com.mckoi.database.interpret
Class Select

java.lang.Object
  extended by com.mckoi.database.interpret.Statement
      extended by com.mckoi.database.interpret.Select

public class Select
extends Statement

Logic for interpreting an SQL SELECT statement.

Author:
Tobias Downer

Field Summary
 
Fields inherited from class com.mckoi.database.interpret.Statement
cmd, database, query, table_list, user
 
Constructor Summary
Select()
           
 
Method Summary
 Table evaluate()
          Evaluates the select statement with the given Database context.
 void prepare()
          Prepares the select statement with a Database object.
 java.lang.String toString()
          Outputs information for debugging.
 
Methods inherited from class com.mckoi.database.interpret.Statement
addTable, Debug, init, resolveTree, resolveVariableName
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Select

public Select()
Method Detail

prepare

public void prepare()
             throws DatabaseException
Prepares the select statement with a Database object. This sets up internal state so that it correctly maps to a database. Also, this checks format to ensure there are no run-time syntax problems. This must be called because we 'evaluate' the statement.

NOTE: Care must be taken to ensure that all methods called here are safe in as far as modifications to the data occuring. The rules for safety should be as follows. If the database is in EXCLUSIVE mode, then we need to wait until it's switched back to SHARED mode before this method is called. All collection of information done here should not involve any table state info. except for column count, column names, column types, etc. Queries such as obtaining the row count, selectable scheme information, and certainly 'getCellContents' must never be called during prepare. When prepare finishes, the affected tables are locked and the query ia safe to 'evaluate' at which time table state is safe to inspect.

Specified by:
prepare in class Statement
Throws:
DatabaseException

evaluate

public Table evaluate()
               throws DatabaseException
Evaluates the select statement with the given Database context.

Specified by:
evaluate in class Statement
Throws:
DatabaseException

toString

public java.lang.String toString()
Outputs information for debugging.

Overrides:
toString in class java.lang.Object