org.apache.derby.iapi.store.access
Interface Qualifier

All Known Subinterfaces:
ScanQualifier
All Known Implementing Classes:
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
  

See Also:
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)

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

VARIANT

static final int VARIANT
The DataValueDescriptor can be 1 of 4 types:

NOTE: the following is guaranteed: VARIANT < SCAN_INVARIANT < QUERY_INVARIANT < CONSTANT

See Also:
Constant Field Values

SCAN_INVARIANT

static final int SCAN_INVARIANT
See Also:
Constant Field Values

QUERY_INVARIANT

static final int QUERY_INVARIANT
See Also:
Constant Field Values

CONSTANT

static final int CONSTANT
See Also:
Constant Field Values
Method Detail

getColumnId

int getColumnId()
Get the (zero based) id of the column to be qualified.

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.


getOrderable

DataValueDescriptor getOrderable()
                                 throws StandardException
Get the value that the column is to be compared to.

Throws:
StandardException - Thrown on error

getOperator

int getOperator()
Get the operator to use in the comparison.

See Also:
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)

negateCompareResult

boolean negateCompareResult()
Determine if the result from the compare operation should be negated. If true then only rows which fail the compare operation will qualify.

See Also:
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)

getOrderedNulls

boolean getOrderedNulls()
Get the getOrderedNulls argument to use in the comparison.

See Also:
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)

getUnknownRV

boolean getUnknownRV()
Get the getOrderedNulls argument to use in the comparison.

See Also:
DataValueDescriptor.compare(org.apache.derby.iapi.types.DataValueDescriptor)

clearOrderableCache

void clearOrderableCache()
Clear the DataValueDescriptor cache, if one exists. (The DataValueDescriptor can be 1 of 3 types: o VARIANT - cannot be cached as its value can vary within a scan o SCAN_INVARIANT - can be cached within a scan as its value will not change within a scan o QUERY_INVARIANT- can be cached across the life of the query as its value will never change


reinitialize

void reinitialize()
This method reinitializes all the state of the Qualifier. It is used to distinguish between resetting something that is query invariant and something that is constant over every execution of a query. Basically, clearOrderableCache() will only clear out its cache if it is a VARIANT or SCAN_INVARIANT value. However, each time a query is executed, the QUERY_INVARIANT qualifiers need to be reset.


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