External – WP Query Function (Custom Query)

WP_Query adds two important functionalities within WordPress –

• You can use WP_Query to detect the type of request that WordPress is currently handling.
• You can use the various functions offered by WP_Query to perform common tasks inside loops.

tax_query:

• Tax_query is a parameter in WP_Query which is used to query taxonomies.
• It can be used to query multiple taxonomies by using the relation operator in the parameters.

meta_query:

• meta_query is a parameter in WP_Query which is used to query multiple metadatas.
• It can be used to query meta values by using the relation operator in the parameters.

For more information, you can have a look at the below resources –

• Class Reference/WP_Query
  • See especially Multiple Loops and Meta Queries.
• You Don’t Know WP_Query – Andrew Nacin
  • See Slides, especially 33 through 36 — WP_Query() by default queries & caches metadata and terms.
  • See pre_get_posts hook.
• WP_Query Arguments Guide
• Make Sense of WP_Query
• Performance Improvement (WP.com VIP)
  • Database Queries
  • Meta Queries