大约有 44,000 项符合查询结果（耗时：0.0253秒） [XML]
How to select rows with no matching entry in another table?
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Here's a simple query:
SELECT t1.ID
FROM Table1 t1
LEFT JOIN Table2 t2 ON t1.ID = t2.ID
WHERE t2.ID IS NULL
The key points are:
LEFT JOIN is used; this will return ALL rows from Table1, regardless of whether or not there is a matching row i...
PostgreSQL - fetch the row which has the Max value for a column
...sted index lookup into lives - on my machine
-- the latter query plan was selected given my memory settings and
-- histogram
SELECT
l1.*
FROM
lives AS l1
INNER JOIN (
SELECT
usr_id,
MAX(time_stamp) AS time_stamp_max
FROM
lives
GROUP BY
usr_id
) AS l2
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How to drive C#, C++ or Java compiler to compute 1+2+3+…+1000 at compile time?
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C# example to error at compile time.
class Foo
{
const char Sum = (1000 + 1) * 1000 / 2;
}
Produces the following compilation error:
Constant value '500500' cannot be converted to a 'char'
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Rails select helper - Default selected value, how?
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This should do it:
<%= f.select :project_id, @project_select, :selected => params[:pid] %>
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Linq code to select one item
I find myself writing a lot of code like this to select one item that matches
7 Answers
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Rails 3: Get Random Record
...You can use the following trick on an indexed column (PostgreSQL syntax):
select *
from my_table
where id >= trunc(
random() * (select max(id) from my_table) + 1
)
order by id
limit 1;
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What is the max size of localStorage values?
... Doesn't crash Chrome anymore... Interesting point: 5MB equals 2.5 Million chars on Chrome. So apparently, UFT16 is used for localStore.
– Felix Alcala
Sep 3 '11 at 17:10
1
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When should I use nil and NULL in Objective-C?
...ke a C pointer) in Objective-C. Like nil , NULL got no value nor address.
char *myChar = NULL;
struct MyStruct *dStruct = NULL;
So if there is a situation, when I need to check my struct (structure type variable) is empty or not then, I will use:
if (dStruct == NULL)
NSLog("The struct is emp...
How to copy a row and insert in same table with a autoincrement field in MySQL?
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Use INSERT ... SELECT:
insert into your_table (c1, c2, ...)
select c1, c2, ...
from your_table
where id = 1
where c1, c2, ... are all the columns except id. If you want to explicitly insert with an id of 2 then include that in your INSER...
How to select a drop-down menu value with Selenium using Python?
I need to select an element from a drop-down menu.
13 Answers
13
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