How to simplify following SQL query to invoke count method only once?
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I have following SQL code
select surname, (select count(surname)) from employees group by surname having count(surname) > 1 order by surname asc;
I need to invoke count method only once.
There are a million ways to do that, but as Gordon pointed out: you shouldn't worry with count being executed multiple times - let the database take care of it. But if you somehow want to avoid writing it twice, try these options:
SELECT * FROM (SELECT surname, count(surname) AS c FROM employees GROUP BY surname) j WHERE c > 1 ORDER BY surname
Or a CTE
WITH j AS ( SELECT surname, count(surname) AS c FROM employees GROUP BY surname) SELECT * FROM j WHERE c > 1 ORDER BY surname
How to Execute a SQL Query Only if Another SQL Query has no , If that predicate returns no rows, they wanted to run another query using a different predicate. The following query is formally correct and runs without any enough to avoid the second query, because the first one does yield 9 rows. 3 If the count is null/zero return the second value, otherwise the first The SQL COUNT(), AVG() and SUM() Functions. The COUNT() function returns the number of rows that matches a specified criterion. The AVG() function returns the average value of a numeric column. The SUM() function returns the total sum of a numeric column. COUNT() Syntax
This uses count() only once but uses a subquery
SELECT * FROM ( SELECT surname ,count(surname) as surname_count FROM employees GROUP BY surname ) WHERE surname_count > 1 ORDER BY surname ASC
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- Don't worry about using
count()more than once. Let the database worry about optimization.
- As Gordon Linoff notes, you don't need to bother with
count(). And you don't need the sub-select. Just
select surname, count(surname) from employees group by surname having count(surname) > 1 order by surname;
- On sqlfiddle it doesn't work .
- Thank you guys, Jim Jones answer's works perfectly. But my code with two duplicates show my poor knowledge about sql, i'm right? ;>