大约有 40,000 项符合查询结果（耗时：0.0440秒） [XML]
COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better? [duplicate]
...for all your queries that need to count everything, even for joins, use *
SELECT boss.boss_id, COUNT(subordinate.*)
FROM boss
LEFT JOIN subordinate on subordinate.boss_id = boss.boss_id
GROUP BY boss.id
But don't use COUNT(*) for LEFT joins, as that will return 1 even if the subordinate table doe...
Reason for Column is invalid in the select list because it is not contained in either an aggregate f
...c
1 def
1 ghi
2 jkl
2 mno
2 pqr
And I do the following query:
SELECT a, b
FROM T
GROUP BY a
The output should have two rows, one row where a=1 and a second row where a=2.
But what should the value of b show on each of these two rows? There are three possibilities in each case, and no...
How to get Url Hash (#) from server side
...hash again) and/or perform other actions.
We used jQuery to simplify the selecting of the field, etc ... all in all it ends up being a few jQuery calls, one to save the value, and another to restore it.
Before submit:
$("form").submit(function() {
$("input", "#urlhash").val(window.location.has...
Mark parameters as NOT nullable in C#/.NET?
... where o.Value == null
select o;
bool paramsNull = nullParams.Count() > 0;
if (paramsNull)
{
StringBuilder sb = new StringBuilder();
foreach (var param in nullParams)
...
File Explorer in Android Studio
...en robot icon on the toolbar, to the left of the help icon). From the ADM, select the device/emulator, then select the File Explorer tab.
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How to request a random row in SQL?
...
See this post: SQL to Select a random row from a database table. It goes through methods for doing this in MySQL, PostgreSQL, Microsoft SQL Server, IBM DB2 and Oracle (the following is copied from that link):
Select a random row with MySQL:
SELE...
How to select date from datetime column?
...ry.
Use BETWEEN or >, <, = operators which allow to use an index:
SELECT * FROM data
WHERE datetime BETWEEN '2009-10-20 00:00:00' AND '2009-10-20 23:59:59'
Update: the impact on using LIKE instead of operators in an indexed column is high. These are some test results on a table with 1,...
How do I style a dropdown with only CSS?
Is there a CSS-only way to style a <select> dropdown?
24 Answers
24
...
Why does this async action hang?
...DBConnection.ExecuteAsync<ResultClass>(
ds => ds.Execute("select slow running data into result"));
}
What's the difference? There's now no awaiting anywhere, so nothing being implicitly scheduled to the UI thread. For simple methods like these that have a single return, there's no...
Can an int be null in Java?
... primitive types,we have fixed memory size i.e for int we have 4 bytes and char we have 2 bytes. And null is used only for objects because there memory size is not fixed.
So by default we have,
int a=0;
and not
int a=null;
Same with other primitive types and hence null is only used for...