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    <p>When you <code>JOIN</code> two or more table together, you effectively get a cartesian product for these tables to which a filter stated in the <code>JOIN</code> condition is applied.</p> <p>This is more obvious when you use an obsolete implicit <code>JOIN</code> syntax.</p> <p>The <code>LEFT JOIN</code> guarantees that you get no <em>less</em> rows than the leftmost table contains, i. e. each row from the leftmost table is returned at least once.</p> <p>You can still get more rows, if the filter is not a one-to-one row mapping.</p> <p>In your case:</p> <pre><code>SELECT (b.descr || ' - ' || c.descr) description FROM tbl1 a LEFT JOIN tbl2 b ON b.ACCOUNT = a.ACCOUNT LEFT JOIN tbl3 c ON c.product = a.product WHERE a.descr50 = ' ' </code></pre> <p>either <code>acccount</code> or <code>product</code> are not unique in <code>b</code> or <code>c</code>.</p> <p>For these rows:</p> <pre><code>a.account 1 2 3 b.account b.description 1 Account 1 2 Account 2 - old 2 Account 2 - new </code></pre> <p>, the <code>JOIN</code> will return the following:</p> <pre><code>a.account b.account b.description 1 1 Account 1 2 2 Account 2 - old 2 2 Account 2 - new 3 NULL NULL </code></pre> <p>, giving you more rows than either of the tables contains.</p> <p>To just pick the first matching description from either table, use this:</p> <pre><code>SELECT ( SELECT FIRST_VALUE(descr) OVER (ORDER BY descr) FROM tbl2 b WHERE b.account = a.account AND rownum = 1 ) || ' - ' || ( SELECT FIRST_VALUE(descr) OVER (ORDER BY descr) FROM tbl3 c WHERE c.product= a.product AND rownum = 1 ) description FROM tbl1 a WHERE a.descr50 = ' ' </code></pre> <p>To update, just wrap the query into an inline view:</p> <pre><code>UPDATE ( SELECT ( SELECT FIRST_VALUE(descr) OVER (ORDER BY descr) FROM tbl2 b WHERE b.account = a.account AND rownum = 1 ) || ' - ' || ( SELECT FIRST_VALUE(descr) OVER (ORDER BY descr) FROM tbl3 c WHERE c.product= a.product AND rownum = 1 ) description FROM tbl1 a WHERE a.descr50 = ' ' ) SET descr50 = description </code></pre>
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    1. POGetting extra rows - After joing the 3 tables using Left Join
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    1. COThanks for your explanation. My requiremetn is to fill the table1 field called description by concatinating the description from the table2 and table3. But the common field between 1 and 2 is account and 1 and 3 is product. Can you please help me in this ?
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    2. COI cant update directly, i have to check it then only i can update. That y i am using select to get the values but its is more that the values in the table1. but only 27.
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    3. CO@Prem: I updated the post with sample data. Given that `b` contains more than one description for account `2`, which description you want account `2` to have?
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