ITM 500 Chapter Notes -Aggregate Function

• School: Ryerson University
• Department: Information Technology Management
• Course: ITM 500
• Professor: Raymond Moss

Document Summary

Where conditions: cannot have aggregate functions (syntax error) Having: only use conditions that involve an aggregate function aggregate function is a function that returns a single value from a collection of input values such as a set, a bag or a list. Cannot be a weak entity without at least one identifying relationship. At least one participating relationship must be weak. Not an identifying relationship if there is not a weak entity. Minimum and maximum cardinality must (1,1) for a weak entity in all identifying relationships. Common source of diagram errors (1,1) cardinality should appear near the parent entity type. There are three types of outer joins namely: Left outer join---for retreiving all the columns from the first table irrespective of the column match. Right outer join---for retreiving all the columns from the second table irrespective of the column match. Full outer join---for retreiving all the columns from both the tables irrespective of column match.