I have no experience in SQl databases. I just started using ActiveRecord and I find myself compy pasting the ActiveRecord query statements beucase I don't know difference between when to use .find() .where(), joins etc. There's so many ways to do one query and I am ovewhemled. I am just wondering if it's a good idea to take a step back and learn SQL first or jus try to follow along? Also if what's the best way to learn SQL?
Thanks
Yes! You should definitely know SQL to use ActiveRecord effectively.
AR improves productivity by abstracting you away from the tedium of writing raw SQL, but an understanding of what it's doing will improve your usage of it, as well as your ability to write effective code.
You could start by watching your logs with tail -f log/development.log while you work, which will show you the statements generated by AR. This will help you gain a frame of reference to help you see what AR is doing for a given call.
AR doesn't replace SQL - it augments it by letting you use it at a higher level. Understanding what's going on under the hood will only help you.
I would definitely recommend learning SQL first, it will help you out ALOT in the long run. Active Record really is just an Object-Relational Mapping of the database that helps to make writing the SQL cleaner, clearer, and easier. That being said I do not think it is a replacement to know SQL, not to mention it is pretty easy to learn the basics. I would suggest looking at both documentation on SQL as well as active record.
SQL: http://www.w3schools.com/sql/default.asp
Active Record: http://guides.rubyonrails.org/active_record_querying.html And http://api.rubyonrails.org/classes/ActiveRecord/Base.html
If you know SQL basics then it's easy to use ActiveRecord.
To learn SQL basics you can use this link.
To learn ActiveRecord use this link.
Related
I cannot find the difference between to two in my search on SO. Can someone explain the difference to me? I feel pretty confident on my understanding of an ORM. But I do not know what SQL Mapping is, and therefore how it is different from an ORM.
I am using Java if it matters.
I control all of the database.
Is there an example of a small understandable SQL Mapper I could look at?
EDIT: I really do not want to embed SQL in my code. That's the devil.
I would like to create my own query language for a web api I wrote. But I have no idea where to start for it.
The language should be like SQL. For that I looked up the NHibernate code, cause I know, that they have the HQL (Hibernate Query Language) but it didn't help.
Are there any instructions or sth.? If this question is wrong here please move and/or tell me where I should ask else.
The first step is a lot of design work, starting be answering the following question:
Is this new Query Language going to be converted to SQL which will be
executed by a standard database engine, or are you going to write your
own database server as well?
If it's going to be converted to SQL (just like HQL) then map out the translations from your language to SQL on paper (and make sure you know the possible SQL constructs you may have to use). Once you've got that, you can start implementing it. Yes, this sounds like BDUF, but the language should be defined in one pass, I think, as it will be more consistent and easier to use if you do it that way. You can always implement it in a more Agile way once you've got that.
If you're going to write own database server, you're on your own....
Please help me in this, I know only basic queries in sql, and where can I start from sql query and become expert in that?
What are all the steps to follow and books to learn?
For Oracle db, see here. You'll want to learn as much ansi SQL as you can, but each db will have features that you'll want to exploit as well.
To become good in what you do, you have to like what you do.
google how to become oracle guru
If you like what you do, you are most likely to spend lots of time learning things by experimenting and making many errors. From errors we learn.... (happens to be my blog name)
You can follow this very good step-by-step guide
I have been using MySQL for years, mainly on smaller projects until the last year or so. I'm not sure if it's the nature of the language or my lack of real tutorials that gives me the feeling of being unsure if what I'm writing is the proper way for optimization purposes and scaling purposes.
While self-taught in PHP I'm very sure of myself and the code I write, easily can compare it to others and so on.
With MySQL, I'm not sure whether (and in what cases) an INNER JOIN or LEFT JOIN should be used, nor am I aware of the large amount of functionality that it has. While I've written code for databases that handled tens of millions of records, I don't know if it's optimum. I often find that a small tweak will make a query take less than 1/10 of the original time... but how do I know that my current query isn't also slow?
I would like to become completely confident in this field in the ability to optimize databases and be scalable. Use is not a problem -- I use it on a daily basis in a number of different ways.
So, the question is, what's the path? Reading a book? Website/tutorials? Recommendations?
EXPLAIN is your friend for one. If you learn to use this tool, you should be able to optimize your queries very effectively.
Scan the the MySQL manual and read Paul DuBois' MySQL book.
Use EXPLAIN SELECT, SHOW VARIABLES, SHOW STATUS and SHOW PROCESSLIST.
Learn how the query optimizer works.
Optimize your table formats.
Maintain your tables (myisamchk, CHECK TABLE, OPTIMIZE TABLE).
Use MySQL extensions to get things done faster.
Write a MySQL UDF function if you notice that you would need some
function in many places.
Don't use GRANT on table level or column level if you don't really need
it.
http://dev.mysql.com/tech-resources/presentations/presentation-oscon2000-20000719/index.html
The only way to become an expert in something is experience and that usually takes time. And a good mentor(s) that are better than you to teach you what you are missing. The problem is you don't know what you don't know.
Research and experience - if you don't have the projects to warrant the research, make them. Make three tables with related data and make up scenarios.
E.g.
Make a table of movies their data
make a table of user
make a table of ratings for users
spend time learning how joins work, how to get movies of a particular rating range in one query, how to search the movies table ( like, regex) - as mentioned, use explain to see how different things affect speed. Make a day of it; I guarantee your
handle on it will be greatly increased.
If you're still struggling for case-scenarios, start looking here on SO for questions and try out those scenarios yourself.
I don't know if MIT open courseware has anything about databases... Well whaddya know? They do: http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-830Fall-2005/CourseHome/
I would recommend that as one source based only on MITs reputation. If you can take a formal course from a university you may find that helpful. Also a good understanding of the fundamental discrete mathematics/logic certainly would do no harm.
As others have said, time and practice is the only real approach.
More practically, I found that EXPLAIN worked wonders for me personally. Learning to read the output of that was probably the biggest single leap I made in being able to write efficient queries.
The second thing I found really helpful was SQL Tuning by Dan Tow, which describes a fairly formal methodology for extracting performance. It's a bit involved, but works well in lots of situations. And if nothing else, it will give you a much better understanding of the way joins are processed.
Start with a class like this one: https://www.udemy.com/sql-mysql-databases/
Then use what you've learned to create and manage a number of SQL databases and run queries. Getting to the expert level is really about practice. But of course you need to learn the pieces before you can practice.
I know that in most cases it`s more useful to learn more complicated technology/language and then easy one than vice versa.
But, actually, time to do university tasks is limited. If I first learn LINQ, then go for SQL, would it be hard for me to use and learn sql?
EDIT
The task I need to do is to work with database and get some data from it, so the question is almost about LINQ to SQL.
It is a bad idea.
And if today's universities teach you LINQ instead of giving you foundation to build your knowledge upon, I can only feel sorry and pity for their students.
Time is always limited. Don't waste it on things that are subject to constant change.
SQL will be there tomorrow, LINQ.... well who knows.
SQL is applicable anywhere, LINQ only in .NET world.
Either LINQ or something else, it will be easy to "learn" it afterwards. When you have the knowledge of SQL, it will just me a matter of hours/days/weeks, hardly longer.
Well, the 2 things are very different. LINQ (in the pure sense) isn't actually related to databases at all - it can be used quite happily just with in memory objects, or against web services, etc.
If you are mainly interested in writing better .NET code, then learn LINQ - but learn it properly - perhaps pick up C# in Depth, for example - which covers it very well in the last few chapters.
If you want to know about databases, then sure: learn SQL (such as TSQL) - but understand the differences. Databases are good if you need to write enterprise software, but not necessarily if you just want to do simple tasks.
edit re edit to the question
If you are just getting simple data in and out of the database, then you probably don't need to know much about SQL. Just use LINQ-to-SQL (or whatever tool), and let the ORM tooling worry about it.
Learn SQL first, then LINQ.
That way you'll understand how LINQ-to-SQL is working behind the scenes, but you'll also know enough to be able to cope when LINQ can't do what you need.
SQL is a standard, learn the standard.
More precisely :
learn database theory
learn CODD algebra
then pick up a "common database", do some tutorials on it, ...
I personnaly really like PostgreSQL tutorial
I submit that you cannot effectively use LINQ unless you have SQL knowledge. If you don't understand, at a minimum, the following, you cannot effectively query a database in any fashion:
select
insert
delete
update
joins
group by
boolean algebra
relational theory
set theory
Learning SQL will give you the concepts you need even if you use LINQ later.
Sql. However you could play with linq pad for a while - it is a freeware and realize that LINQ is a nice hybrid between SQL and C#