com.mckoi.database.interpret

Class Select

java.lang.Object

com.mckoi.database.interpret.Statement

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

Constructors

Constructor and Description
Select()

Method Summary

Modifier and Type	Method and Description
Table	evaluate() Evaluates the select statement with the given Database context.
void	prepare() Prepares the select statement with a Database object.
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 String toString()

Outputs information for debugging.

Overrides:

toString in class Object