大约有 43,000 项符合查询结果（耗时：0.0323秒） [XML]
Use 'class' or 'typename' for template parameters? [duplicate]
...s expected T will always be a class, with "typename" if other types (int, char* whatever) may be expected. Consider it a usage hint.
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How do I query if a database schema exists
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Are you looking for sys.schemas?
IF NOT EXISTS (SELECT * FROM sys.schemas WHERE name = 'jim')
BEGIN
EXEC('CREATE SCHEMA jim')
END
Note that the CREATE SCHEMA must be run in its own batch (per the answer below)
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Detect if value is number in MySQL
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This should work in most cases.
SELECT * FROM myTable WHERE concat('',col1 * 1) = col1
It doesn't work for non-standard numbers like
1e4
1.2e5
123. (trailing decimal)
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Best way to create enum of strings?
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@Mark, true, it can't handle any character. If the OP just wants a single char, this solution is more straight forward than The Elite Gentleman suggestion. But indeed: if the range of characters exceeds the ones a valid Java identifier can have, this is a no...
Find rows that have the same value on a column in MySQL
...sses and how many times they're used, with the most used addresses first.
SELECT email,
count(*) AS c
FROM TABLE
GROUP BY email
HAVING c > 1
ORDER BY c DESC
If you want the full rows:
select * from table where email in (
select email from table
group by email having count(*) &g...
How do I run Visual Studio as an administrator by default?
...indows 8, 8.1 and 10
In Windows 8, 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 ...
Removing duplicate rows from table in Oracle
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Use the rowid pseudocolumn.
DELETE FROM your_table
WHERE rowid not in
(SELECT MIN(rowid)
FROM your_table
GROUP BY column1, column2, column3);
Where column1, column2, and column3 make up the identifying key for each record. You might list all your columns.
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What is the error “Every derived table must have its own alias” in MySQL?
...er), which can the be used to refer to it in the rest of the outer query.
SELECT ID FROM (
SELECT ID, msisdn FROM (
SELECT * FROM TT2
) AS T
) AS T
In your case, of course, the entire query could be replaced with:
SELECT ID FROM TT2
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SQL Server loop - how do I loop through a set of records
how do I loop through a set of records from a select?
8 Answers
8
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selecting unique values from a column
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Use the DISTINCT operator in MySQL:
SELECT DISTINCT(Date) AS Date FROM buy ORDER BY Date DESC;
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