Question

I have a php array like the one below.

$arr = array(
                array(
                    "date"=>date('Y-m-d'),
                    "message"=>"test message 1",
                    "from_id"=>21,
                    "to_id"=>14
                ),
                array(
                    "date"=>date('Y-m-d'),
                    "message"=>"test message 2",
                    "from_id"=>23,
                    "to_id"=>12
                )               
            );

I do a json_encode on this array to convert it json.

$jsonarr =  json_encode($arr);

Output of $jsonarr:

[
 {"date":"2012-11-22","message":"test message 1","from_id":21,"to_id":14},
 {"date":"2012-11-22","message":"test message 2","from_id":23,"to_id":12}
]

After that i insert this in mysql table. Everything is fine till here.

Now i have to update this with another json by concatenation.

Another JSON:

[
 {"date":"2012-11-22","message":"test message 3","from_id":28,"to_id":2},
 {"date":"2012-11-22","message":"test message 4","from_id":53,"to_id":72}
]

And i want the field in my mysql table to display like this:

[
 {"date":"2012-11-22","message":"test message 1","from_id":21,"to_id":14},
 {"date":"2012-11-22","message":"test message 2","from_id":23,"to_id":12},
 {"date":"2012-11-22","message":"test message 3","from_id":28,"to_id":2},
 {"date":"2012-11-22","message":"test message 4","from_id":53,"to_id":72}
]

How can i write an UPDATE query for this.

I can do this by using 2 queries. One select query then formatting the field and later updating. But can this be achieved with one query ?

Answer 1

The solution to your immediate problem is this:

MySQL does not natively support JSON values. You need to fetch the value from the database:

SELECT FOR UPDATE my_json_field
FROM my_table
WHERE id = 555;

Then modify it in the PHP script:

$my_array = json_decode($value_of_my_json_field);
$my_array = array_merge($my_array, $arr);
$value_of_my_json_field = json_encode($my_array);

Then update it in the DB:

UPDATE my_table
SET my_json_field = :value_of_my_json_field
WHERE id = 555;

Make sure this happens in a transaction. Also, you need to use the InnoDB storage engine.

But the more interesting question is why do you need to store JSON in the DB? Why not use a separate table:

• Table: messages
  • id integer
  • date timestamp
  • from_id integer (this should be a foreign key)
  • to_id integer (this should be a foreign key)

Then you could simply insert into that table. That’s the correct way of doing this. If you don’t have a very good reason to use JSON, I would suggest getting rid of it.