大约有 44,000 项符合查询结果（耗时：0.0507秒） [XML]
The static keyword and its various uses in C++
... do different things. For instance, you could put a static void log(const char*) {} in each cpp file, and they could each all log in a different way.
share
|
improve this answer
|
...
COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better? [duplicate]
...for all your queries that need to count everything, even for joins, use *
SELECT boss.boss_id, COUNT(subordinate.*)
FROM boss
LEFT JOIN subordinate on subordinate.boss_id = boss.boss_id
GROUP BY boss.id
But don't use COUNT(*) for LEFT joins, as that will return 1 even if the subordinate table doe...
Is a Java string really immutable?
.... However, looking at the source code of String, we can see that the value character array for a substring is actually copied (using Arrays.copyOfRange(..)). This is why it goes unchanged.
You can install a SecurityManager, to avoid malicious code to do such things. But keep in mind that some libra...
How to select a single field for all documents in a MongoDB collection?
...nt such as:
db.student.find({}, {roll:1, _id:0})
The above statement will select all documents in the students collection, and the returned document will return only the roll field (and exclude the _id).
If we don't mention _id:0 the fields returned will be roll and _id. The '_id' field is always d...
Select first row in each GROUP BY group?
As the title suggests, I'd like to select the first row of each set of rows grouped with a GROUP BY .
17 Answers
...
How to un-escape a backslash-escaped string?
...WARNING: value.encode('utf-8').decode('unicode_escape') corrupts non-ASCII characters in the string. Unless the input is guaranteed to only contain ASCII characters, this is not a valid solution.
– Alex Peters
Jun 9 '19 at 11:46
...
Define variable to use with IN operator (T-SQL)
... VALUES (2)
INSERT INTO @MyList VALUES (3)
INSERT INTO @MyList VALUES (4)
SELECT *
FROM MyTable
WHERE MyColumn IN (SELECT Value FROM @MyList)
share
|
improve this answer
|
...
How to create a MySQL hierarchical recursive query
... or self-joins.
MySQL 8+
with recursive cte (id, name, parent_id) as (
select id,
name,
parent_id
from products
where parent_id = 19
union all
select p.id,
p.name,
p.parent_id
from products p
inner join cte
...
Left-pad printf with spaces
...
If you want the word "Hello" to print in a column that's 40 characters wide, with spaces padding the left, use the following.
char *ptr = "Hello";
printf("%40s\n", ptr);
That will give you 35 spaces, then the word "Hello". This is how you format stuff when you know how wide you wa...
How do I select an entire row which has the largest ID in the table?
...
You could use a subselect:
SELECT row
FROM table
WHERE id=(
SELECT max(id) FROM table
)
Note that if the value of max(id) is not unique, multiple rows are returned.
If you only want one such row, use @MichaelMior's answer,
SELEC...