大约有 40,000 项符合查询结果（耗时：0.0407秒） [XML]
Count number of rows within each group
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An old question without a data.table solution. So here goes...
Using .N
library(data.table)
DT <- data.table(df)
DT[, .N, by = list(year, month)]
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How to vertical align an inline-block in a line of text?
...nline-block that will take on some unknown width and height. (It'll have a table inside it with content dynamically generated). Further, the inline-block should be placed inside a line of text, such as "my text (BLOCK HERE)". To make it look pretty, I'm trying to make the block be vertically cent...
Is it correct to use DIV inside FORM?
...l. You can try it yourself at a HTML validator. Besides, it is almost inevitable these days, since the modern pages are build on div's. If it was not allowed, a simple wrapper or placing the form in a container would already make the page invalid.
– Nrzonline
S...
“Keep Me Logged In” - the best approach
...in, generate a large (128 to 256 bit) random token. Add that to a database table which maps the token to the userid, and then send it to the client in the cookie.
What if the attacker guesses the random token of another user?
Well, let's do some math here. We're generating a 128 bit random token....
How to concatenate columns in a Postgres SELECT?
I have two string columns a and b in a table foo .
8 Answers
8
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Where are my postgres *.conf files?
... # analyze
#autovacuum_vacuum_scale_factor = 0.2 # fraction of table size before vacuum
#autovacuum_analyze_scale_factor = 0.1 # fraction of table size before analyze
#autovacuum_freeze_max_age = 200000000 # maximum XID age before forced vacuum
# (change requires re...
How do you use script variables in psql?
...nd can then be substituted, for example, as ...
SELECT * FROM :myvariable.table1;
... or ...
SELECT * FROM table1 WHERE :myvariable IS NULL;
edit: As of psql 9.1, variables can be expanded in quotes as in:
\set myvariable value
SELECT * FROM table1 WHERE column1 = :'myvariable';
In olde...
Can I create a named default constraint in an add column statement in SQL Server?
In SQL Server, I have a new column on a table:
4 Answers
4
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Entity Framework and SQL Server View
...s solving performance issues using Tillito solution. Lets say you have the table:
Create table OrderDetail
(
Id int primary key,
CustomerId int references Customer(Id),
Amount decimal default(0)
);
Create index ix_customer on OrderDetail(CustomerId);
and your view...
Return rows in random order [duplicate]
Is it possible to write SQL query that returns table rows in random order every time the query run?
6 Answers
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