GROUP BY : SQL Aggregation for Common Values

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sql server Group by with calculated values

I have two tables: costumer table and invoice table. How to calculate sum(value) for each costumer (id) when I have calculated variables in group by statement - without puting code for calculated ...
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GROUP BY performance

I have a query like this: SELECT HOUR(datetime) as Hour, COUNT(*) as hits, SUM(clicks) FROM visitors_log_table WHERE datetime >= CURDATE() GROUP BY Hour WITH ROLLUP It works fine. But I ...
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Should I group by and then join, or join and then group by?

(oracle's optimizer does the same thing for both approaches when just two tables are involved, thus my question involves three tables) Assume three tables t1, t2 and t3 with a pairwise 1:n ...
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How to index for a group by with columns from different tables?

Is it possible to create an index from columns of 2 different tables? If not, how do we optimize a query that does a group by on columns of 2 different tables? For example: the following ...
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MySQL GROUP BY and ORDER BY giving inconsistent results

I'm currently working with WordPress, and I've added a new meta value which is a number between 0 and 30. Zero is ignored and up to 30 need to be organised in order and only the latest (based on the ...
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Generate report from visitor counter

I have a visitor counter, the table looks like this: id | country_code | datetime | Browser | ... --------------------------------------------------------- 1 | FR | ...
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group by and order by making query very slow in mysql?

Query works fast: select SQL_NO_CACHE users.id, users.name from useres left join user_statistics on users.id = user_statistics.user_id where users.is_deleted = 0 group by users.id ...
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Is it possible to group by a fraction of the result set?

I have a database of products with prices. What I'd like to be able to do is figure out 5 different price ranges such that each range, when ordered by price, will have approximately the same number of ...
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How can I number my groups using an Access “Find Duplicates” Query?

I have a query created by the MS Access 2010 find duplicates wizard. It is: SELECT * FROM fbExpenses WHERE [expense_date] In (SELECT [expense_date] FROM [fbExpenses] As ...
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Select Foo object without any specific Bar events

Consider two tables: Foo: id INT, name VARCHAR Bar: id INT, foo_id INT REFERENCES Foo(id), event_type VARCHAR DEFAULT NULL, event_duration INT DEFAULT NULL Each Foo item can have ...
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is it good to add index on column used in group by clause?

I have a query like- select x, sum(y) from xyz where z>=100 group by x order by sum(y) desc; will it be faster if I am going to add index on x?
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can this mysql query be optimized further?

I have this query select counterparty_id, max(id) max_id from client_administrations where counterparty_type = 1 and effective_on <= '2013-10-22' group by counterparty_id When I ...