大约有 6,100 项符合查询结果（耗时：0.0160秒） [XML]
Which SQL query is faster? Filter on Join criteria or Where clause?
...LEFT JOIN.
In your very case this will look like this:
SELECT *
FROM TableA a
LEFT JOIN
TableXRef x
ON x.TableAID = a.ID
AND a.ID = 1
LEFT JOIN
TableB b
ON x.TableBID = b.ID
or this:
SELECT *
FROM TableA a
LEFT JOIN
TableXRef x
ON x.TableAI...
selecting unique values from a column
I have a MySQL table which contains the following type of information:
9 Answers
9
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SQL Server: Maximum character length of object names
...
Yes, it is 128, except for temp tables, whose names can only be up to 116 character long.
It is perfectly explained here.
And the verification can be easily made with the following script contained in the blog post before:
DECLARE @i NVARCHAR(800)
SELECT ...
Export and Import all MySQL databases at one time
...-databases > alldb.sql
mysqldump -u root -p --all-databases --skip-lock-tables > alldb.sql
Import:
mysql -u root -p < alldb.sql
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Delete/Reset all entries in Core Data?
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You can delete the SQLite file - but I choose to do it by purging the tables individually with a functions:
- (void) deleteAllObjects: (NSString *) entityDescription {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription enti...
Performance of FOR vs FOREACH in PHP
..._arr1 = array();
$test_arr2 = array();
$test_arr3 = array();
// hash tables
$test_arr4 = array();
$test_arr5 = array();
for ($i = 0; $i < $test_arr_size; ++$i)
{
mt_srand();
$hash = md5(mt_rand());
$key = substr($hash, 0, 5).$i;
$test_arr1[$i] = $test_arr2[$i] = $t...
How can I prevent the scrollbar overlaying content in IE10?
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This issue is also happening with Datatables on Bootstrap 4. Mi solution was:
Checked if the ie browser is opening.
Replaced table-responsive class for table-responsive-ie class.
CSS:
.table-responsive-ie {
display: block;
width: 100%;
overflow-x: auto;}
...
Which rows are returned when using LIMIT with OFFSET in MySQL?
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OFFSET is nothing but a keyword to indicate starting cursor in table
SELECT column FROM table LIMIT 18 OFFSET 8 -- fetch 18 records, begin with record 9 (OFFSET 8)
you would get the same result form
SELECT column FROM table LIMIT 8, 18
visual representation (R is one record in the ...
How can i query for null values in entity framework?
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Workaround for Linq-to-SQL:
var result = from entry in table
where entry.something.Equals(value)
select entry;
Workaround for Linq-to-Entities (ouch!):
var result = from entry in table
where (value == null ? entry.something == null : entr...
Pandas count(distinct) equivalent
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I believe this is what you want:
table.groupby('YEARMONTH').CLIENTCODE.nunique()
Example:
In [2]: table
Out[2]:
CLIENTCODE YEARMONTH
0 1 201301
1 1 201301
2 2 201301
3 1 201302
4 2 ...