Package org.h2.api
Interface AggregateFunction
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public interface AggregateFunction
A user-defined aggregate function needs to implement this interface. The class must be public and must have a public non-argument constructor.Please note this interface only has limited support for data types. If you need data types that don't have a corresponding SQL type (for example GEOMETRY), then use the
Aggregate
interface.
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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.java.lang.Object
getResult()
This method returns the computed aggregate value.int
getType(int[] inputTypes)
This method must return the SQL type of the method, given the SQL type of the input data.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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getType
int getType(int[] inputTypes) throws java.sql.SQLException
This method must return the SQL type of the method, given the SQL 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 SQL type of the parameters,Types
- Returns:
- the SQL type of the result
- Throws:
java.sql.SQLException
- on failure
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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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