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ROW_NUMBER() in MySQL
... kind of isn't).
I often plump for a null-self-join:
SELECT t0.col3
FROM table AS t0
LEFT JOIN table AS t1 ON t0.col1=t1.col1 AND t0.col2=t1.col2 AND t1.col3>t0.col3
WHERE t1.col1 IS NULL;
“Get the rows in the table for which no other row with matching col1,col2 has a higher col3.” (You w...
How do HashTables deal with collisions?
I've heard in my degree classes that a HashTable will place a new entry into the 'next available' bucket if the new Key entry collides with another.
...
Best practices for in-app database migration for Sqlite
...anges aren't committed.
For making schema changes, sqlite supports "ALTER TABLE" syntax for certain operations (renaming the table or adding a column). This is an easy way to update existing tables in-place. See the documentation here: http://www.sqlite.org/lang_altertable.html. For deleting col...
Entity Framework - Invalid Column Name '*_ID"
...
What I have figured out is when you have an ICollection that references a table and there is no column that it can figure out, it creates one for you to try to make the connection between the tables. This specifically happens with ICollection and has driven me "batty" trying to figure it out.
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How can I alter a primary key constraint using SQL syntax?
I have a table that is missing a column in its primary key constraint. Instead of editing it through SQL Server, I want to put this in a script to add it as part of our update scripts.
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Add column to SQL Server
I need to add a column to my SQL Server table. Is it possible to do so without losing the data, I already have?
5 Answers...
How To Create Table with Identity Column
I have an existing table that I am about to blow away because I did not create it with the ID column set to be the table's Identity column.
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Adding 'serial' to existing column in Postgres
I have a small table (~30 rows) in my Postgres 9.0 database with an integer ID field (the primary key) which currently contains unique sequential integers starting at 1, but which was not created using the 'serial' keyword.
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INSERT INTO…SELECT for all MySQL columns
...The correct syntax is described in the manual. Try this:
INSERT INTO this_table_archive (col1, col2, ..., coln)
SELECT col1, col2, ..., coln
FROM this_table
WHERE entry_date < '2011-01-01 00:00:00';
If the id columns is an auto-increment column and you already have some data in both tables the...
MySQL select 10 random rows from 600K rows fast
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SELECT column FROM table
ORDER BY RAND()
LIMIT 10
Not the efficient solution but works
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