January 2015 Archive

Deletion / Updates

A deletion statement consists of: 1. The keywords DELETE FROM, 2. The name of a relation, say R, 3. The keyword WHERE, and 4. A condition. That is, the form of a deletion is DELETE FROM R WHERE ; The effect of executing this statement is that every tuple satisfying the condition (4) will be deleted from relation R.

Defining a Relation Schema in SQL

Now we shall begin a discussion of data definition, the portions of SQL that involve explaining the structure of information in the database. On the contrary, the aspects of SQL discussed previously - queries and modifications - are often called data manipulation.

Simple Table Declarations

The simplest form of declaration of a relation schema comprises the keywords CREATE TABLE followed by the name of the relation and a parenthesized list of the attribute names and their types.

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