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POWhich columns should I add to a PRIMARY KEY
 

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  1. POWhich columns should I add to a PRIMARY KEY
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    <p>I want to create a table and avoid duplicated entries, by creating a PRIMARY KEY. The problem is I don't know which columns I should add to this KEY. Consider the next table:</p> <pre><code>CREATE TABLE `customers` ( `id_c` int(11) unsigned NOT NULL, `lang` tinyint(2) unsigned NOT NULL, `name` varchar(80) collate utf8_unicode_ci NOT NULL, `franchise` int(11) unsigned NOT NULL, KEY `id_c` (`id_c`), KEY `lang` (`lang`), KEY `franchise` (`franchise`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; </code></pre> <p><strong>id_c</strong>: Id of customer. It can be an enterprise. Suppose <em>McDonald's</em><br> <strong>lang</strong>: Contact language.<br> <strong>boss</strong>: Boss' name<br> <strong>franchise</strong>: If not zero, it is a franchise. McDonald's in Rome, Paris, London...<br><br> As you can see, each <strong>ENTERPRISE</strong> can have different <strong>central</strong> "shops" in each country (<em>contact language</em>), but also different <strong><em>franchises</em></strong> in each city (where boss' name would be different).<br><br> I want to be able to INSERT new rows where the <strong>id_c</strong>, <strong>lang</strong> can be not-distinct (many franchises in same country). But <strong>name</strong> has to be distinct only if (<strong>id_c,lang</strong>) is the same (for other id_c,lang combination... name could be the same). And franchise can be the same too only if it has not been assigned in the same (id_c,lang) pair. <br><br> I was thinking about a PRIMARY KEY (<code>lang</code>,<code>name</code>), but it might not be the best way. Is this table structure just too complex?</p>
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