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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...
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....
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.
...
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...
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...
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...
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...
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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What's the difference between VARCHAR and CHAR?
...CHAR(10),
Street VARCHAR(10));
Insert into temp
values('Pune','Oxford');
select length(city), length(street) from temp;
Output will be
length(City) Length(street)
10 6
Conclusion: To use storage space efficiently must use VARCHAR Instead CHAR if variable length is ...