大约有 47,000 项符合查询结果（耗时：0.0494秒） [XML]
How to 'insert if not exists' in MySQL?
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Solution:
INSERT INTO `table` (`value1`, `value2`)
SELECT 'stuff for value1', 'stuff for value2' FROM DUAL
WHERE NOT EXISTS (SELECT * FROM `table`
WHERE `value1`='stuff for value1' AND `value2`='stuff for value2' LIMIT 1)
Explanation:
The innermost query
SELECT *...
LINQ's Distinct() on a particular property
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(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
HashSet<TKey> seenKeys = new HashSet<TKey>();
foreach (TSource element in source)
{
if (seenKeys.Add(keySelector(element)))
{
yield return element;
}
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No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK?
...and check your installed JREs. You should have an entry with a JDK there.
Select the Execution Env as show below. Click OK
Then Right-Click on your Project -> Maven -> Update Project
Additionally, you may have to change Maven JRE (see @jlars62 answer) which is as follows. Goto Run -> Ru...
How to automatically navigate to the current class in Intellij Idea Project Tool Window?
...expands to show the currently open class (or file), and this class becomes selected in the tree.
6 Answers
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Reliable method to get machine's MAC address in C#
...aces()
where nic.OperationalStatus == OperationalStatus.Up
select nic.GetPhysicalAddress().ToString()
).FirstOrDefault();
Or:
String firstMacAddress = NetworkInterface
.GetAllNetworkInterfaces()
.Where( nic => nic.OperationalStatus == OperationalStatus.Up &&...
Can you force Visual Studio to always run as an Administrator in Windows 8?
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In Windows 8 & 10, you have to right-click devenv.exe and select "Troubleshoot compatibility".
Select "Troubleshoot program"
Check "The program requires additional permissions"
Click "Next"
Click "Test the program..."
Wait for the program to launch
Click "Next"
Select "Yes, save...
MySQL SELECT WHERE datetime matches day (and not necessarily time)
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NEVER EVER use a selector like DATE(datecolumns) = '2012-12-24' - it is a performance killer:
it will calculate DATE() for all rows, including those, that don't match
it will make it impossible to use an index for the query
It is much fas...
How to for each the hashmap? [duplicate]
...I did too, in case it helps someone else :
HashMap<String, HashMap> selects = new HashMap<String, HashMap>();
for(Map.Entry<String, HashMap> entry : selects.entrySet()) {
String key = entry.getKey();
HashMap value = entry.getValue();
// do what you have to do here
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SQL Server Profiler - How to filter trace to only display events from one database?
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Under Trace properties > Events Selection tab > select show all columns. Now under column filters, you should see the database name. Enter the database name for the Like section and you should see traces only for that database.
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Eclipse does not highlight matching variables
...y:
window > preferences > java > editor > mark occurrences
Select all options available there.
Also go to:
Preferences > General > Editors > Text Editors > Annotations
Compare the settings for 'Occurrences' and 'Write Occurrences'
Make sure that you don't have the 'T...