Query Plan

<br /><p><font face="Arial" size="2">Have a question regarding when a Query Plan uses an Index.</font><p><font
face="Arial"size="2">I have a basic statement</font><p><font face="Arial" size="2">This query uses the Index
Scan:</font><br/><font face="Arial" size="2">explain analyse select * from tablea where columna_id <
57</font><p><fontface="Arial" size="2">This query uses Seq Scan:</font><br /><font face="Arial" size="2">explain
analyseselect * from tablea where columna_id < 58</font><p><font face="Arial" size="2">There are about 5000 records
inthis table, and columna_id is the primary key, which is Indexed... And recently recreated.</font><p><font
face="Arial"size="2">My question is why is the Plan not using the index on the second occasions?</font><p><font
face="Arial"size="2">Theo</font><table><tr><td bgcolor="#ffffff"><font
color="#000000">______________________________________________________________________<br/>This email, including
attachments,is intended only for the addressee<br />and may be confidential, privileged and subject to copyright. If
you<br/>have received this email in error, please advise the sender and delete<br />it. If you are not the intended
recipientof this email, you must not<br />use, copy or disclose its content to anyone. You must not copy or <br
/>communicateto others content that is confidential or subject to <br />copyright, unless you have the consent of the
contentowner.<br /></font></td></tr></table>