从数据库表中获取随机记录，并在mysql中进行多次检查？

Question

I have database table named ' ads '.i want to show these ads on the the websites randomly.My table structure is

user_id                 int(11)              
type                    varchar(50)             
title                   varchar(100)         
body                    varchar(100)           
display_url             varchar(100)           
target_url              varchar(100)       
dimension               varchar(50)    
image                   varchar(200)    
preferred_countries     text                  
preferred_languages     text                    
preferred_sites         text                  
excluded_sites          text                
preferred_keywords      text                
excluded_keywords       text                  
preferred_devices       varchar(100)      
schedule                mediumtext            
clicks                  int(20)              
clicked                 int(11)                
cpc                     decimal(20,20)    

As you can see there are columns like preferred_countries , preferred_languages , preferred_devices etc. I want to show these ads to a visitor by applying multiple checks like if there is prefered country for any ad then it will be shown to the visitor of that specific country and so on. I have fetched all the data related to user ie. visitor's country, visitor's language etc

But i am not getting any idea how to fetch the records like this.

Answer 1

select * from ads
where preferred_countries = $mycountry
order by rand()
limit 1

Answer 2

try this

select * from ads
where preferred_countries = $mycountry and preferred_languages=$language
order by rand()
limit 1

Answer 3

You could consider MySQL's RAND() function combined with an ORDER BY FIELD()

SELECT * FROM `ads` 
ORDER BY FIELD(preferred_countries, '$mycountry') DESC, RAND()
LIMIT 1

This won't filter out rows that don't match $mycountry, but if they exist, you'll get them first. You should also get a random result if there is more than one match.

Of course this won't work as well if your preferred_countries field might contain multiple country names.