Case when in MySQL returns multiple field processing schemes

Problem specification

     In general case when structure , Only one field can be returned , But there are many business scenarios that need to return more than one field . There are two solutions to this problem , One is to case when The structure is transformed , Support to return multiple fields ; The other is to keep case when The number of return fields remains unchanged ( Only one field is returned ), Modify business logic , stay service According to the in case when Return a field for processing . This paper mainly introduces the first treatment scheme . Here is a business scenario to illustrate how to handle .

Business problem scenario description

     Now there is a platform for job recruitment , The recruiter will send the invitation notice sent by resume , As a job seeker, there are three return States ,1. Receive resume and send invitation .2. Reject the invitation to send resume , Fill in the rejection reason (1. Too far away ;2. Found a job ;3. other );3. Do not process the received information , Neither accept nor refuse . Need one sql The query needs to return two fields : Whether to accept the invitation to send resume , Three states :1. receive ,2. Refuse ,3. Don't deal with it ; Rejection status :0. No rejection processing ;1. Too far away ;2. Found a job ;3. other . Only when the applicant refuses to send the resume, the rejection status will change from 1-3 Value in , When receiving resume and sending invitation or not processing, this status needs to be returned 0.
     Brief description of business table :job_send_post Send the resume record form for the job seeker , As long as the applicant has sent a resume, records will be added to this form ;job_news Record the information sent to the recruiter for the job seeker .

Processing mode

    case when Only one field is allowed to be returned , If you don't support it, you can only do it yourself " New fields ", So you can use concat Function , This splicing can support splicing multiple fields . The summary is written as follows ：

CASE WHEN 
	 Conditions 
THEN CONCAT( Field 1,'+', Field 2,'+', Field 3......)
ELSE CONCAT( Field 1,'+', Field 2,'+', Field 3......)
END

--  Query whether the job search end has sent a rejection resume message and the rejection type in the recruitment end message record , If it is not sent, the resume invitation status is 3, Reject status is 0. If yes, the resume invitation status is 2, The reason for rejection is found by using refuse_type Reject type 
IFNULL((SELECT CONCAT(2,"+",refuse_type) FROM job_news WHERE user_id='rxkyogtktutm4pbsi18e' ),CONCAT(3,'+',0))

END) receive_state
     In this scenario, it is necessary to splice the accept invitation field and the reject status field , Note that a special character needs to be used in the middle of the field for splicing , convenient service Layer to intercept . The specific implementation is as follows :

	SELECT 
(CASE WHEN 
--  Judge user_id by rxkyogtktutm4pbsi18e Has the applicant submitted resume records to the recruitment end , If it has been delivered, it means that it has accepted the resume invitation of the recruitment end , Resume invitation status is 1, Reject status is 0
 IF((SELECT 1 FROM job_send_post WHERE user_id='rxkyogtktutm4pbsi18e' LIMIT 1)=1,TRUE,FALSE)
THEN
	CONCAT(1,'+',0)
ELSE
	--  Query whether the job search end has sent a rejection resume message and the rejection type in the recruitment end message record , If it is not sent, the resume invitation status is 3, Reject status is 0. If yes, the resume invitation status is 2, The reason for rejection is found by using refuse_type Reject type 
	IFNULL((SELECT CONCAT(2,"+",refuse_type) FROM job_news WHERE user_id='rxkyogtktutm4pbsi18e' ),CONCAT(3,'+',0))
END) receive_state

     The above is the process of dealing with problems , If help , Welcome to like or leave a message !