大约有 47,000 项符合查询结果（耗时：0.0235秒） [XML]
Random record from MongoDB
...llection.
db.mycoll.aggregate([{ $sample: { size: 1 } }])
If you want to select the random document(s) from a filtered subset of the collection, prepend a $match stage to the pipeline:
// Get one random document matching {a: 10} from the mycoll collection.
db.mycoll.aggregate([
{ $match: { a:...
Insert, on duplicate update in PostgreSQL?
...try the UPDATE again
END;
END LOOP;
END;
$$
LANGUAGE plpgsql;
SELECT merge_db(1, 'david');
SELECT merge_db(1, 'dennis');
There's possibly an example of how to do this in bulk, using CTEs in 9.1 and above, in the hackers mailing list:
WITH foos AS (SELECT (UNNEST(%foo[])).*)
updated...
How to add column if not exists on PostgreSQL?
...s, _col text, _type regtype)
RETURNS bool AS
$func$
BEGIN
IF EXISTS (SELECT 1 FROM pg_attribute
WHERE attrelid = _tbl
AND attname = _col
AND NOT attisdropped) THEN
RETURN FALSE;
ELSE
EXECUTE format('ALTER TABLE %s ADD COLUMN %I %s...
Convert string[] to int[] in one line of code using LINQ
...you would need the extra ToArray call to get an array:
int[] myInts = arr.Select(int.Parse).ToArray();
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CASCADE DELETE just once
...you want to cascade.
DELETE FROM some_child_table WHERE some_fk_field IN (SELECT some_id FROM some_Table);
DELETE FROM some_table;
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How do you kill all current connections to a SQL Server 2005 database?
...problems ALTER DATABASE aspnetdb SET SINGLE_USER WITH ROLLBACK IMMEDIATE select GETDATE() ALTER DATABASE aspnetdb SET MULTI_USER what do you have instead of the commented out code?
– SQLMenace
Aug 17 '10 at 18:33
...
How can I use optional parameters in a T-SQL stored procedure?
...ame varchar(25) = null,
@Title varchar(25) = null
AS
BEGIN
SELECT ID, FirstName, LastName, Title
FROM tblUsers
WHERE
(@FirstName IS NULL OR (FirstName = @FirstName))
AND (@LastName IS NULL OR (LastName = @LastName ))
AND (@Tit...
How to export table as CSV with headings on Postgresql?
...
@arilwan psql -c "\COPY (SELECT * FROM mytable) TO STDOUT" > mytable.csv
– Juha Palomäki
Jun 6 '19 at 16:00
...
Select distinct using linq [duplicate]
...
myList.GroupBy(test => test.id)
.Select(grp => grp.First());
Edit: as getting this IEnumerable<> into a List<> seems to be a mystery to many people, you can simply write:
var result = myList.GroupBy(test => test.id)
.S...
How to check if field is null or empty in MySQL?
...
Either use
SELECT IF(field1 IS NULL or field1 = '', 'empty', field1) as field1
from tablename
or
SELECT case when field1 IS NULL or field1 = ''
then 'empty'
else field1
end as field1
from tablename
...