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copied!<p><code>SIZE</code> is a reserved keyword. That means we cannot use it as an identifier (unless we put it in double quotes, but <a href="https://stackoverflow.com/a/6030439/146325">double-quoted identifiers are Teh Suck!</a> so don't do that). Change the column name to <code>ROOMSIZE</code> and <a href="http://www.sqlfiddle.com/#!4/616b3" rel="nofollow noreferrer">your statement will run</a>.</p> <p>Note that <code>TYPE</code> is also a keyword but not reserved. So we are allowed to use it as a column identifier. Types weren't introduced until 8; making <code>TYPE</code> a reserved keyword would have broken code in Oracle applications all over the world, not least in its own data dictionary.</p> <p>The documentation has a complete list of the reserved words. <a href="http://docs.oracle.com/cd/E11882_01/server.112/e41084/ap_keywd001.htm#BABCJAEB" rel="nofollow noreferrer">Find it here</a>.</p> <hr> <p>Why would using <code>"SIZE"</code> be such a bad idea? After all, as @JavaBeginner says, the SQL standard does permit it.</p> <p>Once we choose to use double-quotes to get around Oracle's naming rules we are condemned to use them <em>whenever</em> we reference the column. Hence this would not be a valid query:</p> <pre><code> select no_room, size from room where size > 10 </code></pre> <p>We would have to write instead:</p> <pre><code> select no_room, "SIZE" from room where "SIZE" > 10 </code></pre> <p>And it always have to be <code>"SIZE"</code>: <code>"size"</code> is a different identifier. so is <code>"Size"</code>.</p> <p>Best practice is the informed interpretation of what the standards permit. SQL allows us to do things which we shouldn't do if we want to build a robust and maintainable database. Not using double-quoted identifiers falls into that category. </p>

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