大约有 45,000 项符合查询结果（耗时：0.0293秒） [XML]
extract part of a string using bash/cut/split
...gs based on position using numbers:
${MYVAR:3} # Remove the first three chars (leaving 4..end)
${MYVAR::3} # Return the first three characters
${MYVAR:3:5} # The next five characters after removing the first 3 (chars 4-9)
You can also replace particular strings or patterns using:
${MYVAR/sear...
Understanding the meaning of the term and the concept - RAII (Resource Acquisition is Initialization
...class FileHandle
{
FILE* file;
public:
explicit FileHandle(const char* name)
{
file = fopen(name);
if (!file)
{
throw "MAYDAY! MAYDAY";
}
}
~FileHandle()
{
// The only reason we are checking the file pointer for validity
...
Should I use static_cast or reinterpret_cast when casting a void* to whatever
...g between pointer types (as is fairly common when indexing in memory via a char*, for example), static_cast will generate a compiler error and you'll be forced to use reinterpret_cast anyway.
In practice I use reinterpret_cast because it's more descriptive of the intent of the cast operation. You c...
Simple way to transpose columns and rows in SQL?
...3, 5),
('Blue', 2, 2, 9, 1);
Union All, Aggregate and CASE Version:
select name,
sum(case when color = 'Red' then value else 0 end) Red,
sum(case when color = 'Green' then value else 0 end) Green,
sum(case when color = 'Blue' then value else 0 end) Blue
from
(
select color, Paul value...
Delete all data in SQL Server database
...stem stored procs */
DECLARE @name VARCHAR(128)
DECLARE @SQL VARCHAR(254)
SELECT @name = (SELECT TOP 1 [name] FROM sysobjects WHERE [type] = 'P' AND category = 0 ORDER BY [name])
WHILE @name is not null
BEGIN
SELECT @SQL = 'DROP PROCEDURE [dbo].[' + RTRIM(@name) +']'
EXEC (@SQL)
PRINT ...
postgresql: INSERT INTO … (SELECT * …)
...ostgres
CREATE TABLE tblA (id serial, time integer);
INSERT INTO tblA
SELECT id, time
FROM dblink('dbname=dbtest', 'SELECT id, time FROM tblB')
AS t(id integer, time integer)
WHERE time > 1000;
TABLE tblA;
id | time
----+------
1 | 5000
2 | 2000
(2 rows)
PostgreSQL has ...
What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN? [duplicate]
...These pictures don't do it for me. Why is the top right picture not simply SELECT * FROM TableA;? Why is the top left picture not simply SELECT * FROM TableB;? Why is the top middle picture not SELECT * FROM A INTERSECT SELECT * FROM B ? etc
– onedaywhen
Sep 9 ...
Optimal way to concatenate/aggregate strings
...Transact SQL, which should work fine in Azure.
;WITH Partitioned AS
(
SELECT
ID,
Name,
ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Name) AS NameNumber,
COUNT(*) OVER (PARTITION BY ID) AS NameCount
FROM dbo.SourceTable
),
Concatenated AS
(
SELECT
...
PostgreSQL function for last inserted ID
...e:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John');
SELECT currval('persons_id_seq');
The name of the sequence must be known, it's really arbitrary; in this example we assume that the table persons has an id column created with the SERIAL pseudo-type. To avoid relying on thi...
T-SQL: Deleting all duplicate rows but keeping one [duplicate]
... I do not care about that. I still need to keep one of these rows however. SELECT DISTINCT won't work because it operates on all columns and I need to suppress duplicates based on the key columns.
...