double output from mysql in php - php

Question

I am selecting the tables names from an opencart install.
trying to output the result(single column) as a string formated like a JSON array.
here is the code:
<?php
function getTableNames()
{
//Change these variables depending on the server it will be used on
$server = 'localhost';
$user = 'User1';
$pass = 'pass';
$DBName = 'OpenCartTest';
//returns a single column of all tables in a mysql database named "OpenCartTest"
$tablesGetSQL = 'Select `table_name` from `information_schema`.`TABLES` where `table_schema` like "OpenCartTest" AND `table_name LIKE "oc_customer%"';
$conn = new mysqli($server, $user, $pass, $DBName);
$JSONStringArray = '[';
if(mysqli_connect_errno())
{
echo '---unauthorized---';
}
else
{
$result = $conn->query($tablesGetSQL);
$l = $result->num_rows;
if($l > 0)
{
//for($i = 0;$i < $l;$i++)
while($row = $result->fetch_assoc())
{
//$row = $result->fetch_assoc();
foreach($row as $item)
{
//echo $item . "|";
$JSONStringArray .= "'" . $item . "',";
}
}
}
$JSONStringArray .= substr($JSONStringArray, 0, -1) . ']';
$conn->close();
return $JSONStringArray;
}
}
$output = getTableNames();
echo substr_count($output, "[") . '<br>';
echo $output;
?>
The output is doubled for some reason, there are 2 '[', yet I only set it once to the string. There is also no closing ']' on the first line.
output:
2
['oc_address','oc_affiliate','oc_affiliate_activity','oc_affiliate_login','oc_affiliate_transaction','oc_api','oc_attribute','oc_attribute_description','oc_attribute_group','oc_attribute_group_description','oc_banner','oc_banner_image','oc_banner_image_description','oc_category','oc_category_description','oc_category_filter','oc_category_path','oc_category_to_layout','oc_category_to_store','oc_country','oc_coupon','oc_coupon_category','oc_coupon_history','oc_coupon_product','oc_currency','oc_custom_field','oc_custom_field_customer_group','oc_custom_field_description','oc_custom_field_value','oc_custom_field_value_description','oc_customer','oc_customer_activity','oc_customer_ban_ip','oc_customer_group','oc_customer_group_description','oc_customer_history','oc_customer_ip','oc_customer_login','oc_customer_online','oc_customer_reward','oc_customer_transaction','oc_download','oc_download_description','oc_event','oc_extension','oc_filter','oc_filter_description','oc_filter_group','oc_filter_group_description','oc_geo_zone','oc_information','oc_information_description','oc_information_to_layout','oc_information_to_store','oc_language','oc_layout','oc_layout_module','oc_layout_route','oc_length_class','oc_length_class_description','oc_location','oc_manufacturer','oc_manufacturer_to_store','oc_marketing','oc_modification','oc_module','oc_option','oc_option_description','oc_option_value','oc_option_value_description','oc_order','oc_order_custom_field','oc_order_fraud','oc_order_history','oc_order_option','oc_order_product','oc_order_recurring','oc_order_recurring_transaction','oc_order_status','oc_order_total','oc_order_voucher','oc_osapi_last_modified','oc_product','oc_product_attribute','oc_product_description','oc_product_discount','oc_product_filter','oc_product_image','oc_product_option','oc_product_option_value','oc_product_recurring','oc_product_related','oc_product_reward','oc_product_special','oc_product_to_category','oc_product_to_download','oc_product_to_layout','oc_product_to_store','oc_recurring','oc_recurring_description','oc_return','oc_return_action','oc_return_history','oc_return_reason','oc_return_status','oc_review','oc_setting','oc_stock_status','oc_store','oc_tax_class','oc_tax_rate','oc_tax_rate_to_customer_group','oc_tax_rule','oc_tg_tglite_revolution_slider','oc_upload','oc_url_alias','oc_user','oc_user_group','oc_voucher','oc_voucher_history','oc_voucher_theme','oc_voucher_theme_description','oc_weight_class','oc_weight_class_description','oc_zone','oc_zone_to_geo_zone',
['oc_address','oc_affiliate','oc_affiliate_activity','oc_affiliate_login','oc_affiliate_transaction','oc_api','oc_attribute','oc_attribute_description','oc_attribute_group','oc_attribute_group_description','oc_banner','oc_banner_image','oc_banner_image_description','oc_category','oc_category_description','oc_category_filter','oc_category_path','oc_category_to_layout','oc_category_to_store','oc_country','oc_coupon','oc_coupon_category','oc_coupon_history','oc_coupon_product','oc_currency','oc_custom_field','oc_custom_field_customer_group','oc_custom_field_description','oc_custom_field_value','oc_custom_field_value_description','oc_customer','oc_customer_activity','oc_customer_ban_ip','oc_customer_group','oc_customer_group_description','oc_customer_history','oc_customer_ip','oc_customer_login','oc_customer_online','oc_customer_reward','oc_customer_transaction','oc_download','oc_download_description','oc_event','oc_extension','oc_filter','oc_filter_description','oc_filter_group','oc_filter_group_description','oc_geo_zone','oc_information','oc_information_description','oc_information_to_layout','oc_information_to_store','oc_language','oc_layout','oc_layout_module','oc_layout_route','oc_length_class','oc_length_class_description','oc_location','oc_manufacturer','oc_manufacturer_to_store','oc_marketing','oc_modification','oc_module','oc_option','oc_option_description','oc_option_value','oc_option_value_description','oc_order','oc_order_custom_field','oc_order_fraud','oc_order_history','oc_order_option','oc_order_product','oc_order_recurring','oc_order_recurring_transaction','oc_order_status','oc_order_total','oc_order_voucher','oc_osapi_last_modified','oc_product','oc_product_attribute','oc_product_description','oc_product_discount','oc_product_filter','oc_product_image','oc_product_option','oc_product_option_value','oc_product_recurring','oc_product_related','oc_product_reward','oc_product_special','oc_product_to_category','oc_product_to_download','oc_product_to_layout','oc_product_to_store','oc_recurring','oc_recurring_description','oc_return','oc_return_action','oc_return_history','oc_return_reason','oc_return_status','oc_review','oc_setting','oc_stock_status','oc_store','oc_tax_class','oc_tax_rate','oc_tax_rate_to_customer_group','oc_tax_rule','oc_tg_tglite_revolution_slider','oc_upload','oc_url_alias','oc_user','oc_user_group','oc_voucher','oc_voucher_history','oc_voucher_theme','oc_voucher_theme_description','oc_weight_class','oc_weight_class_description','oc_zone','oc_zone_to_geo_zone']
I cannot spot where I've gone wrong. Maybe I Will try it on a diferent server next.

Answer 1

Don't create your JSON string manually, just use json_encode, thats why this function exists anyway:
First is gather all the table names inside a container first, finish the gathering, the loop and the whole bit, after your done with that, then encode it.
$result = $conn->query($tablesGetSQL);
$JSONStringArray = array(); // initialize container
while($row = $result->fetch_assoc()) {
$JSONStringArray[] = $row['table_name']; // push all table names
}
// finally, encode
$JSONStringArray = json_encode($JSONStringArray);
$conn->close();
return $JSONStringArray;

Answer 2

You are getting two copies because of this line
$JSONStringArray .= substr($JSONStringArray, 0, -1) . ']';
You do the .= which is doing the substr, and adding it to the original, you should just do an =
ie, should just be:
$JSONStringArray = substr($JSONStringArray, 0, -1) . ']';
As a side note, there's no need to build a JSON string, PHP has a built in method to generate the json string. Instead you can do
$data = array();
while($row = $result->fetch_row())
{
$data += $row; // append returned array to the data array, since you wanted it future proof incase you added more columns to the SELECT query
}
// close connection
return json_encode($data);