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However, in certain situations, it may be necessary or at least desirable to turn to SQL-specific queries to extract and transform the data you want. Indeed if any form of in-depth customization is on the cards, then this could be crucial to achieving your aims.
Here is a quick introduction to what role SQL has to play in making WordPress work as it does, and a few basic querying tips to get you started.
Understanding the basics
WordPress is based on the open-source MySQL database platform, but with lots of tweaks implemented to make it distinct.
As you might expect, for the most part, the WordPress platform does not expect its users to tinker too much with its database implementation. So if you want to do things like identifying the SQL deadlock victim if multiple processes are battling for server resources, or use other custom queries, a different approach is needed.
Implementing SQL queries within WordPress
In order to access the database and run SQL queries of your own composition, you need to make use of the wpdb extraction class.
Prefixing $wpdb with global will enable you to implement scripts yourself, and have them play out as intended. Take the following snipped as an example:
<?php
function get_some_data(){
global $wpdb;
return $wpdb->get_results(“SELECT * FROM {$wpdb->prefix}some_table WHERE some_column = ‘some value'”);
}
This gives an indication of how implementing SQL queries is achievable, in this case, to find results from within a particular range of values in the tables of your WP site’s database.
When it comes to actually write those queries, it is best to go in-depth and study the best practices and standards for SQL syntax. Be aware that you can hamper performance and create issues if your queries are not well optimized, so don’t rush into adding your own without learning the ropes first.
Considering the security implications & compatibility issues
Another point that beginners must take into account when taking the step of querying the WP database via their own SQL statements is that this can leave you exposed to common types of attack, namely SQL injection.
This is chiefly relevant in the context that the data being queried is user-generated; for example, when people enter information into a form on your website, it could be exploited by malicious third parties as a means of penetrating your site’s security.
The simplest way around this is to use the wpdb::prepare() method. This will shield user-entered data from being able to interfere with the inner workings of your database, like so:
sql = $wpdb->prepare( “SELECT * FROM {$wpdb->prefix}some_table WHERE some_column = %s”, ‘some user submitted string’ );
Again, it pays to go in-depth with your learning and implementation of this precautionary measure, since cutting corners can only lead to larger issues down the line.
Compatibility is another talking point in this context since you will likely be using at least a few plugins in conjunction with your WordPress site. Third-party solutions can be rendered inoperable if the SQL you add is not implemented in line with best practices, so again you cannot afford to stray from the straight and narrow.
Final thoughts
Not everyone will need to directly query their WP database with SQL, but it is nice to know that the option is there alongside other maintenance and modification avenues.
If in doubt, seek expert assistance from an experienced WordPress developer; one who is well versed in SQL above all else.