The ALTER TABLE statement is part of the Data Definition Language (DDL). The statement is used to modify a table after it has been created. Today, I would like to talk about the three integrity concerns that data modelers deal with. Integrity Concerns Entity Data Integrity – Adding primary keys to makes sure rows are unique. Referential Data Integrity – Adding foreign keys to make sure relationships are maintained. Domain Data Integrity – Creating constraints or triggers enforce the range of data values. Again, we will be working with the…
Day: August 23, 2011
Crafting Databases – Part 3
The CREATE TABLE statement is part of the Data Definition Language (DDL). It is used to define a structure to hold rows of data or tuples if we use Relational Algebra concepts. Each table is defined by a set of fields of a certain data type and precision. Data Types can be categorized as the following. Exact numerics Approximate numerics Character strings Unicode character strings Binary strings Date and time Other data types The power of a database comes from creating user defined datatypes (UDT). Some of the benefits of…