The $wpdb object is based on ezSQL, it does not add much overhead, so I would not worry about that. Opening a second connection to the database yourself will probably lead to more overhead than using the $wpdb functions.
The three queries you have described are ideal queries to do in the database (a small result set from a large dataset), so you should not emulate them in PHP. Be sure to add some indexes to the table to speed the queries up (one on city at least). Use the EXPLAIN feature of MySQL to know what the database is doing to execute your query and how you can help it.
Related Posts:
- Differences between wpdb->get_results() and wpdb->query()
- How to Use Wildcards in $wpdb Queries Using $wpdb->get_results & $wpdb->prepare?
- wpdb get posts by taxonomy SQL
- Multipart/formatted MySQL query problem
- Custom $wpdb Query for Custom Post Type by Category
- Can’t pass table to $wpdb->prepare
- $wpdb->get_var not returning a result
- $wpdb->query() vs. $wpdb->get_results() vs. phpMyAdmin
- wpdb::prepare() isn’t working
- $wpdb doesn’t appear to work on page inside of a plugin
- Strange string in console from wpdb query
- Using $wpdb->update but confused on the WHERE in and SET
- What’s wrong with my $wpdb prepare?
- Make one query for adding entries to database
- How to execute a SQL-query which contains multiple queries using $wpdb->query?
- Alter a specific query on WordPress
- wpdb->term_taxonomy count posts from both published and private posts?
- wpdb print all post meta
- Plugin will sort users by usermeta
- wpdb query problem to access previous 3 days posts
- How to write: $wpdb->update having WHERE NOT value pair in the array
- I can’t figure out what’s wrong with this statement. $wpdb->query update
- Use mysql_query instead of $wpdb query
- wpdb COALESCE won’t work
- Custom Query – Based on user input
- Custom SQL Query passing array to WHERE p.id
- Get posts from category with custom query
- Custom Query returns array, but I can’t see it’s elements
- Valid SQL query return empty
- mysql query – how to escape apostrophe?
- $wpdb->prepare affecting the query?
- prepare function sql safe method
- Updating with $qpdb->query() always returns 0 rows affected
- How to return count of custom post type posts with a specific custom field value via $wpdb?
- WordPress Mysql query and Duplicate
- How do I query for posts by custom meta and those that have been stickied?
- Help with Related Posts Function
- wpdb update multiple row?
- Formatting a date/time returned from a custom $wpdb query
- Improve performance of slow query
- How do I get specific readable results from this query and array results
- implementing my wp_query using $wpdb class
- Exclude Posts from a Widget
- Fastest and most efficient SQL query to check if UID exists
- Use $wpdb->get_results with filter based on array
- $wpdb query for price in custom field value
- Display result from custom post meta query
- Wpdb empty result only if language is Russian
- Run an update query in a function
- How to fix this insert? Don’t work for me!
- Problem on wpdb queries, wp_insert_post, wp_insert_user etc. The query runs twice
- Update vs Insert logic but the last key is always inserted?
- There is way to improve this query? wordpress get post data and some meta data
- $wpdb: how to use a query as a base for another query?
- Wpdb generates too many queries
- Custom Query for searching through custom fields
- Mysql query and odd results
- How to reference same column name but different table in custom db query
- Retrieving custom field array value through db query
- How to get one result using wpdb class?
- Delete query won’t run
- update $wpdb one query
- get_results using wpdb
- Add multiple value to a query variable in WordPress
- wp_dropdown_categories with multiple select
- How to get my loop to pull posts into three columns
- Date query year and month OR just year
- Are database queries created using WordPress filters protected from SQL injection?
- Remove Unnecessary Mysql Query
- Grouping related postmeta data via SQL query
- How To Get Some Data From WordPress Database Using WordPress $wpdb Query?
- Huge amount of queries on my site
- Using pre_get_posts to target a query in the sidebar
- How do I use get_query_var() within plguin code
- How to display related posts by same publish date?
- Get post according to current taxonomy
- Ordering by a metadata subfield in WordPress?
- Alter query with posts_clauses to retrieve NULL values last
- Issue with using add_rewrite_rule() for post querying custom fields
- Sorting main query by custom taxonomy slug
- Query posts according to specific post meta values
- $wpdb->query can’t insert data
- What is wrong with my wp query, cant exclude the category that i want
- how to insert missing tags into the posts through mySQL?
- How to write update query in WordPress to expire transients
- Query Nickname rather than Display Name in custom Woocommerce plugin
- Get previous posts list
- how to replace old DW site with new WP site? [closed]
- WordPress SQL query to tag all posts containing a specific word on title
- Order terms by count – missing terms
- Querying Advanced Custom Fields
- Disable (or limit) queries when certain content (or data) is not needed (or showed)
- Can I include get_posts in this array?
- Rewrite rule for query params
- Doing $wpdb->get_results returns NULL, doing the same query in my DB returns correct value
- Displaying data from custom table
- SEO friendly query vars
- Should I Use only wpdb Class to Write Custom Queries?
- Show links to child pages on both parent AND child pages
- How to figure out correct wp_options to have autoload=’yes’