org.apache.derby.iapi.sql.compile
Interface RowOrdering

All Known Implementing Classes:

RowOrderingImpl

public interface RowOrdering

This interface provides a representation of the ordering of rows in a ResultSet.

Field Summary

static int	ASCENDING
static int	DESCENDING
static int	DONTCARE

Method Summary

void	addOrderedColumn(int direction, int tableNumber, int columnNumber) Add a column to this RowOrdering in the current order position.
void	addUnorderedOptimizable(Optimizable optimizable) Add an unordered optimizable to this RowOrdering.
boolean	alwaysOrdered(int tableNumber) Ask whether the given table is always ordered.
void	columnAlwaysOrdered(Optimizable optimizable, int columnNumber) Tell this RowOrdering that it is always ordered on the given column of the given optimizable.
void	copy(RowOrdering copyTo) Copy the contents of this RowOrdering to the given RowOrdering.
boolean	isColumnAlwaysOrdered(int tableNumber, int columnNumber) Return true if the column is always ordered.
void	nextOrderPosition(int direction) Move to the next order position for adding ordered columns.
void	optimizableAlwaysOrdered(Optimizable optimizable) Tell this RowOrdering that it is always ordered on the given optimizable This is useful when considering a unique index where there is an equality match on the entire key - in this case, all the columns are ordered, regardless of the direction or position, or even whether the columns are in the index.
boolean	orderedOnColumn(int direction, int tableNumber, int columnNumber) Tell whether this ordering is ordered on the given column.
boolean	orderedOnColumn(int direction, int orderPosition, int tableNumber, int columnNumber) Tell whether this ordering is ordered on the given column in the given position
void	removeOptimizable(int tableNumber) Tell this row ordering that it is no longer ordered on the given table.

Field Detail

ASCENDING

static final int ASCENDING

See Also:

Constant Field Values

DESCENDING

static final int DESCENDING

See Also:

Constant Field Values

DONTCARE

static final int DONTCARE

See Also:

Constant Field Values

Method Detail

orderedOnColumn

boolean orderedOnColumn(int direction,
                        int orderPosition,
                        int tableNumber,
                        int columnNumber)
                        throws StandardException

Tell whether this ordering is ordered on the given column in the given position

Parameters:

direction - One of ASCENDING, DESCENDING, or DONTCARE depending on the requirements of the caller. An ORDER BY clause cares about direction, while DISTINCT and GROUP BY do not.

orderPosition - The position in the ordering list. For example, for ORDER BY A, B, position 0 has column A, and position 1 has column B. Note that for an ordering, more than one column can be in a single ordering position: for example, in the query SELECT * FROM S, T WHERE S.A = T.B ORDER BY T.B columns S.A and T.B will be in the same ordering positions because they are equal. Also, constant values are considered ordered in all positions (consider SELECT A FROM T WHERE A = 1 ORDER BY A).

tableNumber - The table number of the Optimizable containing the column in question

columnNumber - The column number in the table (one-based).

Returns:

true means this ordering is ordered on the given column in the given position.

Throws:

StandardException - Thrown on error

orderedOnColumn

boolean orderedOnColumn(int direction,
                        int tableNumber,
                        int columnNumber)
                        throws StandardException

Tell whether this ordering is ordered on the given column. This is similar to the method above, but it checks whether the column is ordered in any position, rather than a specified position. This is useful for operations like DISTINCT and GROUP BY.

Parameters:

direction - One of ASCENDING, DESCENDING, or DONTCARE depending on the requirements of the caller. An ORDER BY clause cares about direction, while DISTINCT and GROUP BY do not.

tableNumber - The table number of the Optimizable containing the column in question

columnNumber - The column number in the table (one-based).

Returns:

true means this ordering is ordered on the given column in the given position.

Throws:

StandardException - Thrown on error

addOrderedColumn

void addOrderedColumn(int direction,
                      int tableNumber,
                      int columnNumber)

Add a column to this RowOrdering in the current order position. This is a no-op if there are any unordered optimizables in the join order (see below).

Parameters:

direction - One of ASCENDING, DESCENDING, or DONTCARE. DONTCARE can be used for things like columns with constant value, and for one-row tables.

tableNumber - The table the column is in.

columnNumber - The column number in the table (one-based)

nextOrderPosition

void nextOrderPosition(int direction)

Move to the next order position for adding ordered columns. This is a no-op if there are any unordered optimizables in the join order (see below).

Parameters:

direction - One of ASCENDING, DESCENDING, or DONTCARE. DONTCARE can be used for things like columns with constant value, and for one-row tables.

optimizableAlwaysOrdered

void optimizableAlwaysOrdered(Optimizable optimizable)

Tell this RowOrdering that it is always ordered on the given optimizable This is useful when considering a unique index where there is an equality match on the entire key - in this case, all the columns are ordered, regardless of the direction or position, or even whether the columns are in the index.

Parameters:

optimizable - The table in question

columnAlwaysOrdered

void columnAlwaysOrdered(Optimizable optimizable,
                         int columnNumber)

Tell this RowOrdering that it is always ordered on the given column of the given optimizable. This is useful when a column in the optimizable has an equals comparison with a constant expression or it is involved in a equijoin with an optimizable which is always ordered on the column on which the equijoin is happening. This is reset when the optimizable is removed from this RowOrdering.

Parameters:

optimizable - The table in question

columnNumber - The number of the column in question.

isColumnAlwaysOrdered

boolean isColumnAlwaysOrdered(int tableNumber,
                              int columnNumber)

Return true if the column is always ordered. That will be true if the column has a constant comparison predicate on it or it is involved in a equijoin with an optimizable which is always ordered on the column on which the equijoin is happening.

Parameters:

tableNumber - The table in question

columnNumber - The number of the column in question.

Returns:

true means this column is always ordered

alwaysOrdered

boolean alwaysOrdered(int tableNumber)

Ask whether the given table is always ordered.

removeOptimizable

void removeOptimizable(int tableNumber)

Tell this row ordering that it is no longer ordered on the given table. Also, adjust the current order position, if necessary. This only works to remove ordered columns from the end of the ordering.

Parameters:

tableNumber - The number of the table to remove from this RowOrdering.

addUnorderedOptimizable

void addUnorderedOptimizable(Optimizable optimizable)

Add an unordered optimizable to this RowOrdering. This is to solve the following problem: Suppose we have the query: select * from r, s, t order by r.a, t.b Also suppose there are indexes on r.a and t.b. When the optimizer considers the join order (r, s, t) using the index on r.a, the heap on s, and the index on t.b, the rows from the join order will *NOT* be ordered on t.b, because there is an unordered result set between r and t. So, when s is added to the partial join order, and we then add table t to the join order, we want to ensure that we don't add column t.b to the RowOrdering.

copy

void copy(RowOrdering copyTo)

Copy the contents of this RowOrdering to the given RowOrdering.