Conditional row count across 4 tables

Question

I have the following function that works fine. Is there a better way to do it and will this be efficient if I have 100+ rows returned from each table?

The database

Tables

• wcx_articles
• wcx_videos
• wcx_apps
• wcx_links

The corresponding _active column for each table

• article_active
• video_active
• app_active
• link_active

_active is a switch 1 or 0

This is my current function

public function findInactiveItems() {

    $query = "SELECT * FROM wcx_articles WHERE article_active = '0'
    UNION
    SELECT * FROM wcx_videos WHERE video_active = '0'
    UNION
    SELECT * FROM wcx_apps WHERE app_active = '0'
    UNION
    SELECT * FROM wcx_links WHERE link_active = '0'
    ";
        if( $this->num_rows( $query ) > 0 ) {    
            $count = $this->num_rows($query);
            return $count;
        }
    }

 public function num_rows( $query ) {
    $query = $this->link->query( $query );
    if( mysqli_error( $this->link ) ) {
        $this->log_db_errors( mysqli_error( $this->link ), $query, 'Fatal' );
        return mysqli_error( $this->link );
    }
    else {
        return mysqli_num_rows( $query );
    }
    mysqli_free_result( $query );
}

Answer 1

SQL

If you want a count, ask for a count. Don't ask the server to send all the data for all the rows, just to have the client count the rows. (A few hundred rows is a trivial amount of data for a database to handle, but still, you should follow good practices.)

SELECT SUM(inactive_count) AS inactive_count
    FROM (
        SELECT COUNT(article_active) AS inactive_count
            FROM wcx_articles WHERE article_active = '0'
        UNION ALL
        SELECT COUNT(video_active)
            FROM wcx_videos WHERE video_active = '0'
        UNION ALL
        SELECT COUNT(app_active)
            FROM wcx_apps WHERE app_active = '0'
        UNION ALL
        SELECT COUNT(link_active)
            FROM wcx_links WHERE link_active = '0'
    ) AS wcs_objects;

Schema

If in fact all four of your tables are union-compatible with each other, then you should strongly consider merging them into one table with a wcx_type attribute that declares what type of object that row represents.

Are your …_active columns really strings? Those columns should be of the BOOLEAN (i.e., TINYINT(1)) type. The query should be adjusted accordingly: use …_active = 0 instead of …_active = '0'.

PHP

You reused the $query parameter to store the result of the query. Don't be stingy like that — it's confusing. Use a new variable to store the result.

You have a leak: mysqli_free_result( $query ); never gets called, because that statement is unreachable.

You are mixing the object-oriented and procedural styles of mysqli. You should either use the object-oriented style consistently…

public function num_rows($query) {
    if (!($result = $this->link->query($query))) {
        $this->log_db_errors($this->link->error, $result, 'Fatal');
        return $this->link->error;
    }
    $num_rows = $result->num_rows;
    $result->free();
    return $num_rows;
}

or use the procedural style consistently…

public function num_rows($query) {
    if (!($result = mysqli_query($this->link, $query))) {
        $this->log_db_errors(mysqli_error($this->link), $result, 'Fatal');
        return mysqli_error($this->link);
    }
    $num_rows = mysqli_num_rows($result);
    mysqli_free_result($result);
    return $num_rows;
}