Java and Database Connectivity

SQL: Reprise

Table:

• a set of similar namespaces (rows)
• representing a kind of thing in the domain
• each namespace (row) represents one thing of this kind
  • Like objects in a class... almost.

Primary key:

• a column in a table in which each value is distinct from every other.
• makes the table into a namespace of rows
• not every table has one

Foreign keys

• a column in a table whose values are values from the primary key column in another table
• not every table has one
• some tables have more than one

Join

• A select statement which joins two or more tables
• Usually in ways that represent predetermined relationships
• If mis-constructed (e.g. 'cross-product joins') can go horribly wrong
• Complex joins can be expensive to compute.

Full text of this presentation | Table of Contents | No Frames Author: Simon Brooke | Copyright © 1998-2001 Weft Technology Ltd Slide 59 of 92