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| bio | website | |
|---|---|---|
| location | Munich | |
| age | ||
| visits | member for | 2 years |
| seen | 3 mins ago | |
| stats | profile views | 733 |
I'm looking for job as a software developer (Java) with focus on relational database technologies (Oracle, PostgreSQL)
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Apr 25 |
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Combine multiple queries into single query You might want to add a column that identifies the "source" of each row to be able to distinguish between driver, freight and locomotive. |
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Apr 25 |
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Combine multiple queries into single query Why the group by you are not aggregating? You are also missing join conditions (preferrably using using standard SQL 92 JOINs) |
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Apr 25 |
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Are database query optimizers aware of storage performance differences? Oracle generates "system statistics" which measure (amongst other things) the latency (and performance) of the disk access and includes those values into the plan. For Postgres you can manually set a scale on how "expensive" certain IO operations which is also used by the planner. |
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Apr 24 |
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“Rewinding” a Postgresql database You could use point in time recovery to restore a backup to a specific time: postgresql.org/docs/current/static/continuous-archiving.html |
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Apr 24 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry @Colin'tHart: I know ;) I just didn't want to introduce too many new things (And I wanted to somehow stay close to the original query). |
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Apr 24 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry @Douglas: hv is an alias for the derived table (aka "sub-query"). And you are right, I forgot the alias inside the derived table. |
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Apr 24 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry @Douglas: "common-sense" is nothing you can put into code. So Postgres (or any other DBMS I would assume) can only use the information that is available in the metadata - which is the PK information. |
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Apr 24 |
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How to snapshot or version a relational database when data changes? Which DBMS are you using? Oracle has "flashback" queries and DB2 (10.1) has "time travel" queries. Both store historical data in separate tables, so the performance of queries for the "current" data is not affected |
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Apr 23 |
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Storing data as rows as opposed to columns If you are using Postgres, have a look at hstore. It is essentially a key/value store (or to go with the hype: a NoSQL) which will make this kind of dynamic attribute much easier to deal with. |
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Apr 23 |
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Why PostreSQL 9.2 does not use index scan if it can? Did you analyze the table. Maybe you have wrong statistics |
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Apr 23 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry @Douglas: using window functions might give you a better performance. You can compare the execution plans to find out which one is more efficient. |
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Apr 23 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry which Postgres 9.1 (and later) does: postgresql.org/docs/current/static/sql-select.html#SQL-GROUPBY |
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Apr 23 |
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need the most efficient way to handle unique constraint errors You can use log errors into together with the insert statement. Don't know if that is compatible with the APPEND hint though: docs.oracle.com/cd/E11882_01/server.112/e26088/… |
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Apr 23 |
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Following procedure generates an error and I cannot find the reason Please edit your question. Posting unreadable code in the comments makes it even worse. |
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Apr 23 |
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Error “column does not exist” in a SELECT with JOIN and GROUP BY querry "does not authorize to use the columns in the SELECT clause if they do not appears in the GROUP BY clause" so does every other sensible DBMS. |
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Apr 23 |
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How Can I do and INNER JOIN USING (2 columns)? What happened when you tried? |
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Apr 23 |
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Following procedure generates an error and I cannot find the reason And the error is? |
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Apr 23 |
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Oracle SUM - ORA-00937: not a single-group group function @Colin'tHart: it's not clear for me from the original question what David wants. So I copied all the columns from the original SELECT. I agree that it's very likely that this is not what he is after - your answer is probably the way to go. |
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Apr 23 |
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How to properly format sqlite shell output? re 2: you might try henplus or SQL Workbench/J. Both are Java/JDBC based and should work with SQLite. henplus.sourceforge.net sql-workbench.net |
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Apr 22 |
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Storing data in PostgreSQL: One table or two? Which is a piece of cake using the range type and exclusion constraints.... |
