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POMYSQL: How do I create a trigger that calculates a field value based on value from different table?
 

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  1. POMYSQL: How do I create a trigger that calculates a field value based on value from different table?
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    <p>In <em>table A</em> I have fields <code>CENA</code>(price), <code>cena_za_kus</code>(price_per_piece), <code>mnozstvi</code>(quantity).<br> In <em>table B</em> I have field <code>DPH</code>(vat).</p> <p>I'd like to add a before update/insert trigger, which would calculate the value of <code>PRICE</code> field, something like this: </p> <pre><code>price = (price_per_piece * count) + (price_per_piece * count * tableB.vat) </code></pre> <p>Is this possible? Thank you.</p> <p>Edit: And the row in <em>table</em> A has a foreign_key <code>dph_id</code> pointing to the corresponding row in <em>table B</em>.</p> <pre><code> CREATE TABLE `polozky` ( `id` int(11) NOT NULL AUTO_INCREMENT, `objednavka_id` int(11) NOT NULL, `dph_id` int(11) NOT NULL, `polozka` varchar(64) COLLATE utf8_unicode_ci NOT NULL, `cena` float NOT NULL, `mnozstvi` int(11) NOT NULL, `cena_za_kus` float NOT NULL, PRIMARY KEY (`id`), KEY `IdObjednavka` (`objednavka_id`,`dph_id`), KEY `objednavka_id` (`objednavka_id`), KEY `dph_id` (`dph_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=63663 ; ALTER TABLE `polozky` ADD CONSTRAINT `polozky_ibfk_7` FOREIGN KEY (`objednavka_id`) REFERENCES `objednavky` (`id`) ON DELETE CASCADE ON UPDATE CASCADE, ADD CONSTRAINT `polozky_ibfk_8` FOREIGN KEY (`dph_id`) REFERENCES `dph` (`id`) ON DELETE CASCADE ON UPDATE CASCADE; </code></pre> <p>and </p> <pre><code>CREATE TABLE `dph` ( `id` int(11) NOT NULL AUTO_INCREMENT, `sekce` varchar(64) COLLATE utf8_unicode_ci NOT NULL DEFAULT 'nastaveni', `popis` varchar(8) COLLATE utf8_unicode_ci NOT NULL, `DPH` int(11) unsigned NOT NULL, `poradi` int(11) unsigned NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `DPH_2` (`DPH`), UNIQUE KEY `popis` (`popis`), KEY `DPH` (`DPH`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=9 ; </code></pre>
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    1. USuser1848605
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      1. POMYSQL: How do I create a trigger that calculates a field value based on value from different table?
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      1. VTUpMod
    1. COshare the table schema of tables involved; use `show create table tableName`.
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      1. POMYSQL: How do I create a trigger that calculates a field value based on value from different table?
      1. USSparKot
    2. COYou have `cena` or price defined in the table you want the trigger to run on and as not null. If price is a derived/calculate value, then why store it. Just calculate on an as needed basis. If you really need it then I would suggest a view. `CREATE VIEW v AS SELECT qty, price, qty*price AS value FROM t;`
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      1. USHarrison
    3. COHarrison: Is it not better to calculate the value in database with trigger instead of having to calcualate it manually every time in PHP?
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      1. POMYSQL: How do I create a trigger that calculates a field value based on value from different table?
      1. USuser1848605
 

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