SQL Notes.docx

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Ryerson University
Information Technology Management
ITM 500
Raymond Moss

SELECT FROM WHERE GROUP BY HAVING ORDER BY WHERE vs. HAVING: - 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. Common aggregate functions include:  Average()  Count()  Maximum()  Mean()  Minimum()  Mode()  Sum() Weak entity rule - At least one identifying relationship - Cannot be a weak entity without at least one identifying relationship Identifying relationship rule: - At least one participating relationship must be weak - Not an identifying relationship if there is not a weak entity Identification dependency cardinality rule: - Minimum and maximum cardinality must (1,1) for a weak entity in all identifying relationships - (1,1) cardinality should appear near the parent entity type - Common source of diagram errors 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---F
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