User:Dianna J Cooper/sandbox

All databases have a first column, it revolves around it. Without the primary key, it will fall apart, it is the unique identifier. 95% of database, it starts with a number. All tables have this. Without a primary key, nothing can link to your table. E.g.: you can’t tell how many foreign students there are, because you don’t know how many people are in the school, you don’t know how many cars are sold unless you know the number you started with. You need to know the exact number before you add some more on. If you don’t link primary and foreign key after the link, then they won’t work in a relationship. The primary and foreign key has to link. It is important to link the primary keys from table to table, to either a primary or foreign key, otherwise the tables won’t hold together and the integrity will not work because the information will not be linked and the information will not be able to be generated other than as a flat file.

A foreign key is a column in a table that must link to the primary key. You can have as many as you want. They can be in any column. You can’t link tables together. Every student has a unique number, e.g.; student number is primary key, every person in Britain has a unique number, and you’ll have it throughout your life. National number is your primary key. Every record that looks up that unique number, there is a foreign key. To look at records you need the primary key to do it. E.g.: 42 cars in car park, how many are blue, count the cars, and then count the number of blue ones. This is called data integrity. The foreign key has to link. It is important to link the primary keys from table to table, to either a primary or foreign key, otherwise the tables won’t hold together and the integrity will not work because the information will not be linked and the information will not be able to be generated other than as a flat file. The foreign is less important than the primary key and a table can have as many foreign keys as it wants, but it can only have one primary key.

Fields Every table/record has different unique fields. Every table is constructed with fields. Every part of the table is a separate field, which has a unique construction that limits down the information within the field so that the user can reduce down the potential mistakes that might be made. Field size will restrict down the amount of characters will can write down. E.g.: You can type 100 characters in the field, but if I want 10 characters, I can only type in 10 letters or punctuation such as full stops. Input Mask It works like a postcode, letter letter, number number, letter letter. You can only type a letter then a number, but if you write something else down it will refuse to do it. Eleven zeros, the number has to be eleven different numbers, or I can type something else or leave it blank. The input mask limits postcodes down, so people can’t write in postcodes that don’t exist, not enough numbers or letters, other forms of input mask is the @ symbol, which means you have to type in a valid email address.

Caption Tells you why you can’t write in the input mask, it is a hint or clue, it tells you that you can’t write something in that shouldn’t be in there. Such as if you write the wrong postcode, it will give you a hint that you can’t. You can’t type in the wrong, otherwise it will remove it. Make sure you use capital letters or that your password has a number in it. That is what the hint is for. It is validation text, validation text is a caption to try and help the user make the right choices whilst inputting information.

Validation Rule Allows you restrict down some information, but not all. E.g.: email has @ in it to make it work. That is the input mask. You can put a space in between the @ and the name, that is the validation rule. The validation rule is specific, it limits down something that is numerical such as a rule between one number and another.