The data type of the database has a lot of types, which is confusing. I'm still a beginner in programming, so ** "Well, which one should I use in this case?" ** I do a Google search every time, but I couldn't find a good commentary, so I will write an article that also serves as an output! Thank you.
| Data type | type |
|---|---|
| integer | Integer type(4 bytes) |
| bigint | Integer type(8 bytes) |
| decimal | Fixed-length integer type (highly accurate decimal) |
| float | Number (floating point number) |
| string | String(1 to 255 characters) |
| text | Long string(1 〜 4,294,967,296 characters) |
| date | date(1000-01-01 〜 9999-12-31) |
| datetime | Date and time(1000-01-01 00:00:00.000000 〜 9999-12-31 23:59:59.999999) |
| time | Times of Day(-838:59:59 〜 838:59:59) |
| timestamp | Time stamp('1970-01-01 00:00:01' UTC ~ '2038-01-19 03:14:07' UTC) |
| binary | Binary string type |
| boolean | True and false |
| primary_key | Primary key(Primary key) |
Actually, I should explain everything, but I will only cover the parts that I personally care about! For items that are not listed, please try to google for yourself.
** integer **: Integer type (4 bytes) ** bigint **: Integer type (8 bytes)
Suddenly I don't understand from the beginning. Apparently, in the past, integer types were only integers, but when it comes to large-scale SNS sites, the number of members alone has become quite large, and integers can no longer handle it. It seems that.
So, starting with Rails 5.1, the id column has changed to bigint. When creating a new application, there is no particular problem, but if you are using integer in an existing application, it seems that an error may occur when repairing the system.
In the general classification method, it is often used as follows.
** string ** (1 to 255 characters) ·name ·Street address ·password ** text ** (1 to 4,294,967,296 characters) ·comment ・ Posted text
I think that the situation varies depending on the site to be created, so it is just an example.
** timestamp **: Timestamp ('1970-01-01 00:00:01' UTC ~ '2038-01-19 03:14:07' UTC) ** datetime **: Date and time (1000-01-01 00: 00: 00.000000 ~ 9999-12-31 23: 59: 59.999999)
Do you know the ** 2038 problem **!
If you look closely, you may notice that timestamp is currently only available until 2038 ...
I don't know why this happened, but it seems that there is a shift towards using datetime when recording the date and time.
The world is likely to be rough in 2038.
In the first place, "binary" is a computer term, and is a data format in which data is represented by "0" and "1". Rails may recognize it as "a file in which data is written with non-textual information."
The main binary files are ・ Audio file · Image file ・ Compressed file And so on. Binary data is not written in human-readable characters. Therefore, you cannot open binary data with a text editor. I don't know how to use it.
This is also a concept that I don't really understand. In general, it represents a data type that represents two states, such as true and false.
Recognize that there are quite a few types of data types. I learned a lot because I couldn't get to know it unless I put it together in this way.
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