ScanQualifier
GenericQualifier
, GenericScanQualifier
, UTFQualifier
public interface Qualifier
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.
if (qualifier.negateCompareResult()) { compare_result = row[(qualifier.getColumnId())].compare( qualifier.getOperator(), qualifier.getOrderable(), qualifier.getOrderedNulls(), qualifier.getUnknownRV()) if (qualifier.negateCompareResult()) { compare_result = !(compare_result); } }
Qualifiers are often passed through interfaces as a set of Qualifiers, rather than one at a time, for example see the qualifier argument in TransactionController.openScan().
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[3]; // 3 and clauses 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
,
TransactionController.openScan(long, boolean, int, int, int, org.apache.derby.iapi.services.io.FormatableBitSet, org.apache.derby.iapi.types.DataValueDescriptor[], int, org.apache.derby.iapi.store.access.Qualifier[][], org.apache.derby.iapi.types.DataValueDescriptor[], int)
,
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)
Modifier and Type | Field | Description |
---|---|---|
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.
|
Modifier and Type | Method | Description |
---|---|---|
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.
|
static final int VARIANT
NOTE: the following is guaranteed: VARIANT < SCAN_INVARIANT < QUERY_INVARIANT < CONSTANT
static final int SCAN_INVARIANT
static final int QUERY_INVARIANT
static final int CONSTANT
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.
DataValueDescriptor getOrderable() throws StandardException
StandardException
- Thrown on errorint getOperator()
boolean negateCompareResult()
boolean getOrderedNulls()
boolean getUnknownRV()
void clearOrderableCache()
void reinitialize()
Apache Derby V10.14 Internals - Copyright © 2004,2018 The Apache Software Foundation. All Rights Reserved.