$wpdb doesn’t appear to work on page inside of a plugin

The $wpdb object is part of WordPress, so wouldn’t be loaded into a standalone PHP page as it is into a WordPress template.

You might want to look into creating your own page templates, then you could run your database query as part of that page template.

As a side note: You are currently trusting input from the user ($_REQUEST) which is a Bad Thing™, as it could make you vulnerable to SQL Injection attacks. The code example you give could be adapted as below to be less vulnerable:

global $wpdb;
$orderby = $_REQUEST['orderby'];
// Limit the values of orderby to ones we know to be safe
$acceptable_orderbys = array( 'name', 'age', 'height' );
if ( in_array( $orderby, $acceptable_orderbys ) )
    $clean_orderby = $orderby;
else
    $clean_orderby = 'name';
$sql = "SELECT * FROM wp_nc_location ORDER BY $clean_orderby";
$data = $wpdb->get_results($sql);

I’ve not tested the above code, but the key thing is to check the value of $orderby is known to be safe before you put it into the DB query.

Related Posts:

  1. Differences between wpdb->get_results() and wpdb->query()
  2. How to Use Wildcards in $wpdb Queries Using $wpdb->get_results & $wpdb->prepare?
  3. wpdb get posts by taxonomy SQL
  4. Multipart/formatted MySQL query problem
  5. Custom $wpdb Query for Custom Post Type by Category
  6. Can’t pass table to $wpdb->prepare
  7. $wpdb->get_var not returning a result
  8. Most effective use of DB querys
  9. $wpdb->query() vs. $wpdb->get_results() vs. phpMyAdmin
  10. wpdb::prepare() isn’t working
  11. Strange string in console from wpdb query
  12. Using $wpdb->update but confused on the WHERE in and SET
  13. What’s wrong with my $wpdb prepare?
  14. Make one query for adding entries to database
  15. How to execute a SQL-query which contains multiple queries using $wpdb->query?
  16. Alter a specific query on WordPress
  17. wpdb->term_taxonomy count posts from both published and private posts?
  18. wpdb print all post meta
  19. Plugin will sort users by usermeta
  20. wpdb query problem to access previous 3 days posts
  21. How to write: $wpdb->update having WHERE NOT value pair in the array
  22. I can’t figure out what’s wrong with this statement. $wpdb->query update
  23. Use mysql_query instead of $wpdb query
  24. wpdb COALESCE won’t work
  25. Custom Query – Based on user input
  26. Custom SQL Query passing array to WHERE p.id
  27. Get posts from category with custom query
  28. Custom Query returns array, but I can’t see it’s elements
  29. Valid SQL query return empty
  30. mysql query – how to escape apostrophe?
  31. $wpdb->prepare affecting the query?
  32. prepare function sql safe method
  33. Updating with $qpdb->query() always returns 0 rows affected
  34. How to return count of custom post type posts with a specific custom field value via $wpdb?
  35. WordPress Mysql query and Duplicate
  36. How do I query for posts by custom meta and those that have been stickied?
  37. Help with Related Posts Function
  38. wpdb update multiple row?
  39. Formatting a date/time returned from a custom $wpdb query
  40. Improve performance of slow query
  41. How do I get specific readable results from this query and array results
  42. implementing my wp_query using $wpdb class
  43. Exclude Posts from a Widget
  44. Fastest and most efficient SQL query to check if UID exists
  45. Use $wpdb->get_results with filter based on array
  46. $wpdb query for price in custom field value
  47. Display result from custom post meta query
  48. Wpdb empty result only if language is Russian
  49. Run an update query in a function
  50. How to fix this insert? Don’t work for me!
  51. Problem on wpdb queries, wp_insert_post, wp_insert_user etc. The query runs twice
  52. Update vs Insert logic but the last key is always inserted?
  53. There is way to improve this query? wordpress get post data and some meta data
  54. $wpdb: how to use a query as a base for another query?
  55. Wpdb generates too many queries
  56. Custom Query for searching through custom fields
  57. Mysql query and odd results
  58. How to reference same column name but different table in custom db query
  59. Retrieving custom field array value through db query
  60. How to get one result using wpdb class?
  61. Delete query won’t run
  62. update $wpdb one query
  63. wp_dropdown_categories with multiple select
  64. How to tune search argument in WP_Query to show only exactly the same results?
  65. How to get my loop to pull posts into three columns
  66. Date query year and month OR just year
  67. Are database queries created using WordPress filters protected from SQL injection?
  68. get post id using the $query_vars variable
  69. How to query the WordPress database to get posts of a certain custom post type, taxonomy and field?
  70. Huge amount of queries on my site
  71. How do I use get_query_var() within plguin code
  72. How to display related posts by same publish date?
  73. Get post according to current taxonomy
  74. Alter query with posts_clauses to retrieve NULL values last
  75. Query based on title, with ‘compare’ => ‘IN’
  76. Sorting main query by custom taxonomy slug
  77. Query posts according to specific post meta values
  78. empty query breaks other queries
  79. Problem in exploding the_content to array
  80. $wpdb->query can’t insert data
  81. how to insert missing tags into the posts through mySQL?
  82. How to write update query in WordPress to expire transients
  83. Query Nickname rather than Display Name in custom Woocommerce plugin
  84. Get previous posts list
  85. how to replace old DW site with new WP site? [closed]
  86. WordPress SQL query to tag all posts containing a specific word on title
  87. How to rearrange a pool of posts joined using two queries?
  88. Disable (or limit) queries when certain content (or data) is not needed (or showed)
  89. Custom query Custom-Post-Types creates error
  90. Doing $wpdb->get_results returns NULL, doing the same query in my DB returns correct value
  91. Displaying data from custom table
  92. OR condition not working
  93. Should I Use only wpdb Class to Write Custom Queries?
  94. Add Hook for clearing transient when post is added
  95. Show links to child pages on both parent AND child pages
  96. Modify Global Posts Plugin
  97. SQL Query : how copy all tags of post into their post content in wordpress by sql query
  98. How do I troubleshoot Maximum execution time of 60 seconds exceeded in updating a Media File?
  99. Admin Post List table Query filtering “WHERE” for custom post type
  100. How to use a dynamic term id for the query block
techhipbettruvabetnorabahisbahis forumutaraftarium24eduseduedusedueduedusedusedueduedu