Package org.h2.api
Interface Aggregate
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- All Known Implementing Classes:
UserAggregate.AggregateWrapper
public interface Aggregate
A user-defined aggregate function needs to implement this interface. The class must be public and must have a public non-argument constructor.
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Method Summary
All Methods Instance Methods Abstract Methods Default Methods Modifier and Type Method Description void
add(java.lang.Object value)
This method is called once for each row.int
getInternalType(int[] inputTypes)
This method must return the H2 data type,Value
, of the aggregate function, given the H2 data type of the input data.java.lang.Object
getResult()
This method returns the computed aggregate value.default void
init(java.sql.Connection conn)
This method is called when the aggregate function is used.
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Method Detail
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init
default void init(java.sql.Connection conn) throws java.sql.SQLException
This method is called when the aggregate function is used. A new object is created for each invocation.- Parameters:
conn
- a connection to the database- Throws:
java.sql.SQLException
- on SQL exception
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getInternalType
int getInternalType(int[] inputTypes) throws java.sql.SQLException
This method must return the H2 data type,Value
, of the aggregate function, given the H2 data type of the input data. The method should check here if the number of parameters passed is correct, and if not it should throw an exception.- Parameters:
inputTypes
- the H2 data type of the parameters,- Returns:
- the H2 data type of the result
- Throws:
java.sql.SQLException
- if the number/type of parameters passed is incorrect
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add
void add(java.lang.Object value) throws java.sql.SQLException
This method is called once for each row. If the aggregate function is called with multiple parameters, those are passed as array.- Parameters:
value
- the value(s) for this row- Throws:
java.sql.SQLException
- on failure
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getResult
java.lang.Object getResult() throws java.sql.SQLException
This method returns the computed aggregate value. This method must preserve previously added values and must be able to reevaluate result if more values were added since its previous invocation.- Returns:
- the aggregated value
- Throws:
java.sql.SQLException
- on failure
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