First Accustomed Anatomy (1NF) is the best basal accustomed anatomy of relational database theory. Its purpose is to ensure that the database arrangement has abstracts that it can dispense in a aboveboard manner, so that querying, inserting, and afterlight abstracts is not an foolishly circuitous assignment for the database system. Essentially, it is a affirmation that the abandoned units of abstracts that the database is appropriate to assignment with can consistently be advised by a database arrangement as actuality chargeless of any anatomy added than that authentic by the arrangement of abstracts types accepted by the system. An appliance may accept to abundance abstracts that encodes added anatomy in the database. Because such added anatomy is not inherent in the abstracts types accurate by the database system, the database charge not be appropriate to do annihilation that needs ability of that structure.
1NF is the abandoned one of the frequently recognised accustomed forms that is about the anatomy of a table per se, rather than about how that anatomy should chronicle to the rules of the apple actuality modelled by the tables. 1NF doesn’t affliction about the alien world. It cares abandoned about database internals. In effect, 1NF imposes two rules, a aphorism that the database doesn’t charge to apperceive about annihilation added than database internals and addition aphorism that anniversary table charge accept a primary key.
It is sometimes claimed that it is absurd to breach 1NF in SQL, because SQL enforces 1NF. This is abandoned accurate with a actual attenuated abstruse estimation of 1NF beneath which abounding structures which best bodies attention as actionable 1NF would be admired as not actionable it – a case of afterward the letter but not the spirit, some ability say (I would say that neither the letter nor the spirit is actuality followed, back SQL does not force you to accept a primary key).
Here is the analogue of First Accustomed Form
A table is in 1NF back every cavalcade has a anchored simple data-type that is accepted by the database system, and every row has a primary key.
Sometimes bodies use altered definitions. This isn’t because they are cerebration of altered concepts, but because they are emphasising altered aspects of this analogue and/or because they accomplish altered assumptions about what is already appropriate in the abstracts archetypal for it to be relational (or for it to be a accurate SQL table definition) . For example, bodies may leave off the primary key affirmation because they apperceive that the abject relations of relational database approach are appropriate to accept a primary key; but that’s a annular argument, as a affiliation in relational database approach is appropriate to accommodate to 1NF. Bodies may add a affirmation that all rows accept the aforementioned columns; but that absolutely is allotment of the analogue of a affiliation (even a algebraic relation, let abandoned a relational database relation). The “single simple value” is sometimes alleged an “atomic value”, and sometimes the abstraction is bidding in agreement of repeating groups. A repeating accumulation is a amount that is non-simple because it is a set of ethics – finer the cavalcade contains added than one amount in this row.
Tables that are not in 1NF care to be rare, but they are a approved affection of abominably advised SQL databases. First, we accept tables after a primary key. These won’t be added discussed here, except to say that every abject table should accept a primary key (temporary tables are maybe beneath of a concern). Afresh we accept tables area the database arrangement has to accept some aspect that has a circuitous blazon not accepted by the arrangement – a developer has called to encode some circuitous anatomy in a string, perhaps, and afresh absitively that he needs to use genitalia of that anatomy in database operations.
So let’s attending at a table that ability or ability not breach the simple data- blazon aphorism of 1NF. Actuality are two rows from that table
121 643 4321,
121 643 4497,121 641 3159
Is this or isn’t it in 1NF? That depends on what the database is accepted to do with it.
With the telephones cavalcade there are two possibilities.
Perhaps all the database has to do with the telephones cavalcade is bear the ethics it holds to an app and acquiesce an app to overwrite the amount in that cavalcade with a new value. Afresh it is up to the appliance and not the database to break that amount into three numbers and apperceive what they are (office phone, appointment fax, home phone). It is additionally the app’s job to encode the three numbers into a amount to put into the cavalcade – the database doesn’t apperceive annihilation about that encoding. The cavalcade is aloof a simple cord amount so far as the database is concerned. In that case there is no abuse of 1NF by the telephones cavalcade – it’s a repeating accumulation as far as the appliance is concerned, but the database arrangement doesn’t charge to apperceive that.
The added achievability is that you appetite adaptation and encoding done in the database instead of in the application. There will accept to be cipher in queries to break that circuitous cord and abstract the altered numbers; and alike afresh you won’t get an able chase on any of the numbers, as there’s no way that adaptation operation will admittance use of an basis to aid the search. The table violates 1NF, and the aftereffect is clumsily complicated concern cipher and a abundant achievement penalty.
With the Marital Status column, there are afresh two possibilities. Maybe the encoding and adaptation of that cord is consistently in the app, and the database aloof sees a distinct varchar value, in which case there is no abuse of 1NF. Or conceivably the database will be asked to break questions like “list all bodies who are affiliated to addition beneath that 21 years old”, in which case it has to break that cavalcade and 1NF is abandoned afresh – and afresh there are cipher complication and achievement penalties.
Let’s attending at what to do in the case area both these columns are breaking the “single simple value” aphorism of 1NF because the database is accepted to handle the adaptation and encoding.
First the telephones column. If everybody has an appointment phone, an appointment fax number, and a home buzz we can aloof about-face the distinct telephones cavalcade into three columns: OfficePhone, OfficeFax, and HomePhone. What if some bodies don’t accept an appointment fax number? Some bodies would still use the three columns, application a asinine cardinal like 000 000 0000 to announce “no such number”. That’s bigger than application NULL to announce “no such number”. Usually a still bigger band-aid (better by far) is to acquaint a new table OfficeFax that has a name cavalcade and a FaxNumber cavalcade – addition who doesn’t accept an appointment fax cardinal doesn’t appearance up in this table, so the use of NULLs or asinine ethics is avoided.
Next the Marital Status column. This cavalcade could be breach into SpouseName and SpouseDoB but that would apparently end up application NULL (or a zero-length string, which is hardly bigger than NULL) in the SpouseName cavalcade to announce “unmarried”. It’s no acceptable aggravating a asinine cord like ‘zqxrdlsprrgj’ because accordingly some apron will accurately change his or her name to ‘zqxrdlsprrgj’ aloof to blend with the system. This NULL or aught breadth cord will additionally acquaint you to avoid the SpouseDoB column, because it’s irrelevant. Addition achievability is to accumulate the Marital Status cavalcade as able-bodied as the SpouseName and SpouseDoB column, and ‘Single’ in that cavalcade tells you to avoid the added two. Again, accepting an added table MaritalStatus with columns Name, SpouseName, SpouseDoB will usually be the best bet. Names of bachelor bodies won’t action in that table, so names and DoB of absent spouses don’t accept to be recorded as NULL or as annihilation else.
Don’t let anyone acquaint you that table which has a nullable cavalcade does not, for that acumen alone, accommodate to 1NF; this is a affirmation fabricated abandoned by bodies who don’t accept area theory. Equally, don’t let anyone acquaint you that you should use NULLs foolishly to aish repeating groups (or added non-simple types) in cases like those declared above. Use of NULL in cases like these is absolutely an attack to ad-lib a table area altered rows accept altered numbers of columns, and should never be done after actual accurate appraisal of the alternatives. Back such appraisal takes place, it will about consistently announce that application NULL is not the best solution.
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