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When and why are database joins expensive?
...x strategy is available to the optimiser.
I used to be smarter than the MSSQL optimiser. That changed two versions ago. Now it generally teaches me. It is, in a very real sense, an expert system, codifying all the wisdom of many very clever people in a domain sufficiently closed that a rule-based s...
Sqlite primary key on multiple columns
What is the syntax for specifying a primary key on more than 1 column in SQLITE ?
9 Answers
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ActiveRecord: List columns in table from console
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If you are comfortable with SQL commands, you can enter your app's folder and run rails db, which is a brief form of rails dbconsole. It will enter the shell of your database, whether it is sqlite or mysql.
Then, you can query the table columns using...
ALTER TABLE to add a composite primary key
...table you will get an error when trying to drop it. In some versions of mysql the error message there was malformed (as of 5.5.17, this error message is still
alter table parent drop column id;
ERROR 1025 (HY000): Error on rename of
'./test/#sql-a04_b' to './test/parent' (errno: 150).
If you wa...
Querying data by joining two tables in two database on different servers
...ID
Once the link is established, you can also use OPENQUERY to execute a SQL statement on the remote server and transfer only the data back to you. This can be a bit faster, and it will let the remote server optimize your query. If you cache the data in a temporary (or in-memory) table on DB1 in...
Why use a READ UNCOMMITTED isolation level?
... Oracle has "snapshot" by default since I know it, probably decades before Sql Server introduced it. I was quite disappointed when starting with SQL Server and I found out that all concurrency problems were solved using "primitive" locking mechanisms. Never saw "Read uncommitted" in Oracle. And the ...
为什么我们程序员写不出好代码？ - 杂谈 - 清泛网 - 专注C/C++及内核技术
...网络游戏中的玩家，他们将更加关心自己的排名，而不是如何让代码更好。
开发者的重点变成了统计代码所编写的行数、解决bug或把所统计的提交的仓库里。如果代码行数都计算在内的话，原本一个问题只需10行代码即可解决...
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Get the Query Executed in Laravel 3/4
How can I retrieve the raw executed SQL query in Laravel 3/4 using Laravel Query Builder or Eloquent ORM?
20 Answers
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How can I temporarily disable a foreign key constraint in MySQL?
Is it possible to temporarily disable constraints in MySQL?
10 Answers
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