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Postscript: converting SQL parse tree to initial query plan

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• Recall: the simplified SQL syntax used
  • The text book only handles the conversion of SQL queries using the following simplified SQL syntax:

    <Query> ::= SELECT <SelList> FROM <FromList> WHERE <Condition> <SelList> ::= <Attribute> | <Attribute> , <SelList> <FromList> ::= <Relation> | <Relation> , <FromList> <Condition> ::= <Condition> AND <Condition> | <Attribute> IN ( <Query> ) | <Attribute> = <Attribute> | <Attribute> LIKE <Pattern>

    The only condition containing a sub-query is the IN clause

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• For your reference
  • A more general treatise on converting an SQL SELECT clause to a relation algebra expression (tree) is presenting in this article:

    Translating SQL into the Relational Algebra

    The general treatise is outside the scope of this course...