Multiplication table - Wikipedia
In mathematics, a multiplication table is a mathematical table used to define a multiplication 5, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 6, 6, 12, 18, 24, 30 . of the many-many table then EF cannot and will not treat that as an implicit many-many collection. share improve this answer. answered Sep 25 '13 at July , Appendix table Employees aged by type of employment relationship /07 - / Helsinki: Statistics Finland.
More to the point, what is a key, and what is a primary key, and why should I care? Setting up correct table relationships is the second half of good database design.
Defining relationships between tables is how you pull that related data back together again. Field Names and Data Types Once you have designed your tables, creating them in Access is pretty straightforward.
Field names must be unique within a table but can be reused in other tables. The trickier part is assigning a data type to each field. Unlike with a table in a Word document, for example, with an Access table you must specify what kind of data you intend to put in each field. Because a database knows what kinds of values are in a specific type of field, it can sift, collate, sort, and view different slices of data in myriad ways and can prevent some kinds of data from interacting in certain undesirable ways.
Here are some simple rules to follow when choosing data types: For money, use the Currency data type. Here are some very basic guidelines. If your numbers are integers i. So make it a Text field. For foreign keys, you must use the data type of the primary key that the foreign key refers to.
For example, if the primary key is an AutoNumber, use the Number data type with the Field Size set to Long Integer for the foreign key. And duplicate records cause all sorts of headaches. But you can run into different problems with using meaningful fields.
And even with a meaningful key, you can still enter duplicate records if, for example, you use a slightly different spelling of the name. For these reasons, we recommend using an AutoNumber ID field in most cases. Good table design requires that every table have at least one field that acts as a unique key. We call this the primary key field. After all, you could have two customers with the same business name in different states.
The numbers are meaningless—they simply serve as unique identifiers. To see how keys are used to create relationships, consider two tables: So how do you create a report that tracks which order goes with which customer, and presents all that information on one screen? You simply add a field to the orders table that refers to the primary key of the customers table. You may as well call it by the same name, customerId see Figure Incidentally, the customerId field in the orders table is known as a foreign key; it refers to the value of a primary key field in another table.
Customers and orders tables, related by customerId. Right-click anywhere in the Relationships window and select Show Table. Add the tables you want to relate to the Relationships window by highlighting them and clicking the Add button in the Show Table window.
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Then drag the primary key field from one table and drop it onto the matching foreign key field in the other table. The Edit Relationships dialog will open. Click the Create button, and Access will draw a line connecting the two tables.
If you ever need to edit or delete the relationship, you can do so by right-clicking the line. Consider the relationship between suppliers and products.
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Several suppliers might supply the same product, and one supplier might supply several different products. Likewise, if you added a productCode field to the suppliers table, each supplier could supply only a single product. Both products and suppliers will have one-to-many relationships to this linking table, enabling each product to have many suppliers and each supplier to supply many products see Figure Products, suppliers, and products-suppliers tables.
Products and suppliers are in a many-to-many relationship. A linking table typically just contains the foreign keys from each of the tables that it links.
Each supplier will appear in this table once for each product supplied, and each product will appear in this table once for each supplier who supplies it. The primary key for this linking table will be a composite key using both fields. I run a small business, and I just need a simple database to handle sales contacts.
Surely this application has been designed a thousand times by people who know Access better than I ever will. You have a variety of options, depending on your needs and how much you can afford to pay. For a very generic contact database, take a look at the prefab database templates that come with Access. Figure shows the Databases tab, with choices such as Contact Management, Expenses, and so on. Selecting one of these will start the Database Wizard, which lets you customize the template a bit.
Diet and its relation to coronary heart disease and death in three populations.
Access comes with templates for common database applications that you can customize with the Database Wizard. You might also poke around in newsgroups or at Utter Access http: Many off-the-shelf Access packages are available for common business needs, and in many cases the seller will customize upon request.
So based on this, it looks like that we have a proportional relationship between y and x. So this one right over here is proportional.
Intro to proportional relationships (video) | Khan Academy
So given that, what's an example of relationships that are not proportional. Well those are fairly easy to construct. So let's say we had-- I'll do it with two different variables. So let's say we have a and b.
And let's say when a is one, b is three. And when a is two, b is six. And when a is 10, b is So here-- you might say look, look when a is one, b is three so the ratio b to a-- you could say b to a-- you could say well when b is three, a is one. Or when a is one, b is three.
So three to one. And that's also the case when b is six, a is two. Or when a is two, b is six. So it's six to two. So these ratios seem to be the same. But then all of sudden the ratio is different right over here.
This is not equal to 35 over So this is not a proportional relationship. In order to be proportional the ratio between the two variables always has to be the same. So this right over here-- This is not proportional.
So the key in identifying a proportional relationship is look at the different values that the variables take on when one variable is one value, and then what is the other variable become?