大约有 31,500 项符合查询结果（耗时：0.0181秒） [XML]
How to declare a type as nullable in TypeScript?
...wever, salary = undefined; will work just fine in this case. Solution: use Union i.e. '|'
– Ankur Nigam
Apr 21 at 6:19
...
When should I use cross apply over inner join?
... master
),
t AS
(
SELECT 1 AS id
UNION ALL
SELECT 2
)
SELECT *
FROM t
JOIN q
ON q.rn <= t.id
runs for almost 30 seconds, while this one:
WITH t AS
(
SELECT 1 AS id
UNION ALL
SELECT 2
...
Difference between CTE and SubQuery?
... most useful for recursion:
WITH hier(cnt) AS (
SELECT 1
UNION ALL
SELECT cnt + 1
FROM hier
WHERE cnt < @n
)
SELECT cnt
FROM hier
will return @n rows (up to 101). Useful for calendars, dummy rowsets etc.
They are also more readable (i...
How does HashSet compare elements for equality?
...ploye() { Name = "Rob" });
Display(hashSetB);
var union = hashSet.Union<Employe>(hashSetB).ToList();
Display(union);
var inter = hashSet.Intersect<Employe>(hashSetB).ToList();
Display(inter);
var except = hashSet.Ex...
Best way to select random rows PostgreSQL
...ner
) r
JOIN big b USING (id) -- eliminate miss
UNION -- eliminate dupe
SELECT b.*
FROM (
SELECT 1 + trunc(random() * 5100000)::int AS id
FROM random_pick r -- plus 3 percent - adapt to your needs
LIMIT ...
What is the most efficient/elegant way to parse a flat table into a tree?
...RECURSIVE MyTree AS (
SELECT * FROM MyTable WHERE ParentId IS NULL
UNION ALL
SELECT m.* FROM MyTABLE AS m JOIN MyTree AS t ON m.ParentId = t.Id
)
SELECT * FROM MyTree;
I tested recursive queries in MySQL 8.0 in my presentation Recursive Query Throwdown in 2017.
Below is my original an...
Is String.Format as efficient as StringBuilder
...var referToTheComputedValuesSoCompilerCantOptimiseTheLoopsAway= concatkeys.Union(stringbuilderkeys).Union(cachedsbkeys).Union(formatkeys).LastOrDefault(x=>x[1]=='-');
Console.WriteLine(referToTheComputedValuesSoCompilerCantOptimiseTheLoopsAway);
...
What guarantees are there on the run-time complexity (Big-O) of LINQ methods?
...).
Distinct, GroupBy Join, and I believe also the set-aggregation methods (Union, Intersect and Except) use hashing, so they should be close to O(N) instead of O(N²).
Contains checks for an ICollection implementation, so it may be O(1) if the underlying collection is also O(1), such as a HashSet<...
Split function equivalent in T-SQL?
...1,12,13,14,15'
SET @delimiter = ','
;WITH cte AS
(
SELECT 0 a, 1 b
UNION ALL
SELECT b, CHARINDEX(@delimiter, @str, b) + LEN(@delimiter)
FROM CTE
WHERE b > a
)
SELECT SUBSTRING(@str, a,
CASE WHEN b > LEN(@delimiter)
THEN b - a - LEN(@delimiter)
ELSE LEN(@str) - a +...
How to output MySQL query results in CSV format?
...u can include header by prepending "SELECT 'order_id','product_name','qty' UNION" before the real query. First select query returns header, second query returns real data; UNION joins it together.
– petrkotek
Jun 14 '13 at 4:35
...