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You can update existing rows using the
<code class="command">UPDATE</code> command.
Suppose you discover the temperature readings are
all off by 2 degrees after November 28. You can correct the
data as follows:
</p><pre class="programlisting">
UPDATE weather
SET temp_hi = temp_hi - 2, temp_lo = temp_lo - 2
WHERE date > '1994-11-28';
</pre><p>
</p><p>
Look at the new state of the data:
</p><pre class="programlisting">
SELECT * FROM weather;
city | temp_lo | temp_hi | prcp | date
---------------+---------+---------+------+------------
San Francisco | 46 | 50 | 0.25 | 1994-11-27
San Francisco | 41 | 55 | 0 | 1994-11-29
Hayward | 35 | 52 | | 1994-11-29
(3 rows)
</pre><p>
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