大约有 30,000 项符合查询结果（耗时：0.0249秒） [XML]
CHECK constraint in MySQL is not working
...GER `test_before_insert` BEFORE INSERT ON `Test`
FOR EACH ROW
BEGIN
IF CHAR_LENGTH( NEW.ID ) < 4 THEN
SIGNAL SQLSTATE '12345'
SET MESSAGE_TEXT := 'check constraint on Test.ID failed';
END IF;
END$$
DELIMITER ;
Prior to MySQL 5.5 you had to cause an error, e.g. ca...
Counting DISTINCT over multiple columns
... the columns, then get the distinct count of instances of the concatenated string.
SELECT count(DISTINCT concat(DocumentId, DocumentSessionId)) FROM DocumentOutputItems;
In MySQL you can do the same thing without the concatenation step as follows:
SELECT count(DISTINCT DocumentId, DocumentSessio...
Securely storing environment variables in GAE with app.yaml
...m google.appengine.ext import ndb
class Settings(ndb.Model):
name = ndb.StringProperty()
value = ndb.StringProperty()
@staticmethod
def get(name):
NOT_SET_VALUE = "NOT SET"
retval = Settings.query(Settings.name == name).get()
if not retval:
retval = Settings()
retva...
Non-Relational Database Design [closed]
...DBs are a massive win, and the drawbacks of less flexible queries and some extra code for data validation seems a small price to pay.
Have you hit your head against anything that seems impossible?
Not yet. Map/reduce as a means of querying a database is unfamiliar, and requires a lot more thinking...
List of Rails Model Types
...
:binary
:boolean
:date
:datetime
:decimal
:float
:integer
:primary_key
:string
:text
:time
:timestamp
These are documented under column in the Active Record API.
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How to insert a newline in front of a pattern?
...Linux and OS X:
sed 's/regexp/\'$'\n/g'
In general, for $ followed by a string literal in single quotes bash performs C-style backslash substitution, e.g. $'\t' is translated to a literal tab. Plus, sed wants your newline literal to be escaped with a backslash, hence the \ before $. And finally, ...
Strip whitespace from jsp output
...
Please, use the trim funcion, example
fn:trim(string1)
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How to concatenate string variables in Bash
In PHP, strings are concatenated together as follows:
30 Answers
30
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Why is there extra padding at the top of my UITableView with style UITableViewStyleGrouped in iOS7
...the contentInset.top dynamically as well. Having to remember to remove an extra 35px whenever I recalculate contentInset.top is tedious.
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Why not infer template parameter from constructor?
...nd operator=). So suppose you are using your class like this :
MyClass m(string s);
MyClass *pm;
*pm = m;
I am not sure if it would be so obvious for the parser to know what template type is the MyClass pm;
Not sure if what I said make sense but feel free to add some comment, that's an interest...