I may be erring towards pedantry here, but say I have a field in a database that currently has two values (but may contain more in future). I know I could name this as a flag (e.g. MY_FLAG) containing values 0 and 1, but should more values be required (e.g. 0,1,2,3,4), is it still correct to call the field a flag?
I seem to recall reading something previously, that a flag should always be binary, and anything else should be labelled more appropriately, but I may be mistaken. Does anyone know if my thinking is correct? If so, can you point me to any information on this please? My googling has turned nothing up!!
Thanks very much :o)
Flags are usually binary because when we say flag it means either it is up(1) or down(0).
Just like it is used in military to flag up and down in order to show the war-signs. The concept of flagging is taken from there.
Regarding what you are saying
"your words : values be required (e.g. 0,1,2,3,4)"
In such a situation use Enum. Enumerations are build for such cases or sometimes what we do is , we justify the meaning of these numeric values in comments or in separate file so that more memory could be saved(we use tinyInt or bit field). But never name such a situation Flag.
Flags have standard meaning that is either Up or Down. It doesn't mean that you will get error or something but it is not a good practice. Hope you get it.
It's all a matter of conventions and the ability to maintain your database/code effectively. Technically, you can have a column called my_flag defined as a varchar and hold values like "batman" and "barak obama".
By convention, flags are boolean. If you intend to have other values there, it's probably a better idea to call the column something else, like some_enum, or my_code.
Very occasionally, people talk about (for example) tri-state flags, but Wikipedia and most of the dictionary definitions that I read reserve "flag" for binary / two state uses1.
Of course, neither Wikipedia or any dictionary has the authority to say some English usage is "incorrect". "Correct" usage is really "conventional" usage; i.e. what other people say / write.
I would argue that saying or writing "tri-state flag" is unconventional, but it is unambiguous and serves its purpose of communicating a concept adequately. (And the usage can be justified ...)
1 - Most, but not all; see http://www.oxforddictionaries.com/definition/english/flag.
Don't call anything "flag". Or "count" or "mark" or "int" or "code". Name it like everything else in code: after what it means.
workday {mon..fri}
tall {yes,no}
zip_code {00000..99999}
state {AL..WY}
Notice that (something like) yes/no plays the 'flag' role of indicating a permanent dichotomy. (In lieu of boolean, which does that in the rest of the universe outside SQL). For when the specification/contract really is whether something is so. If a design might add more values you should use a different type.
Of course if you want to add more info to a name you can. Add distinctions that are meaningful if you can.
workday {monday..friday}
workday_abbrev {mon..fri}
is_tall {yes,no}
zip_plus_5 {00000-99..99999-99}
state_name {Alabama..Wyoming}
state_2 {AL..WY}
Related
I imported my data into Stata, and the program is reading some of the variables as strings, but not all of them. And I cannot understand what I did wrong, as some variables are being read as numbers. Is there a way in Stata to turn the string into numeric?
destring is intended for this situation, but the real question is why Stata read your variables as string when you think they should be numeric.
Some of the reasons commonly met are
There is metadata in your data, especially if the data were read in from a file that has spent time in a spreadsheet. Rows of header information or endnotes can cause this problem.
A missing data code has been used that Stata doesn't recognise, say NA for missing.
Decimal points are indicated by say commas, not stops or periods.
The options of destring are often critical, as you may need to spell out what should be done. So, study the help for destring.
If a variable to you should be numeric, but it's not clear why not, something like
tab myvar if missing(real(myvar))
shows the kinds of values of myvar that can't be converted easily. Very often it becomes clear quickly that there is one repeated problem for which there is one overall fix.
I came across some existing code in our production environment given to us by our vendor. They use a string to store comma seperated values to store filtered results from a DB. Keep in mind that this is for a proprietary scripting language called PowerOn that interfaces with a database residing on an AIX system, but it's a language that supports strings, integers, and arrays.
For example, we have;
Account
----------------
123
234
3456
28390
The psuedo code might look like;
Define accounts As String
For Each Account
accounts=accounts + CharCast(Account) + ","
End
as opposed to something I would expect to see like
Define accounts As Integer Array(99)
Define index as Integer=0
For Each Account
accounts(index)=Account
index=index+1
End
By the time the loop is done, accounts will look like; 123,234,3456,28390,. The string is later used to test if a specific instance exists like so
If CharSearch("28390", accounts) > 0 Then Call DoSomething
In the example, the statement evaluates to true and DoSomething gets called. Given the option of arrays, why would want to store integer values whithin a string of comma seperated values? Every language I've come across, it's almost always more expensive to perform string based operations than integer based operations.
Considering I haven't seen this technique before and my experience is somewhat limitted, is there a name for this? Is this common practice or is this just another example of being too stringly typed? To extend the existing code, should I continue using string method? Did we get cruddy code from our vendor?
What I put in the comment still holds but my real answer is: It's probably a design decision with respect to compatibility/portability. In your integer-array case (and a low enough level of the API) you'd typically find yourself asking questions like, what's a safe guess of the size of an integer on "today"'s machines. What about endianness.
The most portable and most flexible of all data formats always has been and always will be printed representation. It may not be as fast to process that but that's where adapters/converters or so kick in. I wouldn't be surprised to find (human-readable) printed representation of something especially in database APIs like you describe.
If you want something fast, just take whatever is given to you, convert it to a more efficient internal format, do you processing and convert it back.
There's nothing inherently wrong with using comma-separated strings instead of arrays. Sure you can't readily access a random n's element of such a collection, but if such random access is not needed then there's no penalty for it, right?
As far as I know Oracle DB stores NUMBER values as strings (and if my memory is correct - for DATEs as well) for very practical reasons.
In your specific example looks like using strings is an overkill when dealing with passing data around without crossing the process boundaries. But could it be that the choice of string data type makes more sense when sending data over wire or storing on disk?
For example a user preference like "display my email to other users" which they can set or unset with a checkbox.
It's a single bit of information, so do you set the field as INT(1) or BOOLEAN, do you set it as one or zero (with a default of zero), or as one or NULL. How about a SET with two possible values, 'yes' and 'no'?
I can't see any huge differences between them, or gotchas. What's best practice?
EDIT: forgot to say, the language with which you test that value might be a factor. If you have a built-in undef or false so you can test with
if($show_email)
is that better than
if($show_email == something)
?
NULL should represent "I do not know the answer", whereas True or False should represent "I know the answer, and it is [True | False]"
Whether there are benefits to storing the "bit" as a specific data type may depend on the specific database platform you are using. For DB platforms without an explicit Boolean data type, it's probably a safe approach to use the smallest integral (e.g. TINYINT) data type if you don't have better guidance for that platform.
I think I'd prefer a 1 or zero myself. And that'd probably work on a lot of database servers (and a lot of apps.) I'll just toss out that I also see CHAR(1) with 'y' or 'n' used a lot. Which of course means you have to check for case and all that, but it does save a little space if that's a concern.
I personally wouldn't allow NULLs. That adds a bunch more conditions to check for at the app level, doesn't it?
From first glance, it would appear I have two basic choices for storing ZIP codes in a database table:
Text (probably most common), i.e. char(5) or varchar(9) to support +4 extension
Numeric, i.e. 32-bit integer
Both would satisfy the requirements of the data, if we assume that there are no international concerns. In the past we've generally just gone the text route, but I was wondering if anyone does the opposite? Just from brief comparison it looks like the integer method has two clear advantages:
It is, by means of its nature, automatically limited to numerics only (whereas without validation the text style could store letters and such which are not, to my knowledge, ever valid in a ZIP code). This doesn't mean we could/would/should forgo validating user input as normal, though!
It takes less space, being 4 bytes (which should be plenty even for 9-digit ZIP codes) instead of 5 or 9 bytes.
Also, it seems like it wouldn't hurt display output much. It is trivial to slap a ToString() on a numeric value, use simple string manipulation to insert a hyphen or space or whatever for the +4 extension, and use string formatting to restore leading zeroes.
Is there anything that would discourage using int as a datatype for US-only ZIP codes?
A numeric ZIP code is -- in a small way -- misleading.
Numbers should mean something numeric. ZIP codes don't add or subtract or participate in any numeric operations. 12309 - 12345 does not compute the distance from downtown Schenectady to my neighborhood.
Granted, for ZIP codes, no one is confused. However, for other number-like fields, it can be confusing.
Since ZIP codes aren't numbers -- they just happen to be coded with a restricted alphabet -- I suggest avoiding a numeric field. The 1-byte saving isn't worth much. And I think that that meaning is more important than the byte.
Edit.
"As for leading zeroes..." is my point. Numbers don't have leading zeros. The presence of meaningful leading zeros on ZIP codes is yet another proof that they're not numeric.
Are you going to ever store non-US postal codes? Canada is 6 characters with some letters. I usually just use a 10 character field. Disk space is cheap, having to rework your data model is not.
Use a string with validation. Zip codes can begin with 0, so numeric is not a suitable type. Also, this applies neatly to international postal codes (e.g. UK, which is up to 8 characters). In the unlikely case that postal codes are a bottleneck, you could limit it to 10 characters, but check out your target formats first.
Here are validation regexes for UK, US and Canada.
Yes, you can pad to get the leading zeroes back. However, you're theoretically throwing away information that might help in case of errors. If someone finds 1235 in the database, is that originally 01235, or has another digit been missed?
Best practice says you should say what you mean. A zip code is a code, not a number. Are you going to add/subtract/multiply/divide zip codes? And from a practical perspective, it's far more important that you're excluding extended zips.
Normally you would use a non-numerical datatype such as a varchar which would allow for more zip code types. If you are dead set on only allowing 5 digit [XXXXX] or 9 digit [XXXXX-XXXX] zip codes, you could then use a char(5) or char(10), but I would not recommend it. Varchar is the safest and most sane choice.
Edit: It should also be noted that if you don't plan on doing numerical calculations on the field, you should not use a numerical data type. ZIP Code is a not a number in the sense that you add or subtract against it. It is just a string that happens to be made up typically of numbers, so you should refrain from using numerical data types for it.
From a technical standpoint, some points raised here are fairly trivial. I work with address data cleansing on a daily basis - in particular cleansing address data from all over the world. It's not a trivial task by any stretch of the imagination. When it comes to zip codes, you could store them as an integer although it may not be "semantically" correct. The fact is, the data is of a numeric form whether or not, strictly speaking it is considered numeric in value.
However, the very real drawback of storing them as numeric types is that you'll lose the ability to easily see if the data was entered incorrectly (i.e. has missing values) or if the system removed leading zeros leading to costly operations to validate potentially invalid zip codes that were otherwise correct.
It's also very hard to force the user to input correct data if one of the repercussions is a delay of business. Users often don't have the patience to enter correct data if it's not immediately obvious. Using a regex is one way of guaranteeing correct data, however if the user enters a value that doesn't conform and they're displayed an error, they may just omit this value altogether or enter something that conforms but is otherwise incorrect. One example [using Canadian postal codes] is that you often see A0A 0A0 entered which isn't valid but conforms to the regex for Canadian postal codes. More often than not, this is entered by users who are forced to provide a postal code, but they either don't know what it is or don't have all of it correct.
One suggestion is to validate the whole of the entry as a unit validating that the zip code is correct when compared with the rest of the address. If it is incorrect, then offering alternate valid zip codes for the address will make it easier for them to input valid data. Likewise, if the zip code is correct for the street address, but the street number falls outside the domain of that zip code, then offer alternate street numbers for that zip code/street combination.
No, because
You never do math functions on zip code
Could contain dashes
Could start with 0
NULL values sometimes interpreted as zero in case of scalar types
like integer (e.g. when you export the data somehow)
Zip code, even if it's a number, is a designation of an area,
meaning this is a name instead of a numeric quantity of anything
Unless you have a business requirement to perform mathematical calculations on ZIP code data, there's no point in using an INT. You're over engineering.
Hope this helps,
Bill
ZIP Codes are traditionally digits, as well as a hyphen for Zip+4, but there is at least one Zip+4 with a hyphen and capital letters:
10022-SHOE
https://www.prnewswire.com/news-releases/saks-fifth-avenue-celebrates-the-10th-birthday-of-its-famed-10022-shoe-salon-300504519.html
Realistically, a lot of business applications will not need to support this edge case, even if it is valid.
Integer is nice, but it only works in the US, which is why most people don't do it. Usually I just use a varchar(20) or so. Probably overkill for any locale.
If you were to use an integer for US Zips, you would want to multiply the leading part by 10,000 and add the +4. The encoding in the database has nothing to do with input validation. You can always require the input to be valid or not, but the storage is matter of how much you think your requirements or the USPS will change. (Hint: your requirements will change.)
I learned recently that in Ruby one reason you would want to avoid this is because there are some zip codes that begin with leading zeroes, which–if stored as in integer–will automatically be converted to octal.
From the docs:
You can use a special prefix to write numbers in decimal, hexadecimal, octal or binary formats. For decimal numbers use a prefix of 0d, for hexadecimal numbers use a prefix of 0x, for octal numbers use a prefix of 0 or 0o…
I think the ZIP code in the int datatype can affect the ML-model. Probably, the higher the code can create outlier in the data for the calculation
In the last 3 companies I've worked at, the phone number columns are of type varchar(n). The reason being that they might want to store extensions (ext. 333). But in every case, the "-" characters are stripped out when inserting and updating. I don't understand why the ".ext" characters are okay to store but not the "-" character. Has any one else seen this and what explanation can you think of for doing it this way? If all you want to store is the numbers, then aren't you better off using an int field? Conversely, if you want to store the number as a string/varchar, then why not keep all the characters and not bother with formatting on display and cleaning on write?
I'm also interested in hearing about other ways in which phone number storage is implemented in other places.
Quick test: are you going to add/subtract/multiply/divide Phone Numbers? Nope. Similarly to SSNs, Phone Numbers are discrete pieces of data that can contain actual numbers, so a string type is probably most appropriate.
one point with storing phone numbers is a leading 0.
eg: 01202 8765432
in an int column, the 0 will be stripped of, which makes the phone number invalid.
I would hazard a guess at the - being swapped for spaces is because they dont actually mean anything
eg: 123-456-789 = 123 456 789 = 123456789
Personally, I wouldn't strip out any characters, as depending on where the phone number is from, it could mean different things. Leave the phone number in the exact format it was entered, as obviously that's the way the person who typed it in is used to seeing it.
It doesn't really matter how you store it, as long as it's consistent. The norm is to strip out formatting characters, but you can also store country code, area code, exchange, and extension separately if you have a need to query on those values. Again, the requirement is that it's consistent - otherwise querying it is a PITA.
Another reason I can think of not to store phone numbers as 'numbers' but as strings of characters, is that often enough part of the software stack you'd use to access the database (PHP, I am looking at you) wouldn't support big enough integers (natively) to be able to store some of the longer and/or exotic phone numbers.
Largest number that 32-bits can carry, without sign, is 4294967295. That wouldn't work for just any Russian mobile phone number, take, for instance, the number 4959261234.
So you have yourself an extra inconvenience of finding a way to carry more than 32-bits worth of number data. Even though databases have long supported very large integers, you only need one bad link in the chain for a showstopper. Like PHP, again.
Stripping some characters and allowing others may have an impact if the database table is going to drive another system, e.g. IP Telephony of some sort. Depending on the systems involved, it may be legitimate to have etc.333 as a suffix, whereas the developers may not have accounted for "-" in the string (and yes, I am guessing here...)
As for storing as a varchar rather than an int, this is just plain-ole common sense to me. As mentioned before, leading zeros may be stripped in an int field, the query on an int field may perform implicit math functions (which could also explain stripping "-" from the text, you don't want to enter 555-1234 and have it stored as -679 do you?)
In short, I don't know the exact reasoning, but can deduce some possibilities.
I'd opt to store the digits as a string and add the various "()" and "-" in my display code. It does get more difficult with international numbers. We handle it by having various "internationalized" display formats depending on country.
What I like to do if I know the phone numbers are only going to be within a specific region, such as North America, is to change the entry into 4 fields. 3 for area code, 3 for prefix, 3 for line, and maybe 5 for extension. I then insert these as 1 field with '-' and maybe an 'e' to designate extension. Any searching of course also needs to follow the same process. This ensures I get more regular data and even allows for the number to be used for actually making a phone call, once the - and the extension are removed. I can also get back to original 4 fields easily.
Good stuff! It seems that the main point is that the formatting of the phone number is not actually part of the data but is instead an aspect of the source country. Still, by keeping the extension part of the number as is, one might be breaking the model of separating the formatting from the data. I doubt that all countries use the same syntax/format to describe an extension. Additionally, if integrating with a phone system is a (possible) requirement, then it might be better to store the extension separately and build the message as it is expected. But Mark also makes a good point that if you are consistent, then it probably won't matter how you store it since you can query and process it consistently as well.
Thank you Eric for the link to the other question.
When an automated telephone system uses a field to make a phone call it may not be able to tell what characters it should use and which it should ignore in dialing. A human being may see a "(" or ")" or "-" character and know these are considered delimiters separating the area code, npa, and nxx of the phone number. Remember though that each character represents a binary pattern that, unless pre-programmed to ignore, would be entered by an automated dialer. To account for this it is better to store the equivalent of only the characters a user would press on the phone handset and even better that the individual values be stored in separate columns so the dialer can use individual fields without having to parse the string.
Even if not using dialing automation it is a good practice to store things you dont need to update in the future. It is much easier to add characters between fields than strip them out of strings.
In comment of using a string vs. integer datatype as noted above strings are the proper way to store phone numbers based on variations between countries. There is an important caveat to that though in that while aggregating statistics for reporting (i.e. SUM of how many numbers or calls) character strings are MUCH slower to count than integers. To account for this its important to add an integer as an identity column that you can use for counting instead of the varchar or char field datatype.