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POmySQL many to many relation with all members of a group having a common attribute
 

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  1. POmySQL many to many relation with all members of a group having a common attribute
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    <p>Is it possible to have a many to many relationship between two tables, and enforce that all the members of a group are to have a particular attribute in common?</p> <p>For example, a worker can be in several groups, and a group can have several workers, but all the workers in a group must be on the same site. There are enough workers and sites that I can't make a new table for each site.</p> <p>--EDIT--</p> <p>This is the simplified schema. I'm using mySQL workbench, but I think this is right:</p> <pre><code>-- ----------------------------------------------------- -- Table `DB`.`Worker` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `DB`.`Worker` ( `workerID` INT NOT NULL , `site` VARCHAR(45) , PRIMARY KEY (`workerID`) ; -- ----------------------------------------------------- -- Table `DB`.`Group` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `DB`.`Group` ( `groupID` INT NOT NULL , PRIMARY KEY (`groupID`) ; -- ----------------------------------------------------- -- Table `DB`.`Worker_Group` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `DB`.`workerGroup` ( `workerID` INT NOT NULL , `groupID` INT NOT NULL , PRIMARY KEY (`workerID`, `groupID`) , INDEX `fk_Group` (`groupID` ASC) , CONSTRAINT `fk_Worker` FOREIGN KEY (`workerID` ) REFERENCES `DB`.`Worker` (`workerID` ) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `fk_Group` FOREIGN KEY (`groupID`) REFERENCES `DB`.`Group` (`groupID`) ON DELETE NO ACTION ON UPDATE NO ACTION) ; </code></pre>
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    1. USDenverCoder8
    1. USDenverCoder8
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      1. VTUpMod
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    1. COCan you post the schemas?
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      1. USGirish Rao
    2. COArg, nearly done writing an answer and your edit introduces a new constraint: A worker can only be related to one site.
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      1. USMatBailie
    3. COAh sorry, I didn't realise that would make a difference! I'm fairly new to sql.
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      1. USDenverCoder8
 

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