uk.ac.ed.epcc.webapp.jdbc.expr

Interface GroupingSQLValue<T>

Type Parameters:

T - type of SQLValue

All Superinterfaces:

SQLValue<T>, Targetted<T>

All Known Subinterfaces:

DateSQLExpression, FieldSQLExpression<T,X>, FieldValue<T,X>, NestedSQLValue<T,N>, SQLAccessor<T,R>, SQLExpression<T>, WrappedSQLExpression<T>

All Known Implementing Classes:

AbstractSelfSQLValue, AliasSQLValue, ArrayFuncExpression, BinaryExpression, BinarySQLValue, BooleanFieldExpression, CaseExpression, CastDoubleSQLExpression, CastLongSQLExpression, CompareSQLExpression, CompositeIndexedSQLValue, ConcatSQLExpression, ConstExpression, ConstIndexedSQLValue, CountDistinctExpression, DateDerefSQLExpression, DateFieldExpression, DateSQLValue, DerefSQLExpression, DistinctCountSQLValue, DoubleConvertSQLValue, DurationConvertSQLValue, DurationFieldValue, DurationSecondConvertSQLValue, DurationSQLExpression, FieldExpression, FuncExpression, IndexedFieldValue, IntConvertSQLValue, LabellerSQLValue, LengthExpression, LocateSQLExpression, LongConvertSQLValue, MillisecondSQLValue, MysqlDateConverter, MysqlMillisecondConverter, MysqlSQLHashExpression, MysqlTimestampDiffExpr, NumberFieldExpression, PostgresqlDateConverter, PostgresqlMillisecondConverter, RemoteSQLValue, RoundSQLExpression, SelfIdExpression, SelfSQLValue, SQLSelectValue, SQLValuePatternTransform, StreamDataFieldExpression, StringConvertSQLExpression, StringConvertSQLValue, StringFieldExpression, TimestampDateFieldExpression, TupleSelfSQLValue, TypeConverterSQLValue, TypeFilterProducerSQLValue, TypeProducerFieldValue

public interface GroupingSQLValue<T>
extends SQLValue<T>

A variant of SQLValue which is legal to use for group-by clauses. This allows the class to generate an alternative SQL fragment. This allows complex transformations that do not change the grouping result to be optimised. Not all SQLValues can be used to implement a group-by so this interface needs to be implemented explicitly though there is a default implementation that works for most simple cases. If the SQL representation of the SQLValue is a literal constant it is required to implement this to suppress the group-by clause as literal constants are illegal in group-by clauses but won't actually change the grouping.

See Also:

SQLGroupMapper

Method Summary

Modifier and Type	Method and Description
default int	addGroup(java.lang.StringBuilder sb, boolean qualify) Add the group-by clause to a query.
default boolean	checkContentsCanGroup() return false if this instance is not able to perform grouping.
default java.util.List<PatternArgument>	getGroupParameters(java.util.List<PatternArgument> list) Get the parameters for a group-by clause.
default boolean	groupingIsomorphic() Is there always a one-to-one mapping between groups and values

Methods inherited from interface uk.ac.ed.epcc.webapp.jdbc.expr.SQLValue

add, getParameters, getRequiredFilter, makeObject

Methods inherited from interface uk.ac.ed.epcc.webapp.Targetted

getTarget

Method Detail

addGroup

default int addGroup(java.lang.StringBuilder sb,
                     boolean qualify)

Add the group-by clause to a query. Note this can be a null operation in which case it will return zero.

Parameters:

sb -

qualify -

Returns:

actual number of fields added

Throws:

CannotGroupException

getGroupParameters

default java.util.List<PatternArgument> getGroupParameters(java.util.List<PatternArgument> list)

Get the parameters for a group-by clause.

Parameters:

list -

Returns:

modified list

checkContentsCanGroup

default boolean checkContentsCanGroup()

return false if this instance is not able to perform grouping.

Returns:

groupingIsomorphic

default boolean groupingIsomorphic()

Is there always a one-to-one mapping between groups and values

Returns: