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Converting an SQL command that does not contain a sub-query

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Slideshow:

Procedure to convert an SQL query that does not contain a sub-query
 
SQL command that does not contain a sub-query:
 
The corresponding parse tree is as follows:

Procedure to convert an SQL query that does not contain a sub-query
SQL command that does not contain a sub-query:

The corresponding initial query tree is as follows:

Example 1: coverting an SQL query (with no sub-query) into an (initial) query plan
 
The SQL query and the corresponding parse tree:

Example 1: coverting an SQL query (with no sub-query) into an (initial) query plan
Converting the parse tree to its initial (logical) query plan:

Procedure to convert an SQL query that contains a GROUP BY clause
SQL command containing a GROUP BY clause:

The corresponding parse tree is as follows:

Procedure to convert an SQL query that contains a GROUP BY clause
GROUP BY SQL query and its corresponding initial query tree:

Example: coverting a GROUP BY SQL query into an (initial) query plan
 
Converting the parse tree to its initial (logical) query plan:

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• Converting a parse-tree without a sub-query
  • SQL command without a sub-query:

    SELECT a1, a2, a3, ... FROM R1, R2, R3, ... WHERE C

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  • The parse-tree looks like this:

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  • This type of parse tree can be easily converted to an initial logical query plan (tree) as follows:

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• Example conversion
  • Parse-tree:

  • Convert the parse-tree into initial logical query plan:

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• Converting SQL query with a group by clause
  • SQL command without a sub-query:

    SELECT a1, a2, a3, ... max(...) FROM R1, R2, R3, ... WHERE C1 GROUP BY a1, a2, a3, ... HAVING C2

    Note: the select-attributes must be a subset of the grouping attributes !!!

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  • The parse-tree looks like this:

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  • This type of parse tree can be easily converted to an initial logical query plan (tree) as follows:

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  • Example:

    Note:

    The projection πdname,avg(salary)( ) is not needed because: The input to the projection operator πdname,avg(salary)( ) are "dname ,  avg(salary)"           So πdname,avg(salary)( ) will not remove any attribute....