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Sorting arrays in NumPy by column
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You can sort on multiple columns as per Steve Tjoa's method by using a stable sort like mergesort and sorting the indices from the least significant to the most significant columns:
a = a[a[:,2].argsort()] # First sort doesn't need to be stable.
a = a[a[:,1].argsort(kind='mergesort')]
a = a[a[:,...
Delete all Duplicate Rows except for One in MySQL? [duplicate]
How would I delete all duplicate data from a MySQL Table?
2 Answers
2
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Why is early return slower than else?
...ashing works:
__builtins__ hashes to -1196389688 which reduced modulo the table size (32) means it is stored in the #8 slot of the table.
without_else hashes to 505688136 which reduced modulo 32 is 8 so there's a collision. To resolve this Python calculates:
Starting with:
j = hash % 32
perturb ...
Update multiple columns in SQL
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Try this:
UPDATE table1
SET a = t2.a, b = t2.b, .......
FROM table2 t2
WHERE table1.id = t2.id
That should work in most SQL dialects, excluding Oracle.
And yes - it's a lot of typing - it's the way SQL does this.
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FIND_IN_SET() vs IN()
I have 2 tables in my database. One is for orders, and one is for companies.
6 Answers
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How can I list all collections in the MongoDB shell?
...e current database that I'm using?
Three methods
show collections
show tables
db.getCollectionNames()
To list all databases:
show dbs
To enter or use a given database:
use databasename
To list all collections:
show collections
Output:
collection1
collection2
system.indexes
(o...
How can I select rows with most recent timestamp for each key value?
I have a table of sensor data. Each row has a sensor id, a timestamp, and other fields. I want to select a single row with latest timestamp for each sensor, including some of the other fields.
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Rails Model find where not equal
...User.where.not(user_id: me)
In Rails 3.x
GroupUser.where(GroupUser.arel_table[:user_id].not_eq(me))
To shorten the length, you could store GroupUser.arel_table in a variable or if using inside the model GroupUser itself e.g., in a scope, you can use arel_table[:user_id] instead of GroupUser.are...
What are the options for storing hierarchical data in a relational database? [closed]
...useful for managing hierarchical data:
the HierarchyId data type.
common table expressions, using the with keyword.
Have a look at "Model Your Data Hierarchies With SQL Server 2008" by Kent Tegels on MSDN for starts. See also my own question: Recursive same-table query in SQL Server 2008
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SQL中使用update inner join和delete inner join；Oracle delete join替代...
...> 0
and mw.size > 1;
下面是Oracle的：
Sql代码
DELETE TABLE1 where KHID exists ( select KHID from table2 where FWDWID=8)
Sql代码
DELETE TABLE1 where exists ( select 1 from table2 where and table1.khid=table2.khid and FWDWID=8);
Oracle的delete与join如何使用
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