34,333
edits
Changes
→Introducing Database Schema
== Introducing Database Schema ==
''Database Schema'' define the characteristics of the data stored in a database table. For example, the table schema for a customer database table might define that the customer name is a string of no more than 20 characters in length, and that the customer phone number is a numerical data field of a certain format.
Schema are also used to define the structure of entire databases and the relationship between the various tables contained in each database.
== Columns and Datatypes ==
It is helpful at this stage to begin to view a database table as being similar to a spreadsheet where data is stored in rows and columns.
Each column represents a data field in the corresponding table. For example, the name, address and telephone data fields of a table are all ''columns''.
Each column, in turn, is defined to contain a certain ''datatype'' which dictates the type of data the column can contain. A column designed to store numbers would, therefore, be defined as a numerical datatype.
== Database Rows ==
Each new record that is saved to a table is stored in a row. Each row, in turn, consists of the columns of data associated with the saved record.
Once again, consider the spreadsheet analogy described earlier in this chapter. Each entry in a customer table is equivalent to a row in a spreadsheet and each column contains the data for each customer (name, address, telephone etc). When a new customer is added to the table, a new row is created and the data for that customer stored in the corresponding columns of the new row.
''rows'' are also somethings referred to as ''records'' and these terms can generally be used interchangeably.
