大约有 9,000 项符合查询结果（耗时：0.0313秒） [XML]
Why is SELECT * considered harmful?
...ich was which? SELECT * can also confuse views (at least in some versions SQL Server) when underlying table structures change -- the view is not rebuilt, and the data which comes back can be nonsense. And the worst part of it is that you can take care to name your columns whatever you want, but th...
How to verify if a file exists in a batch file?
...ndler echo Now Exiting && Exit
if not exist C:\myprogram\html\data.sql Exit
We will take those three files and put it in a temporary place. After deleting the folder, it will restore those three files.
xcopy "test" "C:\temp"
xcopy "test2" "C:\temp"
del C:\myprogram\sync\
xcopy "C:\temp" "...
Overriding a Rails default_scope
... like: def self.random; unscoped.order('rand()'); end unscoped removes ALL sql before it, not just what is listed under default_scope. While technically a correct answer, be careful using unstopped
– Schneems
Dec 25 '11 at 21:58
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Retrieving the last record in each group - MySQL
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MySQL 8.0 now supports windowing functions, like almost all popular SQL implementations. With this standard syntax, we can write greatest-n-per-group queries:
WITH ranked_messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTITIO...
In MySQL queries, why use join instead of where?
...d
From a Performance Perspective:
Where supported (Oracle 9i+, PostgreSQL 7.2+, MySQL 3.23+, SQL Server 2000+), there is no performance benefit to using either syntax over the other. The optimizer sees them as the same query. But more complex queries can benefit from using ANSI-92 syntax:
A...
Create a new database with MySQL Workbench
Being new to MySQL, I have installed the latest version of the MySQL Workbench (5.2.33). I would like to know how you can create a database with this application. In the Overview tab of the SQL editor there are few "MySQL Schema" displayed, are these schemas the existing databases?
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MySQL root password change
I have been trying to reset my MySQL root password. I have run the mysqld_safe --skip-grant-tables, updated the root password, and checked the user table to make sure it is there. Once restarting the mysql daemon I tried logging in with the new root password that I just set and still get Access de...
Altering a column: null to not null
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Its strange the MS SQL Management Studio does not allow that option, it brags about "Dropping table ..."
– Sebastian
May 2 '13 at 11:25
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Is there a query language for JSON?
Is there a (roughly) SQL or XQuery-like language for querying JSON?
22 Answers
22
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MySQL, update multiple tables with one query
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If I want to include "LIMIT" to the SQL Query, do I have to say LIMIT 1 or LIMIT 2?
– Bluedayz
Aug 25 '14 at 16:31
2
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