Package com.mckoi.database.interpret
Class Select
- java.lang.Object
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- com.mckoi.database.interpret.Statement
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- com.mckoi.database.interpret.Select
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public class Select extends Statement
Logic for interpreting an SQL SELECT statement.- Author:
- Tobias Downer
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Constructor Summary
Constructors Constructor Description Select()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description 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
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Method Detail
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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 classStatement
- Throws:
DatabaseException
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evaluate
public Table evaluate() throws DatabaseException
Evaluates the select statement with the given Database context.- Specified by:
evaluate
in classStatement
- Throws:
DatabaseException
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toString
public java.lang.String toString()
Outputs information for debugging.- Overrides:
toString
in classjava.lang.Object
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