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POSQL: Complex Deletion
 

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    <p>I basically created some tables to play around with: I have Two main tables, and a Many-Many join table. Here is the DDL: (I am using HSQLDB)</p> <pre><code>CREATE TABLE PERSON ( PERSON_ID INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, NAME VARCHAR(50), MAIN_PERSON_ID INTEGER ) CREATE TABLE JOB ( JOB_ID INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, NAME VARCHAR(50) ) CREATE TABLE JOB_PERSON ( PERSON_ID INTEGER, JOB_ID INTEGER ) ALTER TABLE JOB_PERSON ADD CONSTRAINT FK_PERSON_JOB FOREIGN KEY(PERSON_ID) REFERENCES PERSON ON DELETE CASCADE ON UPDATE CASCADE ALTER TABLE JOB_PERSON ADD CONSTRAINT FK_JOB_PERSON FOREIGN KEY(JOB_ID) REFERENCES JOB ON DELETE CASCADE ON UPDATE CASCADE ALTER TABLE PERSON ADD CONSTRAINT FK_PERSON_PERSON FOREIGN KEY(MAIN_PERSON_ID) REFERENCES PERSON ON DELETE CASCADE ON UPDATE CASCADE insert into person values(null,'Arthur', null); insert into person values(null,'James',0); insert into job values(null, 'Programmer') insert into job values(null, 'Manager') insert into job_person values(0,0); insert into job_person values(0,1); insert into job_person values(1,1); </code></pre> <p>I want to create a delete statement that deletes orphans from JOB (if there exists only one entry in the join table for a specific job) based on the PERSON.PERSON_ID. </p> <p>In pseudo language: </p> <pre><code>delete from job where job_person.job_id=job.job_id AND count(job_person.job_id)=1 AND job_person.person_id=X </code></pre> <p>Where X is some person_id. I have tried a lot of different ways; I think it is the "COUNT" part that is causing problems. I am an SQL rookie, so any help would be much appreciated.</p>
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    1. USChristian Strempfer
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    1. COI'm not entirely clear on the question. Orphans in the job table would have no corresponding entry in the job_person table.
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      1. USDave
    2. COAccording to Dave i don't understand why you are try to delete data which are used by an other table...
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      1. USFred
    3. COThis is the functionality I was looking for: DELETE FROM JOB WHERE JOB_ID NOT IN ( SELECT JOB_ID FROM JOB_PERSON )
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