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    <p>Well, this <em>may</em> have point on large databases, when you need <strong>fast</strong> responce on <strong>massive</strong> <code>DML</code> (<code>INSERT / UPDATE / DELETE</code>).</p> <p>The problem is that if you rely on database's way to ensure integrity, you hardly can optimize it.</p> <p>There is also thing called <code>SQL/PLSQL context switching</code> in <code>Oracle</code>: if you create an <strong>empty</strong> trigger on the table, it will slow down <code>DML</code> about 20 times — with the mere fact that the trigger exists.</p> <p>In Oracle, when you write a <code>ON UPDATE</code> trigger and update <code>50,000</code> rows in the table, the trigger and the query in it gets called <code>50,000</code> times. Foreign keys perform better, but they may also get laggy (and you can do nothing with the underlying queries)</p> <p>In this case, it's better to put the results you want to update into a temporary table, issue a <code>MERGE</code>, check integrity before and after, and apply the business rules. A single query that processes <code>50,000</code> rows works faster than a loop of <code>50,000</code> queries processing single row.</p> <p>Of course, it's very hard to implement and only pays for itself when you have <em>really</em> large database and need to perform <em>really</em> massive updates on it.</p> <p>In <code>Oracle</code>, in any case, <code>FOREING KEY</code> constraints perform better than tiggers implementing the same functionality.</p> <p><code>PRIMARY KEYS</code> will most likely improve performance, as a primary key implies creating the <code>UNIQUE INDEX</code> on the constrained field, and this index may be efficiently used in the queries. A <code>UNIQUE INDEX</code> is also a natural and most efficent way to enforce uniqueness.</p> <p>But of course, as any index, is slows down <code>INSERTS</code> and those <code>UPDATES</code> and <code>DELETES</code> whose <code>WHERE</code> condition is not selective.</p> <p>I. e. if you need to <code>UPDATE</code> or <code>DELETE</code> <code>1</code> row of <code>2,000,000</code>, then the index is your friend; if you need to <code>UPDATE</code> or <code>DELETE</code> <code>1,500,000</code> rows of <code>2,000,000</code>, the index is your enemy. It's a matter of tradeoff.</p> <p>You may also see my answer <a href="https://stackoverflow.com/questions/543274/is-it-a-best-practise-for-a-database-to-allow-apps-do-crud-operations-always-thro/543503#543503"><strong>here</strong></a>.</p>
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    1. POHave you ever worked with Database no "Relations", no "PKs", and no "FKs", just raw data?
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    1. USQuassnoi
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    1. POHave you ever worked with Database no "Relations", no "PKs", and no "FKs", just raw data?
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    1. COWhat I got from my friend that they depends on using triggers to ensure integrity, so we can talk about massive number of triggers in large databases, this will kill the applcation performance, so using PKs, FKs, will improve performance, right?
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    2. COFK's do not improve performance at all, they are pure check constraints. PK's will most likely improve performance, as they are indexes that may speed up the queries.
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    3. COBut compared to triggers, FK's will most likely improve performance, if we talk of Oracle.
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