大约有 1,954 项符合查询结果（耗时：0.0127秒） [XML]
Database development mistakes made by application developers [closed]
... exists--you should be using it.
It's quite common to see this failure on MySQL databases. I don't believe MyISAM supports it. InnoDB does. You'll find people who are using MyISAM or those that are using InnoDB but aren't using it anyway.
More here:
How important are constraints like NOT NULL...
SQL “select where not in subquery” returns no results
...LEFT JOIN / IS NULL: Oracle
NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL
There are three ways to do such a query:
LEFT JOIN / IS NULL:
SELECT *
FROM common
LEFT JOIN
table1 t1
ON t1.common_id = common.common_id
WHERE t1.common_id IS NULL
NOT EXISTS:
SELECT *
FROM...
What is the difference between HAVING and WHERE in SQL?
... Methinks you are quoting me out of context. The question was about mySQL's apparent deviation from the Standard, all but the last paragraph of my answer describes the Standard behaviour, and the last alludes to " the implicit GROUP BY clause mentioned in other answers." Are you saying your d...
SQL query for today's date minus two months
...
If you use MySQL this would become: MyDate < DATE_ADD(NOW(), INTERVAL -2 MONTH)
– Stefan
Feb 27 '14 at 15:51
...
How do I specify the Linq OrderBy argument dynamically?
...and 3.1 for me as well. with the error ~"cant translate". I use Pomelo for MySQl if that is relevant. The problem is the Expression. IF you hand code the expression it works. So instead of Lambda.Expression() just provide something like: LambdaExpression orderByExp1 = (Expression<Func<AgencyS...
How to get last inserted id?
...
I'm coming from a mysql background, I can't understand this command: Int32 newId = (Int32) myCommand.ExecuteScalar();
– Naguib Ihab
May 28 '15 at 1:23
...
How to change the output color of echo in Linux
...?
Anywhere that has a tty interpreter
xterm, gnome-terminal, kde-terminal, mysql-client-CLI and so on.
For example if you want to colorize your output with mysql you can use Perl
#!/usr/bin/perl -n
print "\033[1m\033[31m$1\033[36m$2\033[32m$3\033[33m$4\033[m" while /([|+-]+)|([0-9]+)|([a-zA-Z_]+)|([...
Does a UNIQUE constraint automatically create an INDEX on the field(s)?
...email, user_id) is enough, you don't need a separate index on email only - MySQL can use leftmost parts of a composite index. There may be some border cases where the size of an index can slow down your queries, but you should not worry about them until you actually run into them.
As for testing in...
Does Foreign Key improve query performance?
...
foreign keys do improve performance, at least in MySQL. Moreover, you're right, the creation of a FK does not create an index; the creation of a FK requires an index
– Félix Gagnon-Grenier
Aug 26 '14 at 17:31
...
Database Structure for Tree Data Structure
...
Have a look at Managing Hierarchical Data in MySQL. It discusses two approaches for storing and managing hierarchical (tree-like) data in a relational database.
The first approach is the adjacency list model, which is what you essentially describe: having a foreign key...