|
||||||||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
A structure which is used to "qualify" a column. Specifies that the column value in a given column identified by column id is to be compared via a specific operator to a particular DataValueDescriptor value.
The implementation of this interface is provided by the client; the methods of Qualifier are the methods the access code uses to use it.
Arrays of qualifiers are provided to restrict the rows returned by scans. A row is returned from a scan if all qualifications in the array return true.
A qualification returns true if in the following pseudo-code compare_result is true.
} Qualifiers are often passed through interfaces as a set of Qualifiers, rather than one at a time, for example see the qualifier argument inif (qualifier.negateCompareResult()) {}compare_result = row[(qualifier.getColumnId())].compare(if (qualifier.negateCompareResult()) {qualifier.getOperator(), qualifier.getOrderable(), qualifier.getOrderedNulls(), qualifier.getUnknownRV())compare_result = !(compare_result);
To make this consistent the following protocols are to be used when passing
around sets of Qualifiers.
A single dimensional array is to be used to pass around a set of AND'd
qualifiers. Thus qualifier[] argument is to be treated as:
qualifier[0] AND qualifer[1] ... AND qualifier[qualifer.length - 1]
A two dimensional array is to be used to pass around a AND's and OR's in
conjunctive normal form. The top slot of the 2 dimensional array is optimized
for the more frequent where no OR's are present. The first array slot is
always a list of AND's to be treated as described above for single dimensional
AND qualifier arrays. The subsequent slots are to be treated as AND'd arrays
of OR's. Thus the 2 dimensional array qual[][] argument is to be treated as
the following, note if qual.length = 1 then only the first array is valid and
it is and an array of AND clauses:
(qual[0][0] AND qual[0][0] ... AND qual[0][qual[0].length - 1])
AND
(qual[1][0] OR qual[1][1] ... OR qual[1][qual[1].length - 1])
AND
(qual[2][0] OR qual[2][1] ... OR qual[2][qual[2].length - 1])
...
AND
(qual[qual.length - 1][0] OR qual[1][1] ... OR qual[1][2])
If any of the array's qual[0].length ... qual[qual.length -1] are 0 length
they will be evaluated as TRUE; but they must be not NULL. See Example 4 for
encoding of (a or b) that takes advantage of this.
Note that any of the arrays qual[0].length ... qual[qual.length -1] may also
be of length 1, thus no guarantee is made the presence of OR
predicates if qual.length > 1. See example 1a.
The following give pseudo-code examples of building Qualifier arrays:
Example 1: "a AND b AND c"
qualifier = new Qualifier[1][3]; // 3 AND clauses
qualifier[0][0] = a
qualifier[0][1] = b
qualifier[0][2] = c
Example 1a "a AND b AND c" - less efficient than example 1 but legal
qualifier = new Qualifier[3]; // 3 AND clauses
qualifier[0] = new Qualifier[1];
qualifier[1] = new Qualifier[1];
qualifier[2] = new Qualifier[1];
qualifier[0][0] = a
qualifier[1][0] = b
qualifier[2][0] = c
Example 2: "(f) AND (a OR b) AND (c OR d OR e)"
Would be represented by an array that looks like the following:
qualifier = new Qualifier[3]; // 3 and clauses
qualifier[0] = new Qualifier[1]; // to be intitialized to f
qualifier[1] = new Qualifier[2]; // to be initialized to (a OR b)
qualifier[2] = new Qualifier[3]; // to be initialized to (c OR d OR e)
qualifier[0][0] = f
qualifier[1][0] = a
qualifier[1][1] = b
qualifier[2][0] = c
qualifier[2][1] = d
qualifier[2][2] = e
Example 3: "(a OR b) AND (c OR d) AND (e OR f)"
qualifier = new Qualifier[4]; // 4 and clauses
qualifier[0] = new Qualifier[1]; // to be intitialized to TRUE
qualifier[1] = new Qualifier[2]; // to be initialized to (a OR b)
qualifier[2] = new Qualifier[2]; // to be initialized to (c OR d)
qualifier[3] = new Qualifier[2]; // to be initialized to (e OR f)
qualifier[0][0] = TRUE
qualifier[1][0] = a
qualifier[1][1] = b
qualifier[2][0] = c
qualifier[2][1] = d
qualifier[3][0] = e
qualifier[3][1] = f
Example 4: "(a OR b)"
qualifier = new Qualifier[2]; // 2 and clauses
qualifier[0] = new Qualifier[0]; // 0 length array is TRUE
qualifier[1] = new Qualifier[2]; // to be initialized to (a OR b)
qualifier[1][0] = a
qualifier[1][1] = b
,
ScanController
,
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
Field Summary | |
static int |
CONSTANT
|
static int |
QUERY_INVARIANT
|
static int |
SCAN_INVARIANT
|
static int |
VARIANT
The DataValueDescriptor can be 1 of 4 types: VARIANT - cannot be cached as its value can vary within a scan SCAN_INVARIANT - can be cached within a scan as its value will not change within a scan QUERY_INVARIANT- can be cached across the life of the query as its value will never change CONSTANT - can be cached across executions. |
Method Summary | |
void |
clearOrderableCache()
Clear the DataValueDescriptor cache, if one exists. |
int |
getColumnId()
Get the (zero based) id of the column to be qualified. |
int |
getOperator()
Get the operator to use in the comparison. |
DataValueDescriptor |
getOrderable()
Get the value that the column is to be compared to. |
boolean |
getOrderedNulls()
Get the getOrderedNulls argument to use in the comparison. |
boolean |
getUnknownRV()
Get the getOrderedNulls argument to use in the comparison. |
boolean |
negateCompareResult()
Determine if the result from the compare operation should be negated. |
void |
reinitialize()
This method reinitializes all the state of the Qualifier. |
Field Detail |
public static final int VARIANT
NOTE: the following is guaranteed: VARIANT < SCAN_INVARIANT < QUERY_INVARIANT < CONSTANT
public static final int SCAN_INVARIANT
public static final int QUERY_INVARIANT
public static final int CONSTANT
Method Detail |
public int getColumnId()
This id is the column number of the column in the table, no matter whether a partial column set is being retrieved by the actual fetch. Note that the column being specified in the qualifier must appear in the column list being fetched.
public DataValueDescriptor getOrderable() throws StandardException
StandardException
- Thrown on errorpublic int getOperator()
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
public boolean negateCompareResult()
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
public boolean getOrderedNulls()
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
public boolean getUnknownRV()
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
public void clearOrderableCache()
public void reinitialize()
|
Built on Mon 2007-06-04 09:58:47+0400, from revision ??? | |||||||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |