大约有 40,000 项符合查询结果（耗时：0.0294秒） [XML]
How do I get the MAX row with a GROUP BY in LINQ query?
...t by t.SerialNumber
into g
select new
{
SerialNumber = g.Key,
uid = (from t2 in g select t2.uid).Max()
};
}
...
Is there a way to access the “previous row” value in a SELECT statement?
...d to order by some column for this to be meaningful. Something like this:
select t1.value - t2.value from table t1, table t2
where t1.primaryKey = t2.primaryKey - 1
If you know how to order things but not how to get the previous value given the current one (EG, you want to order alphabetically) ...
Selecting the last value of a column
...
Another good resource is the selected answer at productforums.google.com/forum/#!topic/docs/p3t3feg7Jic which shows how to get the first, last, or nth row in a FILTER()ed range, similar to @Geta's answer.
– Aaron Blenkush
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How to check if a column exists in a SQL Server table?
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SQL Server 2005 onwards:
IF EXISTS(SELECT 1 FROM sys.columns
WHERE Name = N'columnName'
AND Object_ID = Object_ID(N'schemaName.tableName'))
BEGIN
-- Column Exists
END
Martin Smith's version is shorter:
IF COL_LENGTH('schemaName.tabl...
mysql -> insert into tbl (select from another table) and some default values [duplicate]
As the title says, I am trying to insert into one table selecting values from another table and some default values.
5 Ans...
Not equal != operator on NULL
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As a manual workaround, you could commonly SELECT * FROM MyTable WHERE coalesce(MyColumn, 'x') <> 'x' to assign a constant if it is NULL value, providing you give an appropriate datatype for the sentinel value x (in this case a string/char). This is TSQL syntax ...
How to use greater than operator with date?
..._date with single quote causing it to become string, use backtick instead
SELECT * FROM `la_schedule` WHERE `start_date` > '2012-11-18';
SQLFiddle Demo
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Is there any performance gain in indexing a boolean field?
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It depends on the actual queries and the selectivity of the index/query combination.
Case A: condition WHERE isok = 1 and nothing else there:
SELECT *
FROM tableX
WHERE isok = 1
If the index is selective enough (say you have 1M rows and only 1k have isok = 1), ...
How to convert timestamp to datetime in MySQL?
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SELECT from_unixtime( TIMESTAMP( "2011-12-01", "22:01:23.048" ) ) doesn't work. why? using v5.6
– Janus Troelsen
Feb 4 '14 at 18:44
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SQL: How to perform string does not equal
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Try the following query
select * from table
where NOT (tester = 'username')
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