in python, perl etc that retrieve json and convert it to array and you print the column of array that you need.
use index to get value $[ index ]
Code will be like this:
Select company_name,json_extract(products,'$[1].name') product_name from table where json_extract(products,'$[1].pending')='false' ;
Note: create a dummy table with numbers and join it for index
So I made this system to store custom objects with custom fields for an app that I'm developing. First I have object_def where I save the object definitions:
id | name | fields
------------------------------------------------------------
101 | Group 1 | [{"name": "Title", "id": "AbCdE123"}, ...]
102 | Group 2 | [{"name": "Name", "id": "FgHiJ456"}, ...]
So we have ID (INT), name (VARCHAR) and fields (LONGTEXT). In fields are the object fields like this: {id: string, type: string, name: string}[].
Now In the object table, I have this:
id | object_def_id | object_values
------------------------------------------------------------
235 | 101 | {"AbCdE123": "The Object", ... }
236 | 102 | {"FgHiJ456": "John Perez", ... }
Where object_values is a LONGTEXT also. With that system, I'm able to show the objects on a table in my app using JSON.parse().
Now I've learned that there is a JSON type in MySQL and I want it to use it to do queries and stuff (I'm really new to this).
I've changed the LONGTEXT to JSON and now I wanted to do a SELECT that show the results like this:
#Select objects in group 1:
id | group | Title | ... | other_custom_field
-------------------------------------------------------
235 | Group 1 | The Object | ... | other_custom_value
#Select objects in group 2:
id | group | Name | ... | other_custom_field
-------------------------------------------------------
236 | Group 2 | John Perez | ... | other_custom_value
Id, then group name (I can do this with INNER JOIN) and then all the custom fields with the respective values.
Is this possible? How can I achieve this (hopefully without changing my database structure)? I'm learning MySQL, SQL and databases as I go so I really appreciate your help. Thanks!
Problems I see with your design:
Incorrect JSON format.
[{name: 'Title', id: 'AbCdE123'}, ...]
Should be:
[{"name": "Title", "id": "AbCdE123"}, ...]
You should use the JSON data type instead of LONGTEXT, because JSON will at least reject invalid JSON syntax.
Setting column headings based on data. You can't do this in SQL. Columns and headings must be fixed at the time you prepare the query. You can't do an SQL query that changes its own column headings.
Your object def has an array of attributes, but there's no way in MySQL 5.7 to loop over the "rows" of a JSON array. You'll need to use the JSON_TABLE() in MySQL 8.0.
That will get you closer to being able to look up object values, but then you'll still have to pivot the data into the result set you describe, with one attribute in each column, as if the data had been stored in a traditional way. But SQL doesn't allow you to do dynamic pivoting in a single query. You can't make an SQL query that dynamically grows its own select-list based on the data it finds.
This all makes me wonder...
Why don't you just store the data in the traditional way?
Create a table per object type. Add one column to that table per attribute. That way you get column names. You get column types. You get column constraints — for example, how would you simulate NOT NULL or UNIQUE in your current system?
If you don't want to use SQL, then don't. There are alternatives, like document databases or key/value databases. But don't torture poor SQL by using it to implement an Inner-Platform.
I have the following table:
+-------------+----------------+
| id | server |
+-------------+----------------+
| 1 | ["1", "15"] |
+-------------+----------------+
I need to get only value that is grather that 1 so in above example i need to get from output only 15
I try using this:
SELECT
JSON_EXTRACT(server, "$[*]") as server
FROM streams
WHERE JSON_EXTRACT(server, "$[*]") != JSON_QUOTE('1')
AND id=1;
But i always get ["1", "15"] and need to get ["15"].
Unfortunately, you can't do this with MySQL's JSON_EXTRACT and JSON_SEARCH functions as they perform extraction and exact matching (not comparison) respectively. So, you have two options:
Normalise the table and have server values into a new column (recommended)
Fetch all the values and perform the filtering in service layer
I added this:
SELECT CASE WHEN
JSON_UNQUOTE(JSON_SEARCH(server, 'all', 1)) IS NULL THEN
JSON_REMOVE(server, '$."1"')
ELSE
JSON_REMOVE(server, JSON_UNQUOTE(JSON_SEARCH(server, 'one', 1)))
END AS server
FROM streams WHERE id=2 AND server NOT LIKE '%[]%';
Now it works but if ["1"] is only 1 in json column i get []...a added NOT LIKE '%[]%' but it prints out always []...where i need to add to get no results found from mysql?
I'm storing permissions into DB with Array JSON String, and i want select them by permission specific permission. at this time I'm selecting them like this:
1 | Dog | [3,4]
2 | Cat | [33,4]
3 | Tiger | [5,33,4]
4 | wolf | [3,5]
SELECT * FROM `pages` WHERE access REGEXP '([^"])3([^"])'
it works but not as it should work. This query gives me all records which contains 3 but also it gives which contains 33. my question is how i must format my regexp to get row by specific value into json string.
p.s i have mysql 5.5 so as i know on this version json functions is not supported
If you only have numbers in the fields, you can alter your regexp to only take values where the string you are looking for (here the '3') does not have another number immediately close to it :
SELECT * FROM `pages` WHERE access REGEXP '([^"0-9])3([^"0-9])'
REGEXP '[[:<:]]3[[:>:]]'
That is, use the "word boundary" thingies.