大约有 40,000 项符合查询结果（耗时：0.0244秒） [XML]
What's the difference between identifying and non-identifying relationships?
...
An identifying relationship is when the existence of a row in a child table depends on a row in a parent table. This may be confusing because it's common practice these days to create a pseudokey for a child table, but not make the foreign key to the parent part of the child's primary key. Fo...
Retrieve the maximum length of a VARCHAR column in SQL Server
I want to find the longest VARCHAR in a specific column of a SQL Server table.
10 Answers
...
What is the most ridiculous pessimization you've seen? [closed]
...
Databases are pessimization playland.
Favorites include:
Split a table into multiples (by date range, alphabetic range, etc.) because it's "too big".
Create an archive table for retired records, but continue to UNION it with the production table.
Duplicate entire databases by (division/cus...
Do I need to create indexes on foreign keys on Oracle?
I have a table A and a table B . A has a foreign key to B on B 's primary key, B_ID .
7 Answers
...
How can I find out what FOREIGN KEY constraint references a table in SQL Server?
I am trying to drop a table but getting the following message:
15 Answers
15
...
Find difference between timestamps in seconds in PostgreSQL
I have a table in PostgreSQL 8.3 with 2 timestamp columns. I would like to get the difference between these timestamps in seconds. Could you please help me how to get this done?
...
Vertically centering a div inside another div [duplicate]
...
tl;dr
Vertical align middle works, but you will have to use table-cell on your parent element and inline-block on the child.
This solution is not going to work in IE6 & 7. Yours is the safer way to go for those. But since you tagged your question with CSS3 and HTML5 I was thinkin...
Order data frame rows according to vector with specific order
...
Does anyone know a data.table version of this?
– Reilstein
Sep 23 '16 at 17:50
2
...
How to avoid mysql 'Deadlock found when trying to get lock; try restarting transaction'
I have a innoDB table which records online users. It gets updated on every page refresh by a user to keep track of which pages they are on and their last access date to the site. I then have a cron that runs every 15 minutes to DELETE old records.
...
How do I delete a fixed number of rows with sorting in PostgreSQL?
...
You could try using the ctid:
DELETE FROM logtable
WHERE ctid IN (
SELECT ctid
FROM logtable
ORDER BY timestamp
LIMIT 10
)
The ctid is:
The physical location of the row version within its table. Note that although the ctid can be used to locate the...