大约有 40,000 项符合查询结果（耗时：0.0208秒） [XML]
Why is the gets function so dangerous that it should not be used?
...deal would have been to have a "string pointer" identify a byte that would select among a few different string/buffer/buffer-info formats, with one value of prefix byte indicating a struct that contained the prefix byte [plus padding], plus the buffer size, used size, and address of the actual text....
Postgres: INSERT if does not exist already
...onditional INSERT in PostgreSQL:
INSERT INTO example_table
(id, name)
SELECT 1, 'John'
WHERE
NOT EXISTS (
SELECT id FROM example_table WHERE id = 1
);
CAVEAT This approach is not 100% reliable for concurrent write operations, though. There is a very tiny race condition between...
What is the best collation to use for MySQL with PHP? [closed]
...ng utf8_general_ci.
MySQL will not distinguish between some characters in select statements, if the utf8_general_ci collation is used. This can lead to very nasty bugs - especially for example, where usernames are involved. Depending on the implementation that uses the database tables, this problem...
Best way to check for “empty or null value”
... '
Demo
Empty string equals any string of spaces when cast to char(n):
SELECT ''::char(5) = ''::char(5) AS eq1
, ''::char(5) = ' '::char(5) AS eq2
, ''::char(5) = ' '::char(5) AS eq3;
Result:
eq1 | eq2 | eq3
----+-----+----
t | t | t
Test for "null or empty string" w...
Comparing date ranges
... range_start, here's some simple SQL to retrieve all the matching rows:
SELECT *
FROM periods
WHERE NOT (range_start > @check_period_end
OR range_end < @check_period_start)
Note the NOT in there. Since the two simple rules finds all the non-matching rows, a simple NOT will reve...
Should I add .vcxproj.filter files to source control?
...st found that if you use Git you can mark .filter files to be treated as a union for merging to make it simpler. Just add the line:
*.vcxproj.filters merge=union
to your .gitattributes file.
See Using .gitattributes to avoid merge conflicts for more details.
...
SQL: deleting tables with prefix
...r you:
In the MySQL shell or through PHPMyAdmin, use the following query
SELECT CONCAT( 'DROP TABLE ', GROUP_CONCAT(table_name) , ';' )
AS statement FROM information_schema.tables
WHERE table_name LIKE 'myprefix_%';
This will generate a DROP statement which you can than copy and execut...
Compare two List objects for equality, ignoring order [duplicate]
...here duplicates in either are ignored), you can use:
// check that [(A-B) Union (B-A)] is empty
var areEquivalent = !list1.Except(list2).Union( list2.Except(list1) ).Any();
Using the set operations (Intersect, Union, Except) is more efficient than using methods like Contains. In my opinion, it al...
How to convert int to char with leading zeros?
...
Try this: select right('00000' + cast(Your_Field as varchar(5)), 5)
It will get the result in 5 digits, ex: 00001,...., 01234
share
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Why would someone use WHERE 1=1 AND in a SQL clause?
...mple code to Greg's answer:
dim sqlstmt as new StringBuilder
sqlstmt.add("SELECT * FROM Products")
sqlstmt.add(" WHERE 1=1")
''// From now on you don't have to worry if you must
''// append AND or WHERE because you know the WHERE is there
If ProductCategoryID <> 0 then
sqlstmt.AppendForm...