Chapter 3 Database Design Exam Questions And Correct Answers All 100% Verified

Chapter 3 Database Design Exam Questions And Correct Answers All 100% Verified Primary Key - Answer -Is a column, or a group of columns, used to identify a row. The primary key is usually the tables 1st column, and appears on the left of table diagrams, but the position is not significant to the database. * often, primary key values are used in the WHERE clause to select a specific row. * Primary keys must be: - Answer -- Unique: this rule ensures that each value identifies at most one row. -Not NULL: this rule ensures that each value identifies at least one row. Simple primary key - Answer -consists of a single column. Composite primary key - Answer -Consist of multiple columns. Composite primary keys are denoted with parentheses. Ex: (ColumnA, ColumnB). Ex: (ID Number) Composite primary keys must be: - Answer -•Unique: values of primary key columns, when grouped together, must be unique. No group of values may repeat in multiple rows. •Not NULL: column of a composite primary key may contain a NULL value. •Minimal: all primary key columns are necessary for uniqueness. When any column is removed, the resulting simple or composite column is no longer unique. PRIMARY KEY constraint - Answer -This constraint in a CREATE TABLE statement names the tables primary key. This ensures, that the column or group of comms is always unique and non-null. Auto-increment column - Answer -A numeric column whose value is generated automatically when a row is added to the table. AUTO_INCREMENT - Answer -May only be applied to primary key columns