Just a small correction: there should be <font color="blue">time</font>::<font
color="blue">text</font>>>><fontcolor="red">'prev_time'</font> for the calculations to be correct:<br /><pre
class="src"><fontcolor="blue"><br />
select</font> *<br /> <font color="blue">from</font> (<br /> <font color="blue">select</font> (((<font
color="magenta">case</font><font color="blue">when</font> <font color="blue">time</font>::<font
color="blue">text</font>= <<<<font color="red">'prev_time'</font> <font color="blue">then</font> <font
color="darkblue"><b>0</b></font><font color="blue">else</font> <font color="darkblue"><b>1</b></font> <font
color="blue">end</font>)+(<<<<fontcolor="red">'dense_rank'</font>)::int4)::<font
color="blue">text</font>>>><fontcolor="red">'dense_rank'</font>)::int4 <font color="blue">as</font> position,
runnerid,<font color="blue">time</font>, <font color="blue">time</font>::<font
color="blue">text</font>>>><fontcolor="red">'prev_time'</font><br /> <font color="blue">from</font>
big_marathon<br/> <font color="blue">order</font> <font color="blue">by</font> <font color="blue">time</font><br
/> ) results<br /> <font color="blue">where</font> position=<font color="darkblue"><b>2</b></font><br />
</pre><pre class="src"><font color="teal">-- meter_readings</font><br /><font color="blue">select</font> <font
color="red">''</font>>>> <font color="red">'lag'</font>;<br /><br /><font color="blue">select</font> <font
color="blue">date</font>,reading::<font color="blue">numeric</font>-(<font color="magenta">case</font> lag <font
color="blue">when</font><font color="red">''</font> <font color="blue">then</font> <font color="#777777">null</font>
<fontcolor="blue">else</font> lag <font color="blue">end</font>)::<font color="blue">numeric</font> <font
color="blue">as</font>used<br /> <font color="blue">from</font> (<br /> <font color="blue">select</font> <font
color="blue">date</font>,<<<<font color="red">'lag'</font> <font color="blue">as</font> lag, reading::<font
color="blue">text</font>>>><font color="red">'lag'</font> <font color="blue">as</font> reading<br /> <font
color="blue">from</font>meter_readings<br /> <font color="blue">order</font> <font color="blue">by</font> <font
color="blue">date</font><br/> ) <font color="blue">as</font> t<br /> <font color="blue">order</font> <font
color="blue">by</font>used <font color="blue">asc</font> nulls <font color="blue">last</font> limit <font
color="darkblue"><b>1</b></font><br/>
</pre><br />Best regards,<br />Vladimir Sitnikov<br />