I have a nullable JSON MySQL 5.7 field which I am finding almost impossible to get working.
Example query:
UPDATE `json_test` SET `data` = JSON_SET(`data`, '$.a', 1)
If the field data is NULL already, it won't update.
If it's { "a" : 2 }, then it'll update correctly to 1. I need it to set if not set already, which is what JSON_SET is supposed to do.
Any ideas what's happening?
1) An alternative is to check for null and return an valid empty JSON set ({}) to JSON_SET in those situations, so it just puts in the new data.
UPDATE json_test SET data = JSON_SET(IFNULL(data,'{}' ), '$.a', 1)
2) Finally, another option would be for the data specification to have a default value of {}, ex.
`dataJson TEXT DEFAULT '{}',`
I prefer the first option I presented as I like leaving fields NULL until I need them to have data but then I expect them to start packing in the JSON data immediately!
Updating the entire table for that is an overkill and changing the table definition as well.
This should have no noticeable performance impact:
UPDATE `json_test` SET `data` = JSON_SET(COALESCE(`data`,'{}'), '$.a', 1)
Explanation:
JSON_SET needs a full processing of the column in any case, so it will be evaluated for validity, parsed, etc.
The COALESCE changes a NULL field to an empty JSON object, so the json will be valid and the SET will be successful.
You probably won't be able to measure a performance difference.
it's not supposed to work with nulls
Otherwise, a path/value pair for a nonexisting path in the document is
ignored and has no effect.
Now mysql doesn't let you use a subquery on the same table that's being updated, but you could probably stil solve this with an UPDATE JOIN using CASE/WHEN but I am too lazy so I leave you with a two query solution.
UPDATE `json_test` SET `data` = JSON_SET(`data`, '$.a', 1) WHERE data IS NOT NULL;
UPDATE `json_test` SET `data` = JSON_OBJECT('$.a', 1) WHERE data IS NULL;
Related
The SQLite JSON1 extension has some really neat capabilities. However, I have not been able to figure out how I can update or insert individual JSON attribute values.
Here is an example
CREATE TABLE keywords
(
id INTEGER PRIMARY KEY,
lang INTEGER NOT NULL,
kwd TEXT NOT NULL,
locs TEXT NOT NULL DEFAULT '{}'
);
CREATE INDEX kwd ON keywords(lang,kwd);
I am using this table to store keyword searches and recording the locations from which the search was ininitated in the object locs. A sample entry in this database table would be like the one shown below
id:1,lang:1,kwd:'stackoverflow',locs:'{"1":1,"2":1,"5":1}'
The location object attributes here are indices to the actual locations stored elsewhere.
Now imagine the following scenarios
A search for stackoverflow is initiated from location index "2". In this case I simply want to increment the value at that index so that after the operation the corresponding row reads
id:1,lang:1,kwd:'stackoverflow',locs:'{"1":1,"2":2,"5":1}'
A search for stackoverflow is initiated from a previously unknown location index "7" in which case the corresponding row after the update would have to read
id:1,lang:1,kwd:'stackoverflow',locs:'{"1":1,"2":1,"5":1,"7":1}'
It is not clear to me that this can in fact be done. I tried something along the lines of
UPDATE keywords json_set(locs,'$.2','2') WHERE kwd = 'stackoverflow';
which gave the error message error near json_set. I'd be most obliged to anyone who might be able to tell me how/whether this should/can be done.
It is not necessary to create such complicated SQL with subqueries to do this.
The SQL below would solve your needs.
UPDATE keywords
SET locs = json_set(locs,'$.7', IFNULL(json_extract(locs, '$.7'), 0) + 1)
WHERE kwd = 'stackoverflow';
I know this is old, but it's like the first link when searching, it deserves a better solution.
I could have just deleted this question but given that the SQLite JSON1 extension appears to be relatively poorly understood I felt it would be more useful to provide an answer here for the benefit of others. What I have set out to do here is possible but the SQL syntax is rather more convoluted.
UPDATE keywords set locs =
(select json_set(json(keywords.locs),'$.**N**',
ifnull(
(select json_extract(keywords.locs,'$.**N**') from keywords where id = '1'),
0)
+ 1)
from keywords where id = '1')
where id = '1';
will accomplish both of the updates I have described in my original question above. Given how complicated this looks a few explanations are in order
The UPDATE keywords part does the actual updating, but it needs to know what to updatte
The SELECT json_set part is where we establish the value to be updated
If the relevant value does not exsit in the first place we do not want to do a + 1 on a null value so we do an IFNULL TEST
The WHERE id = bits ensure that we target the right row
Having now worked with JSON1 in SQLite for a while I have a tip to share with others going down the same road. It is easy to waste your time writing extremely convoluted and hard to maintain SQL in an effort to perform in-place JSON manipulation. Consider using SQLite in memory tables - CREATE TEMP TABLE... to store intermediate results and write a sequence of SQL statements instead. This makes the code a whole lot eaiser to understand and to maintain.
My users table contains a metadata column of type json.
Now, I want to add new metadata to a user while preserving existing values.
So I'm using the || operator to merge 2 JSON objects:
UPDATE users
SET metadata = metadata::jsonb || '{"test": true}'::jsonb
WHERE id=...
RETURNING *;
Everything works fine when there are already some existing metadata.
However, when the previous value is NULL then the update doesn't work. The metadata after update is still NULL.
How can I improve my query so that it sets the new JSON object when the previous value is NULL or merges the previous and new values otherwise?
add coalesce:
UPDATE users
SET metadata = coalesce(metadata::jsonb,'{}'::jsonb) || '{"test": true}'::jsonb
WHERE id=...
RETURNING *;
it works similar like with normal strings NULL || something is always NULL
I'm having some odd SQL problems when inserting new rows into a table. I have set some columns to NULL, as I have with another table in my database. Obviously when no data is passed through on insertion it should enter NULL into the record, however currently it is not.
I have checked all settings in comparison with my other table (which is inserting records as NULL correctly) but can't find the issue. The columns appear as below, in both tables.
`statement_1` varchar(255) DEFAULT NULL,
No data is being pasted through (so not a blank space issue). Can anyone suggest why one table is doing as expected but the other is not?
Using below as the insert statement
$statement_a = "INSERT INTO statements (ucsid, statement_1, statement_2, statement_3, statement_4, statement_5, statement_6, statement_7, statement_8, statement_9, statement_10) VALUES (:ucsid, :statement_1, :statement_2, :statement_3, :statement_4, :statement_5, :statement_6, :statement_7, :statement_8, :statement_9, :statement_10)";
$q_a = $this->db_connection->prepare($statement_a);
$q_a->execute(array(':ucsid'=>$ucsid,
':statement_1'=>$statement_1,
':statement_2'=>$statement_2,
':statement_3'=>$statement_3,
':statement_4'=>$statement_4,
':statement_5'=>$statement_5,
':statement_6'=>$statement_6,
':statement_7'=>$statement_7,
':statement_8'=>$statement_8,
':statement_9'=>$statement_9,
':statement_10'=>$statement_10));
I can not add comments as I am new:
Try a simple INSERT statement using NOT phpmyadmin. Try
http://www.heidisql.com/ OR https://www.mysql.com/products/workbench/
INSERT INTO statements (ucsid) VALUES (123)
INSERT INTO statements (ucsid, statement_1) VALUES (123, NULL)
In both cases the statement_1 should be NULL. Which in your case most likely is not. However that would tell the problem lies in the database table and NOT with php or the php execute method you are using.
Also is the statement_1 field defined as NOT NULL and the default set as NULL? which can not happen.
Try recreating a new database and a new table with no records and than try inserting NULL as values as a test.
Also can you post the SQL of your database and table with Character Set and Collation
I've fixed the issue by ensuring that NULL is passed through the functions if nothing has been inserted by using the following code
if($_POST['statement_1'] == '') { $statement_1 = NULL; } else { $statement_1 = $_POST['statement_1']; }
Here the value passed by the varriable $statement_1 will be ""
Try this query SELECT * FROM my_table WHERE statement_1 ="".You will get rows.
Which means you are assigning some values to $statement_1 else it should be null.
Check your code. Hope this helps
I'm building a site in Laravel.
I have foreign key constraints set up among InnoDB tables.
My problem is that if i don't select a value in a, say, select box, the framework tries to insert or update a record in a table with '' (empty string). Which causes a MySQL error as it cannot find the equivalent foreign key value in the subtables.
Is there some elegant way to force the insertion of NULL in the foreign key fields other than checking out every single field? Or to force MySQL to accept '' as a "null" foreign key reference?
In other words: I have a, say, SELECT field with first OPTION blank. I leave the blank OPTION chosen. When I submit, an empty string '' is passed. In MySQL apparently I can do UPDATE table SET foreignKey=NULL but not UPDATE table SET foreignKey=''. It does not "convert" to NULL. I could check the fields one by one but and convert '' to NULL for every foreign key, maybe specifying all of them in an array, I was wondering if there's a more streamlined way to do this.
Maybe have to change my ON UPDATE action (which is not set) in my DB schema?
Edit: the columns DO accept the NULL value, the problem is in how the framework or MySQL handle the "empty value" coming from the HTML. I'm not suggesting MySQL "does it wrong", it is also logical, the problem is that you can't set a "NULL" value in HTML, and I would like to know if there's an elegant way to manage this problem in MySQL or Laravel.
In other words, do I have to specify manually the foreign keys and construct my query accordingly or is there another robust and elegant way?
My code so far for the model MyModel:
$obj = new MyModel;
$obj->fill(Input::all())); // can be all() or a subset of the request fields
$obj->save();
At least since v4 of Laravel (and Eloquent models), you can use mutators (aka setters) to check if a value is empty and transform it to null, and that logic is nicely put in the model :
class Anything extends \Eloquent {
// ...
public function setFooBarAttribute($value) {
$this->attributes['foo_bar'] = empty($value)?null:$value;
}
}
You can check out the doc on mutators.
I've been oriented by this github issue (not exactly related but still).
Instead of using
$obj = new MyModel;
$obj->fill(Input::all())); // can be all() or a subset of the request fields
$obj->save();
Use
$obj = new MyModel;
$obj->fieldName1 = Input::get('formField1');
$obj->fieldName2 = Input::has('formField2') && Input::get('formField2') == 'someValue' ? Input::get('formField2') : null;
// ...
$obj->save();
And make sure your database field accepts null values. Also, you can set a default value as null from the database/phpmyadmin.
You must remove the "not null" attribute from the field that maps your foreign key.
In the model add below function.
public function setFooBarAttribute($value)
{
$this->attributes['foo_bar'] = $value?:null;
}
In an MS Access datasheet, is it possible to filter those records whose value is null or empty in a specific field in my table?
Yes.
WHERE myCol IS NULL OR LEN(myCol) = 0
In your SQL statement:
WHERE Nz(CompanyName, '') = ''
In your form's filter property:
Nz(CompanyName, '') = ''
The solution posted by Mitch Wheat will also work. I'm not certain which one will offer the best performance. If you are using Mitch's solution and you are also using other conditions in your Where clause, don't forget to insert parenthesis like this:
WHERE (myCol IS NULL OR LEN(myCol) = 0) AND myCol2 = True
Using a function in the criterion means you can't use the indexes. #Mitch Wheat's solution will use the index for the Is Null test, but not for the Len() test.
A sargable WHERE clause would be this:
WHERE myCol Is Null OR myCol = ""
But I'd recommend turning off "allow zero-length strings" and then you need only do the Null test, which on an indexed field will be extremely fast.
For what it's worth, I find it extremely annoying that MS changed the defaults for new text fields to have Allow ZLS turned on. It means that I have to change every one of them when I'm using the table designer to create new fields.