大约有 7,000 项符合查询结果（耗时：0.0211秒） [XML]
Tactics for using PHP in a high-load site
...l you measure and compare your changes.
For example, for many years, the MySQL query cache was the solution to all of our performance problems. If your site was slow, MySQL experts suggested turning the query cache on. It turns out that if you have a high write load, the cache is actually cripplin...
Does MySQL ignore null values on unique constraints?
...
Yes, MySQL allows multiple NULLs in a column with a unique constraint.
CREATE TABLE table1 (x INT NULL UNIQUE);
INSERT table1 VALUES (1);
INSERT table1 VALUES (1); -- Duplicate entry '1' for key 'x'
INSERT table1 VALUES (NULL);...
#1071 - Specified key was too long; max key length is 1000 bytes
...The INT(1) and INT(32) data types indicates another misunderstanding about MySQL. The numeric argument has no effect related to storage or the range of values allowed for the column. INT is always 4 bytes, and it always allows values from -2147483648 to 2147483647. The numeric argument is about p...
How do I check if a column is empty or null in MySQL?
...OR some_col = ' ' (one space inserted in the string) then it works on both MySQL and Oracle, see answer of "onedaywhen". some_col = '' doesn't work on Oracle as empty strings mean NULL there.
– Johanna
May 18 '15 at 14:07
...
In MySQL, how to copy the content of one table to another table within the same database?
I am new to MySQL. I would like to copy the content of one table to another table within the same database. Basically, I would like to insert to a table from another table. Is there easy way of doing this?
...
How do I show the schema of a table in a MySQL database?
From the MySQL console, what command displays the schema of any given table?
5 Answers
...
How to delete from multiple tables in MySQL?
...h out to an EXISTS in 99% of the cases and then there is the 1% where this MySQL syntax takes the day.
share
|
improve this answer
|
follow
|
...
MySQL ON vs USING?
In a MySQL JOIN , what is the difference between ON and USING() ? As far as I can tell, USING() is just more convenient syntax, whereas ON allows a little more flexibility when the column names are not identical. However, that difference is so minor, you'd think they'd just do away with USI...
What's the difference between VARCHAR and CHAR?
What's the difference between VARCHAR and CHAR in MySQL?
14 Answers
14
...
How to declare a variable in MySQL?
How to declare a variable in mysql, so that my second query can use it?
7 Answers
7
...