从MYSQL数据库创建JSON字符串

I am trying to get data from MySQL database in form of a json string.

I read this answer: JSON encode MySQL results

But this is limited to a single table. What if I want to get data from multiple tables (name from userDetails, purchase data from UserPurchases etc)? How can I create a custom string, getting data from multiple tables and creating a json string like it’s from a single table only?

 $query = "SELECT * FROM `thing` WHERE `id` = :thingId";
    $stmt = $dbh->prepare ( $query );
    $stmt->bindParam ( ":thingId" , $_GET['thingId']  );
    $stmt->execute ( );
    $rslt  =  $stmt->fetch ( );
    $thingName  = $rslt['name'];
    $thingOwnerId = $rslt['userId'];
    $thingDescription = $rslt['thingDescription'];

// Getting the thing owner details
    $query = "SELECT * from `user` WHERE ( `id` = :id ) ";    
    $stmt = $dbh->prepare( $query );
    $stmt->bindParam ( ":id" , $thingOwnerId );
    $stmt->execute(  );
    $rslt = $stmt->fetch ( );
    $thingOwnerName = $rslt['firstName']." ".$rslt['lastName'];

Now, how to make a single json strong out of this data from separate tables. The string should have the thingName,thingOwnerId, thingDescription, thingOwnerName.

Collect the required data from your queries in an array, then output that array in a JSON encoded format to the browser. Remember to set the Content-Type: application/json header before any output.

PHP

//collect your data in an array
$data=array(
    'name'=>$thingOwnerName,
    'description'=>$thingDescription,
    'otherField'=>$someValue
    ...
);

//send JSON header to browser
header('Content-Type: application/json');

//echo JSON encoded data
echo json_encode($data);

If they are different queries, you can merge the results and encode that array like this:

$merged = array();

 $query = "SELECT * FROM `thing` WHERE `id` = :thingId";
    $stmt = $dbh->prepare ( $query );
    $stmt->bindParam ( ":thingId" , $_GET['thingId']  );
    $stmt->execute ( );
    $rslt  =  $stmt->fetch ( );
$merged['thing'] = $rslt;    

// Getting the thing owner details
    $query = "SELECT * from `user` WHERE ( `id` = :id ) ";    
    $stmt = $dbh->prepare( $query );
    $stmt->bindParam ( ":id" , $thingOwnerId );
    $stmt->execute(  );
    $rslt = $stmt->fetch ( );
$merged['user'] = $rslt;

echo json_encode($merged);

you can also create a class in PHP, set database values to this class and encode to JSON, eg.:

<?php

class MyCustomJson
{
    public $userId;
    public $thingId;
    //and go on...
}

//set db values to this class
$myCustomJson = new MyCustomJson();
//..read data from User table and set table values to your custom object
$myCustomJson->userId = $row["id"];
//..read data from Thing table and set table values to your custom object
$myCustomJson->thingId = $row["id"];

//and encode your custom object to json
echo json_encode($myCustomJson);
?>