Difference between revisions of "Forgotten rows"

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Line 26: Line 26:
 
  GROUP BY name
 
  GROUP BY name
 
<p>In order to obtain the rows where the count from the query is 0 a
 
<p>In order to obtain the rows where the count from the query is 0 a
LEFT JOIN or a UNION can be used.</p>
+
<code>LEFT JOIN</code> or a <code>UNION</code> can be used.</p>
 
</div>
 
</div>
 
<source lang='sql' class='def'> SELECT name, COUNT(*)
 
<source lang='sql' class='def'> SELECT name, COUNT(*)

Revision as of 14:39, 30 July 2012

Include the rows your JOIN forgot.

schema:scott
DROP TABLE customer;
DROP TABLE invoice;
 CREATE TABLE customer(
  id INTEGER,
  name VARCHAR(20));
INSERT INTO customer VALUES (1,'Betty');
INSERT INTO customer VALUES (2,'Robert');
INSERT INTO customer VALUES (3,'Janette');
CREATE TABLE invoice(
  invoiceno INTEGER,
  whn DATE,
  custid INTEGER,
  cost INTEGER );
INSERT INTO invoice VALUES (1,(2006,11,01),1,100);
INSERT INTO invoice VALUES (2,(2006,11,05),1,500);
INSERT INTO invoice VALUES (3,(2006,11,11),3,200);

The following query will only give two rows as the JOIN function automatically does not include rows with a count of 0.

SELECT name, COUNT(*)
FROM customer JOIN invoice ON (id=custid)
GROUP BY name

In order to obtain the rows where the count from the query is 0 a LEFT JOIN or a UNION can be used.

 SELECT name, COUNT(*)
 FROM customer LEFT JOIN invoice ON (id=custid)
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