mySQL - 如何正确编写SELECT语句

Question

I have a mySQL SELECT statement with a combination of full text search and normal search in the WHERE condition and an additional JOIN like this

SELECT 
 customer.*, 
 countries.name as country
 FROM customer  
 LEFT JOIN countries ON countries.ID = customer.country_id 
 WHERE customer.num   = :keyword 
    OR customer.city  = :keyword  
    OR customer.email = :keyword 
    OR MATCH (customer.company) AGAINST (:keyword)
    OR countries.name = :keyword

Queries with a full text search into (customer.company) column returns no result as long as the table.column countries.name is part of the WHERE condition. But queries into countries.name itself are successful.

How to code the SELECT statement correctly to return a successful query using a combination of all WHERE components from above example ?

EDIT :

In a previous version I used this statment

 SELECT 
  customer.* ,
  countries.name
  FROM customer, countries 
  WHERE customer.country_id=countries.ID 
  AND MATCH (customer.company) AGAINST (:keyword)

  UNION

  SELECT 
  customer.*, 
  countries.name
  FROM customer, countries 
  WHERE customer.country_id=countries.ID 
  AND countries.name=:keyword

which works well. I just do not know if this is the efficient way to query two tables with different searchs (full text and normal). Also when I search in more than 2 columns the code is getting blown up easily, which I would like to avoid.

Any more ideas and help is welcome

Answer 1

You should check for NULLs since you are using a LEFT JOIN :

SELECT 
     customer.*, 
     countries.name as country
 FROM customer  
 LEFT JOIN countries ON countries.ID = customer.country_id 
 WHERE customer.num   = :keyword 
    OR customer.city  = :keyword  
    OR customer.email = :keyword 
    OR MATCH (customer.company) AGAINST (:keyword)
    OR (countries.name = :keyword OR countries.name IS NULL)

Just for clarification, conditions on the right table of a LEFT JOIN should be placed only inside the ON clause, not the WHERE clause . This is a bit different, since you want to compare it against all the other conditions, therefore - the NULL comparison.

Answer 2

My solution is just set a default value = '' to countries.name if it's null using CASE WHEN

(CASE WHEN countries.name is null then 'default value' else countries.name END)

new query

SELECT 
 customer.*, 
 countries.name as country
 FROM customer  
 LEFT JOIN countries ON countries.ID = customer.country_id 
 WHERE customer.num   = :keyword 
    OR customer.city  = :keyword  
    OR customer.email = :keyword 
    OR MATCH (customer.company) AGAINST (:keyword)
    OR (CASE WHEN countries.name is null then '' else countries.name END) = :keyword