1. Parsing Strange:
URL to SQL to HTML
Hal Stern
snowmanonfire.com headshot by Richard Stevens
http://dieselsweeties.com
slideshare.net/freeholdhal
© 2010 Hal Stern
Some Rights Reserved

2. Why Do You Care?
• Database performance = user experience
• A little database expertise goes a long way
• Taxonomies for more than sidebar lists
• Custom post types (!!)
• WordPress is a powerful CMS
> Change default behaviors
> Defy the common wisdom
> Integrate other content sources/filters
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 2

3. Flow of Control
• Web server URL manipulation
> Real file or permalink URL?
• URL to query variables
> What to display? Tag? Post? Category?
• Query variables to SQL generation
> How exactly to get that content?
• Template file selection
> How will content be displayed?
• Content manipulation
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 3

4. Whose File Is This?
• User URL request passed to web server
• Web server checks
.htaccess file <IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /whereyouputWordPress/
> WP install root RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
> Other .htaccess RewriteRule
</IfModule>
. /index.php [L]
files may interfere
• Basic rewriting rules:
If file or directory URL doesn’t exist, start
WordPress via index.php
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 4

5. Example Meta Fail: 404 Not Found
myblog/
myblog/wp-content (etc)
myblog/images
• Access broken image URLs for
unintended results: no 404 pages!
myblog/images/not-a-pic.jpg!
• Web server can’t find file, assumes it’s a
permalink, hands to WP
• WP can’t interpret it, so defaults to home
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 5

6. What Happens Before The Loop
• Parse URL into a query
• Set conditionals & select templates
• Execute the query & cache results
• Run the Loop:
<?php
if (have_posts()) :
while (have_posts()) :
the_post();
//loop content
endwhile;
endif;
?>
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 6

7. Examining the Query String
<?php
global $wp_query;
echo ”SQL for this page ";
echo $wp_query->request;
echo "<br>";
?>
• SQL passed to MySQL in WP_Query
object’s request element
• Brute force: edit theme footer.php
to
see main loop’s query for displayed page
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 7

8. “Home Page” Query Deconstruction
SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1
AND wp_posts.post_type = 'post’ AND
(wp_posts.post_status = 'publish' OR
wp_posts.post_status = 'private’)
ORDER BY wp_posts.post_date DESC LIMIT 0, 10
Get all fields from posts table, but limit number of returned rows
Only get posts, and those that are published or private to the user
Sort the results by date in descending order
Start results starting with record 0 and up to 10 more results
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 8

9. Query Parsing
• parse_request() method of WP_Query
extracts query variables from URL
• Execute rewrite rules
> Pick off ?p=67 style http GET variables
> Match permalink structure
> Match keywords like “author” and “tag”
> Match custom post type slugs
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 9

10. Query Variables to SQL
• Query type: post by title, posts by category
or tag, posts by date
• Variables for the query
> Slug values for category/tags
> Month/day numbers
> Explicit variable values
?p=67 for post_id
• post_type variable has been around for
a while; CPT fill in new values
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 10

11. Simple Title Slug Parsing
/2010/premio-sausage
SELECT wp_posts.* FROM wp_posts WHERE 1=1 AND YEAR
(wp_posts.post_date)='2010' AND wp_posts.post_name = 'premio-
sausage' AND wp_posts.post_type = 'post' ORDER BY
wp_posts.post_date DESC
• Rewrite matches root of permalink,
extracts tail of URL as a title slug
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 11

12. Graphs and JOIN Operations
• WordPress treats tags and categories as
“terms”, mapped 1:N to posts
• Relational databases aren’t ideal for this
> INNER JOIN builds intermediate tables on
common key values
• Following link in a social graph is
equivalent to an INNER JOIN on tables of
linked items
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 12

13. WordPress Taxonomy Tables
wp_posts wp_term_relationships wp_term_taxonomy
post_id object_id term_taxonomy_id
…. term_taxonomy_id term_id
post_date taxonomy
… description
post_content
• Term relationships table maps
N:1 terms to each post wp_terms
term_id
• Term taxonomy maps slugs name
1:N to taxonomies slug
• Term table has slugs for URL
mapping
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 13

14. Taxonomy Lookup
/tag/premio
SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts
INNER JOIN wp_term_relationships ON
(wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_term_taxonomy ON
(wp_term_relationships.term_taxonomy_id =
wp_term_taxonomy.term_taxonomy_id)
INNER JOIN wp_terms ON
(wp_term_taxonomy.term_id = wp_terms.term_id)
WHERE 1=1 AND wp_term_taxonomy.taxonomy = 'post_tag' AND wp_terms.slug IN
('premio') AND wp_posts.post_type = 'post' AND (wp_posts.post_status =
'publish' OR wp_posts.post_status = 'private') GROUP BY wp_posts.ID ORDER
BY wp_posts.post_date DESC LIMIT 0, 10
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 14

15. More on Canonical URLs
• Canonical URLs improve SEO
• WordPress is really good about generating
301 Redirects for non-standard URLs
• Example: URL doesn’t appear to match a
permalink, WordPress does prediction
> Use “LIKE title%” in WHERE clause
> Matches “title” as initial substring with %
wildcard
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 15

16. Modifying the Query
• Brute force isn’t necessarily good
> Using query_posts() ignores all previous
parsing, runs a new SQL query
• Filter query_vars
> Change default parsing (convert any day to a
week’s worth of posts, for example)
• Actions parse_query & parse_request
> Access WP_Query object before execution
> is_xx() conditionals are already set
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 16

17. SQL Generation Filters
• posts_where
> More explicit control over query variable to
SQL grammar mapping
• posts_join
> Add or modify JOINS for other graph like
relationships
• Many other filters
> Change grouping of results
> Change ordering of results
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 17

18. Custom Post Types
• Change SQL WHERE clause on post type
> wp_posts.post_type=‘ebay’
• Add new rewrite rules for URL parsing similar
to category & tag
> Set slug in CPT registration array
'rewrite' => array ("slug" => “ebay”),
• Watch out for competing, overwritten or
unflushed rewrite entries
<?php echo "<pre>”;
print_r(get_option('rewrite_rules'));
echo "</pre>”;
?>
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 18

19. Applications
• Stylized listings
> Category sorted alphabetically
> Use posts as listings of resources (jobs,
clients, events) – good CPT application
• Custom URL slugs
> Add rewrite rules to match slug and set query
variables
• Joining other social graphs
> Suggested/related content
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 19

20. Template File Selection
• is_x() conditionals set in query parsing
• Used to drive template selection
> is_tag() looks for tag-slug, tag-id, then tag
> Full search hierarchy in Codex
• template_redirect action
> Called in the template loader
> Add actions to override defaults
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 20

21. HTML Generation
• Done in the_post() method
• Raw content retrieved from MySQL
> Short codes interpreted
> CSS applied
• Some caching plugins generate and store
HTML, so YMMV
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 21

22. Why Do You Care?
• User experience improvement
> JOINS are expensive
> Large table, repetitive SELECTs = slow
> Running query once keeps cache warm
> Category, permalink, title slug choices matter
• More CMS, less “blog”
> Alphabetical sort
> Adding taxonomy/social graph elements
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 22

23. Resources
• Core files where SQL stuff happens
> query.php
> post.php
> canonical.php
> rewrite.php
• Template
loader
search
path
> http://codex.wordpress.org/Template_Hierarchy
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 23

24. Contact
Hal Stern
freeholdhal@gmail.com
@freeholdhal
snowmanonfire.com
facebook.com/hal.stern
slideshare.net/freeholdhal
© 2010 Hal Stern
Some Rights Reserved WordCamp Boulder 24