Suppose I have the following MySQL table structure:
==========================================================
| id | name | address |
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| 1 | Dawn | {"state": "Maryland", "city": "Annapolis"} |
| 2 | Pablo| {"state": "Ohio", "city": "Columbus"} |
The address column is of json type. I use the bookshelf and the knex ORM in my application, I need to do query so that it will fetch name and the state name without city.
My plain SQL query will look like this:
select name, address->"$.state"
from user
OR
select name, json_extract(address, "$.state")
from user
But when I do it using Bookshelf:
user.select('name', 'address->"$.state"').fetch().then(....)
I'm getting an invalid error in SQL command due to the quote and backtick format.
The SQL generated using bookshelf is as below:
select 'address->\" '.'state\" ', 'name' from `user.
Any suggestions to avoid the backtick mark issue around Dot(.) character ?? Or some other way of approach??
PS: This just an example
You can generate those queries like this:
// select name, address->"$.state" from user
knex('user').select('name', knex.raw('??->"$.state"', ['address']))
// select name, json_extract(address, "$.state") from user
knex('user').select('name', knex.raw('json_extract(??, "$.state")', ['address']))
Related
I have a table which's name is users in my MySQL database, and I am using this DB with Ruby on Rails application with ORM structure for years. The table has id field and this field is configured as AI (auto-increment), BIGINT.
Example of my users table;
+----+---------+
| id | name |
+----+---------+
| 1 | John |
| 2 | Tommy |
| 3 | ... |
| 4 | ... |
| 5 | ... |
| 6 | ... |
+----+---------+
The problem I am facing is when I execute the following query I get unexpected rows.
SELECT * FROM users WHERE id = '1AW3F4SEFR';
This query is returning the exact same value with the following query,
SELECT * FROM users WHERE id = 1;
I do not know why SQL let me use strings in WHERE clause on a data type INT. And as we can see from the example, my DB converts the strings I gave to the integer at position 0. I mean, I search for 1AW3F4SEFR and I expect not to get any result. But SQL statement returns the results for id = 1.
In Oracle SQL, the behavior of this exact same query is completely different. So, I believe there is something different on MySQL. But I am not sure about what causes this.
As has been explained in the request comments, MySQL has a weird way of converting strings to numbers. It simply takes as much of a string from the left as is numeric and ignores the rest. If the string doesn't start with a number the conversion defaults to 0.
Examples: '123' => 123, '12.3' => 12.3, '.123' => 0.123, '12A3' => 12, 'A123' => 0, '.1A1.' => 0.1
Demo: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=55cd18865fad4738d03bf28082217ca8
That MySQL doesn't raise an error here as other DBMS do, can easily lead to undesired query results that get a long time undetected.
The solution is easy though: Don't let this happen. Don't compare a numeric column with a string. If the ID '1AW3F4SEFR' is entered in some app, raise an error in the app or even prevent this value from being entered. When running the SQL query, make sure to pass a numeric value, so '1AW3F4SEFR' cannot even make it into the DBMS. (Look up how to use prepared statements and pass parameters of different types to the database system in your programming language.)
If for some reason you want to pass a string for the ID instead (I cannot think of any such reason though) and want to make your query fail-safe by not returning any row in case of an ID like '1AW3F4SEFR', check whether the ID string represents an integer value in the query. You can use REGEXP for this.
SELECT * FROM users WHERE id = #id AND #id REGEXP '^[0-9]+$';
Thus you only consider integer ID strings and still enable the DBMS to use an index when looking up the ID.
Demo: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=56f8ee902342752933c20b8762f14dbb
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 table region with fields
id | name | dates
Sample data
1 | local | "2018-01-01", "2018-01-02", "2018-01-03"
I want a query like this
SELECT * FROM region WHERE "2018-01-02" in (region.dates)
but this does not work. I do not use json data in this case. How can I change it?
(My)SQL doesn't work like that as it will see region.dates as a simple string. In which case, you can do SELECT * FROM region WHERE dates LIKE '%"2018-01-02"%';
However, a better solution would be to devolve that column into another table.
I have a table that looks like this
+------+------------------------------------+
| id | details |
+------+------------------------------------+
| 1 | {"price":"24.99","currency":"USD"} |
+------+------------------------------------+
Is it possible to, with a single MySQL select statement, obtain the value of price 24.99?
Yes, you can using JSON_EXTRACT
It probably should be like:
SELECT JSON_EXTRACT(details, "$.price")
FROM table_name
or another form:
SELECT details->"$.price"
FROM table_name
(I don't have MySql to test it)
Note that the price in your JSON stored as a string, not a number and you probably would want to cast it to a DECIMAL.
I need to export a csv file from phpmyadmin that is filtered to some degree.
My Table looks like this
ID | Name | Email | Price
29817 | Firstname LastName | Random#email.com |
{"subtotal":{"1":774,"0":730.18867924528},
"discount":{"1":70,"0":66.037735849057},
"shipping":{"1":59,"0":55.660377358491},
"handling":{"1":0,"0":0},
"printer":{"1":288.75,"0":231}
}
I Need to select the subtotal of this this column and i've tried multiple ways to do this and ofcourse have googled around a lot. I can't seem to find any good information about this and was wondering how you can do this with only SQL no PHP
So far i've tried this
SELECT name, email, id
FROM order_pending
WHERE country = 'se'
AND price['subtotal'] > 2000
and Also This
SELECT name, email, id
FROM order_pending
WHERE country = 'se'
AND price.subtotal > 2000
I get syntax error in the sql and i don't know how to do a correct search inside an array.