New answers tagged join
0
votes
Select tables data with sum of other tables
Think through it this way it will be executed:
JOIN the user and history tables together. Imagine the resulting "table" that contains all combinations of rows -- based on ON, which ...
- 74.7k
3
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SQL Server 2014 Cardinality Estimator estimate final number of rows after OUTER JOIN is less than number of rows from initial table
Cardinality Estimation is just an estimation. Many times it won't be the exact number of rows, for a multitude of reasons. But if it is, great, that means the SQL Engine was able to do its job ...
- 31.7k
1
vote
Accepted
Join order and nullability
Based on some experimentation and my understanding of how join order works in Postgres, I think the following rules can be applied:
Note: in the diagrams below, ! denotes not nullable, ∅ denotes ...
- 223
-1
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Join order and nullability
When working with the results of a database query inside a statically typed application, we need to know whether a particular column could return null or not.
No, you do not. You need to know if the ...
- 594
2
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ORA-12015 materialized view complex query error with simple join two table
5.2.2 About Materialized Views Containing Only Joins
If you specify REFRESH FAST, Oracle Database performs further
verification of the query definition to ensure that fast refresh can
be performed if ...
- 39.5k
3
votes
Accepted
Worst performance multiple left join big tables after restore DB
Duplicate indexes
For starters, it certainly does not help that you duplicated most of your indexes. Your setup is struggling with insufficient cache as indicated by the large numbers of read's in the ...
- 167k
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