Add 'execute' method for prepared queries

lib/mysqldb.js

@@ -38,6 +38,29 @@ class MysqlDb {
         return [ rows, fields ];
     }
 
+    /**
+     * Prepare & execute a query.
+     *
+     * @param   {string} sql - The SQL command to be executed.
+     * @param   {Array}  values - Values to be substituted in SQL placeholders.
+     * @returns Array containing array of result rows and array of fields.
+     *
+     * @example
+     *   const [ books ] = await Db.execute('Select * From Books Where Author = :author', { author: 'David' });
+     */
+    static async execute(sql, values) {
+        if (!connectionPool) await setupConnectionPool();
+
+        const t1 = performance.now();
+
+        const [ rows, fields ] =  await connectionPool.execute(sql, values);
+
+        const t2 = performance.now();
+        debug('execute', `${(t2-t1).toFixed(0).padStart(3, ' ')}ms`, sql.trim().split('\n')[0]+(sql.trim().split('\n').length>1?'...':''), `×${rows.length}`);
+
+        return [ rows, fields ];
+    }
+
     /**
      * Get a connection to the database.
      *