How to use a different database to list and manage comments in the backend

You can filter query. See wpdb::query() in wp-includes/wp-db.php.

You get the complete SQL string as parameter. Then look for queries to the comments table:

add_filter( 'query', function( $query ) 
{
    global $wpdb;

    if ( FALSE === stripos( $query, "FROM $wpdb->comments" )
        return $query;

    // Now change the SQL
});

But you have to catch all the JOINs with other tables too. Not sure if this is possible in an elegant way.

Related Posts:

  1. Using wpdb to connect to a separate database
  2. WPDB Insert or if exists Update
  3. get_results using wpdb
  4. $wpdb won’t insert NULL into table column
  5. Get error messages when $wpdb->insert() returns false?
  6. Does dbDelta delete columns as well?
  7. How to fetch Data in WordPress using MySQLi or $wpdb
  8. wpdb->insert multiple record at once
  9. How to define composite keys with dbDelta()
  10. Does wpdb add considerable overhead on queries with large result sets?
  11. Why does $wpdb return strings for mysql integer values?
  12. $wpdb->prepare() warning in WordPress 3.5
  13. Inserting data into custom tables
  14. Hook into $wpdb
  15. Display data from a non wordpress database on a page template
  16. How does $wpdb handle COUNT(*)
  17. WordPress database error: [Query was empty] [closed]
  18. Inserting Post Meta From SQL
  19. Connecting to external oracle database
  20. Can’t save ajax value to database
  21. $wpdb variable throw this error Call to a member function get_results() on a non-object in
  22. Updating all rows of table with $wpdb
  23. How to execute mulitple statement SQL queries using $wpdb->query?
  24. Is $wpdb->prepare escaping to much? How to use it properly?
  25. When and why should I use $wpdb different return types?
  26. How wordpress accesses its own database
  27. Remove database entries where post_date > expiration date
  28. Error connecting to DB in /wp-includes/wp-db.php on line 1538 [closed]
  29. How to query the WordPress database to get posts of a certain custom post type, taxonomy and field?
  30. Getting all the users who have author privilege
  31. Multiple postmeta with same name for one post in wp_postmeta table
  32. WP Database Table to CSV file
  33. wpdb_prepare with multiple or condition
  34. Show last modified date of database
  35. $wpdb->insert is not working
  36. Extracting the post_id via the wp_insert_post action (external db query)
  37. In what part of the WordPress core does the users table and usermeta table get joined?
  38. Advanced SELECT query with condtional statements
  39. WordPress choose wrong database
  40. Redirecting to old domain after migration website
  41. Retrieve data from the database to table such as comments in the admin control panel
  42. Create table from array with prepare
  43. Update from 4.5 to 4.6 failing
  44. Does WordPress $wpdb functions wait when table is locked?
  45. $wpdb->insert Giving duplicates
  46. I’m not able to get access to $wpdb [duplicate]
  47. $wpdb error (Call to a member function insert() on a non-object)
  48. Have working sql query… trying to adjust it to use $wpdb
  49. Problem in using wpdb
  50. $wpdb->query can’t insert data
  51. How to fetch records from database WordPress
  52. Best practice to import user base (subscribers) from one website to another?
  53. AJAX wp-mysql running too slow
  54. How to delete post comments from the database via SQL statement?
  55. Problem migrating to localhost
  56. Clear Terms from Taxonomy for Specific Post IDs?
  57. Connecting to a different database
  58. Query Column of Specific ID from Database Table
  59. How to delete a particular row in a database table
  60. How to create more than one new wpdb object?
  61. Update multiple rows in one query
  62. SELECT SQL_CALC_FOUND_ROWS with wordpress search
  63. How to connect and insert data in database of wordpress?
  64. Should I use an additional column in the DB?
  65. access JSON results from wordpress database with wpdb
  66. Getting value from database table depending on field value
  67. add_post_meta — not working
  68. Select From wpdb – Author/User Directory page
  69. wpdb->insert not inserting first variable
  70. How do I have a user upload a blog post and then retrieve that to display in a card on the site?
  71. How to escape percentage sign(%) in sql query with $wpdb->prepare?
  72. wpdb Insert unknown post data dynamic foreach loop
  73. How do I get database rows from a custom table using wpdb?
  74. Insert NULL value using prepare()
  75. Help with $wpdb on custom code
  76. “BS_” rows in postmeta table
  77. $wpdb->insert duplicating rows
  78. How to rerieve comments and their replies from DB
  79. Help posting values to DB on submit using $wpdb->query
  80. How to add download link from database on custom page template?
  81. 2 $wpdb queries causing error Table ‘wp_postmeta’ is specified twice, both as a target for ‘UPDATE’
  82. insert data from a form:: Warning Empty query mysqli::query()
  83. How can I get $wpdb to show MySQL warnings?
  84. About wp database hooks (error establishing connection)
  85. How to get specific table by current user login
  86. Using $wpdb to insert data into a table
  87. How To connect to the same WordPress database with different database user
  88. Accessing content from third party as native posts in WordPress
  89. Should I Use only wpdb Class to Write Custom Queries?
  90. Call to a member function insert()
  91. I have include wp-config, should I add global $wpdb also?
  92. Can’t Install WordPress (local) Failed to open file wp-includes/wp-db.php
  93. using same mysql user with many databases
  94. Pulling values from a sepcific row in table
  95. Creating Tables in WordPress Database
  96. Inserting into data into external DB using WPDB
  97. Insert Extra fields added in the front end registration form to DB
  98. $wpdb->insert not working for last select option
  99. $wpdb->prepare returns empty array
  100. Uploading to WordPress Database
error code: 523