The following SQL Statements can be used only in routines.

<handler declaration>

<assignment statement>

<compound statement>

<case statement>

<if statement>

<while statement>

<repeat statement>

<for statement>

<loop statement>

<iterate statement

<leave statement>

<signal statement>

<resignal statement>

<return statement>

<select statement: single row>

The following SQL Statements can be used in procedures but not in functions.

<call statement>

<delete statement>

<insert statement>

<update statement>

<merge statement>

As shown in the examples below, the formal parameters and the variables of the routine can be used in statements, similar to the way a column reference is used.

A compound statement is enclosed in a BEGIN / END block with optional labels. It can contain one or more <SQL variable declaration>, <declare cursor> or <handler declaration> before at least one SQL statement. The BNF is given below:

<compound statement> ::= [ <beginning label> <colon> ] BEGIN [[NOT] ATOMIC]

[{<SQL variable declaration> <semicolon>} ...]

[{<declare cursor> <semicolon>} ...]

[{<handler declaration> <semicolon>}...]

{<SQL procedure statement> <semicolon>} ...

END [ <ending label> ]

An example of a simple compound statement body is given below. It performs the common task of inserting related data into two table. The IDENTITY value that is automatically inserted in the first table is retrieved using the IDENTITY() function and inserted into the second table.

CREATE PROCEDURE new_customer(firstname VARCHAR(50), lastname  VARCHAR(50), address VARCHAR(100))
  MODIFIES SQL DATA
    BEGIN ATOMIC
    INSERT INTO customers VALUES (DEFAULT, firstname, lastname, CURRENT_TIMESTAMP);
    INSERT INTO addresses VALUES (DEFAULT, IDENTITY(), address);
  END

A <variable declaration> defines the name and data type of the variable and, optionally, its default value. In the next example, a variable is used to hold the IDENTITY value. In addition, the formal parameters of the procedure are identified as input parameters with the use of the optional IN keyword. This procedure does exactly the same job as the procedure in the previous example.

CREATE PROCEDURE new_customer(IN firstname VARCHAR(50), IN lastname VARCHAR(50), IN address VARCHAR(100))
  MODIFIES SQL DATA
  BEGIN ATOMIC
    DECLARE temp_id INTEGER;
    INSERT INTO CUSTOMERS VALUES (DEFAULT, firstname, lastname, CURRENT_TIMESTAMP);
    SET temp_id = IDENTITY();
    INSERT INTO ADDRESSES VALUES (DEFAULT, temp_id, address);
  END

The BNF for variable declaration is given below:

DECLARE variable

SQL variable declaration

<SQL variable declaration> ::= DECLARE <variable name list> <data type> [DEFAULT <default value>]

<variable name list> ::= <variable name> [ { <comma> <variable name> }... ]

Examples of variable declaration are given below. Note that in a DECLARE statement with multiple comma-separated variable names, the type and the default value applies to all the variables in the list:

  BEGIN ATOMIC
    DECLARE temp_zero DATE;
    DECLARE temp_one, temp_two INTEGER DEFAULT 2;
    DECLARE temp_three VARCHAR(20) DEFAULT 'no name';
    -- more statements ...
    SET temp_zero = DATE '2010-03-18';
    SET temp_two = 5;
    -- more statements ...
  END

A <declare cursor> statement is used to declare a SELECT statement. The current usage of this statement in early versions of HyperSQL 2.0 is exclusively to return a result set from a procedure. The result set is returned to the JDBC CallableStatement object that calls the procedure. The getResultSet() method of CallableStatement is then used to retrieve the JDBC ResultSet.

In the <routine definition>, the DYNAMIC RESULT SETS clause must be used to specify a value above zero. The DECLARE CURSOR statement is used after any variable declaration in compound statement block. The <open statement> is then executed for the cursor at the point where the result set should be populated.

After the procedure is executed with a JDBC CallableStatement execute() method, all the result sets that were opened are returned to the JDBC CallableStatement.

Calling getResultSet() will return the first ResultSet. When there are multiple result sets, the getMoreResults() method of the Callable statement is called to move to the next ResultSet, before getResultSet() is called to return the next ResultSet. See the Data Access and Change chapter on the syntax for declaring the cursor.

  BEGIN ATOMIC
    DECLARE temp_zero DATE;
    DECLARE result CURSOR FOR SELECT * FROM INFORMATION_SCHEMA.TABLES WITH RETURN;
    -- more statements ...
    OPEN result;
  END

A <handler declaration> defines the course of action when an exception or warning is raised during the execution of the compound statement. A compound statement may have one or more handler declarations. These handlers become active when code execution enters the compound statement block and remain active in any sub-block and statement within the block. The handlers become inactive when code execution leaves the block.

In the previous example, if an exception is thrown during the execution of either SQL statement, the execution of the compound statement is terminated and the exception is propagated and thrown by the CALL statement for the procedure. A handler declaration can resolve the thrown exception within the compound statement without propagating it, and allow the execution of the <compound statement> to continue.

In the example below, the UNDO handler declaration catches any exception that is thrown during the execution of the compound statement inside the BEGIN / END block. As it is an UNDO handler, all the changes to data performed within the compound statement (BEGIN / END) block are rolled back. The procedure then returns without throwing an exception.

CREATE PROCEDURE NEW_CUSTOMER(IN firstname VARCHAR(50), IN lastname VARCHAR(50), IN address VARCHAR(100))
    MODIFIES SQL DATA
  label_one: BEGIN ATOMIC
    DECLARE temp_id INTEGER;
    DECLARE UNDO HANDLER FOR SQLEXCEPTION LEAVE label_one;
    INSERT INTO CUSTOMERS VALUES (DEFAULT, firstname, lastname, CURRENT_TIMESTAMP);
    SET temp_id = IDENTITY();
    INSERT INTO ADDRESSES VALUES (DEFAULT, temp_id, address);
  END

Other types of hander are CONTINUE and EXIT handlers. A CONTINUE handler ignores any exception and proceeds to the next statement in the block. An EXIT handler terminates execution without undoing the data changes performed by the previous (successful) statements.

The conditions can be general conditions, or specific conditions. Among general conditions that can be specified, SQLEXCEPTION covers all exceptions, SQLWARNING covers all warnings, while NOT FOUND covers the not-found condition, which is raised when a DELETE, UPDATE, INSERT or MERGE statement completes without actually affecting any row. Alternatively, one or more specific conditions can be specified (separated with commas) which apply to specific exceptions or warnings or classes or exceptions or warnings. A specific condition is specified with SQLSTATE <value>, for example SQLSTATE 'W_01003' specifies the warning raised after a SQL statement is executed which contains an aggregate function which encounters a null value during execution. An example is given below which activates the handler when either of the two warnings is raised:

DECLARE UNDO HANDLER FOR SQLSTATE 'W_01003', 'W_01004' LEAVE label_one;

The BNF for <handler declaration> is given below:

DECLARE HANDLER

declare handler statement

<handler declaration> ::= DECLARE {UNDO | CONTINUE | EXIT} HANDLER FOR {SQLEXCEPTION | SQLWARNING | NOT FOUND} | { SQL_STATE <state value> [, ...]} [<SQL procedure statement>];

A handler declaration may specify an SQL procedure statement to be performed when the handler is activated. When an exception occurs, the example below performs the UNDO as in the previous example, then inserts the (invalid) data into a separate table.

DECLARE UNDO HANDLER FOR SQLEXCEPTION
    INSERT INTO invalid_customers VALUES(firstanme, lastname, address);

The <SQL procedure statement> is required by the SQL Standard but is optional in HyperSQL. If the execution of the <SQL procedure statement> specified in the handler declaration throws an exception itself, then it is handled by the handlers that are currently active. The <SQL procedure statement> can itself be a compound statement with its own handlers.

The SET statement is used for assignment. It can be used flexibly with rows or single values. The BNF is given below:

<assignment statement> ::= <singleton variable assignment> | <multiple variable assignment>

<singleton variable assignment> ::= SET <assignment target> <equals operator> <assignment source>

<multiple variable assignment> ::= SET (<variable or parameter>, ...) = <row value expression>

In the example below, the result of the SELECT is assigned to two OUT or INOUT arguments. The SELECT must return one row. If it returns more than one, an exception is raised. If it returns no row, no change is made to ARG1 and ARG2.

SET (arg1, arg2) = (SELECT col1, col2 FROM atable WHERE id = 10);

In the example below, the result of a function call is assigned to VAR1.

SET var1 = SQRT(var2);

A special form of SELECT can also be used for assigning values from a query to one or more arguments or variables. This works similar to a SET statement that has a SELECT statement as the source.

SELECT : SINGLE ROW

select statement: single row

<select statement: single row> ::= SELECT [ <set quantifier> ] <select list> INTO <select target list> <table expression>

<select target list> ::= <target specification> [ { <comma> <target specification> }... ]

Retrieve values from a specified row of a table and assign the fields to the specified targets. The example below has an identical effect to the example of SET statement given above.

SELECT col1, col2 INTO arg1, arg2 FROM atable WHERE id = 10;

Each parameter of a procedure can be defined as IN, OUT or INOUT. An IN parameter is an input to the procedure and is passed by value. The value cannot be modified inside the procedure body. An OUT parameter is a reference for output. An INOUT parameter is a reference for both input and output. An OUT or INOUT parameter argument is passed by reference, therefore only a dynamic parameter argument or a variable within an enclosing procedure can be passed for it. The assignment statement is used to assign a value to an OUT or INOUT parameter.

In the example below, the procedure is declared with an OUT parameter.

CREATE PROCEDURE new_customer(OUT newid INT, IN firstname VARCHAR(50), IN lastname VARCHAR(50), IN address VARCHAR(100))
  MODIFIES SQL DATA
  BEGIN ATOMIC
    DECLARE temp_id INTEGER;
    INSERT INTO CUSTOMERS VALUES (DEFAULT, firstname, lastname, CURRENT_TIMESTAMP);
    SET temp_id = IDENTITY();
    INSERT INTO ADDRESSES VALUES (DEFAULT, temp_id, address);
    SET newid = temp_id;
  END

In the SQL session, or in the body of another stored procedure, a variable must be assigned to the OUT parameter. After the procedure call, this variable will hold the new identity value that was generated inside the procedure.

In the example below, a session variable, the_new_id is declared. After the call to new_customer, the value for the identity is stored in the_new_id variable. This is returned via the next CALL statement. Alternatively, the_new_id can be used as an argument to another CALL statement.

DECLARE the_new_id INT DEFAULT NULL;
CALL new_customer(the_new_id, 'John', 'Smith', '10 Parliament Square'); 
CALL the_new_id;

Various iterated statements can be used in routines. In these statements, the <SQL statement list> consists of one or more SQL statements. The <search condition> can be any valid SQL expression of BOOLEAN type.

<loop statement> ::= [ <beginning label> <colon> ] LOOP <SQL statement list> END LOOP [ <ending label> ]

<while statement> ::= [ <beginning label> <colon> ] WHILE <search condition> DO <SQL statement list> END WHILE [ <ending label> ]

<repeat statement> ::= [ <beginning label> <colon> ]

REPEAT <SQL statement list> UNTIL <search condition> END REPEAT [ <ending label>

In the example below, a multiple rows are inserted into a table in a WHILE loop:

loop_label: WHILE my_var > 0 DO
  INSERT INTO CUSTOMERS VALUES (DEFAULT, my_var);
  SET my_var = my_var - 1;
  IF my_var = 10 THEN SET my_var = 8; END IF;
  IF my_var = 22 THEN LEAVE loop_label; END IF;
END WHILE loop_label;

There are two types of CASE ... WHEN statement and the IF ... THEN statement.

CASE WHEN

case when statement

The simple case statement uses a <case operand> as the predicand of one or more predicates. For the right part of each predicate, it specifies one or more SQL statements to execute if the predicate evaluates TRUE. If the ELSE clause is not specified, at least one of the search conditions must be true, otherwise an exception is raised.

<simple case statement> ::= CASE <case operand> <simple case statement when clause>... [ <case statement else clause> ] END CASE

<simple case statement when clause> ::= WHEN <when operand list> THEN <SQL statement list>

<case statement else clause> ::= ELSE <SQL statement list>

A skeletal example is given below. The variable var_one is first tested for equality with 22 or 23 and if the test evaluates to TRUE, then the INSERT statement is performed and the statement ends. If the test does not evaluate to TRUE, the next condition test, which is an IN predicate, is performed with var_one and so on. The statement after the ELSE clause is performed if none the previous tests returns TRUE.

CASE var_one
  WHEN 22, 23 THEN INSERT INTO t_one ...;
  WHEN IN (2, 4, 5) THEN DELETE FROM t_one WHERE ...;
  ELSE UPDATE t_one ...;
  END CASE

The searched case statement uses one or more search conditions, and for each search condition, it specifies one or more SQL statements to execute if the search condition evaluates TRUE. An exception is raised if there is no ELSE clause and none of the search conditions evaluates TRUE.

<searched case statement> ::= CASE <searched case statement when clause>... [ <case statement else clause> ] END CASE

<searched case statement when clause> ::= WHEN <search condition> THEN <SQL statement list>

The example below is partly a rewrite of the previous example, but a new condition is added:

CASE WHEN var_one = 22 OR var_one = 23 THEN INSERT INTO t_one ...;
  WHEN var_one IN (2, 4, 5) THEN DELETE FROM t_one WHERE ...;
  WHEN var_two IS NULL THEN UPDATE t_one ...;
  ELSE UPDATE t_one ...;
  END CASE

IF

if statement

The if statement is very similar to the searched case statement. The difference is that no exception is raised if there is no ELSE clause and no search condition evaluates TRUE.

<if statement> ::= IF <search condition> <if statement then clause> [ <if statement elseif clause>... ] [ <if statement else clause> ] END IF

<if statement then clause> ::= THEN <SQL statement list>

<if statement elseif clause> ::= ELSEIF <search condition> THEN <SQL statement list>

<if statement else clause> ::= ELSE <SQL statement list>

The RETURN statement is required and used only in functions. The body of a function is either a RETURN statement, or a compound statement that contains a RETURN statement.

RETURN

return statement

<return statement> ::= RETURN <return value>

<return value> ::= <value expression> | NULL

Return a value from an SQL function. If the function is defined as RETURNS TABLE, then the value is a TABLE expression such as RETURN TABLE(SELECT ...) otherwise, the value expression can be any scalar expression. In the examples below, the same function is written with or without a BEGIN END block. In both versions, the RETURN value is a scalar expression.

CREATE FUNCTION an_hour_before_max (e_type INT)
  RETURNS TIMESTAMP
  RETURN (SELECT MAX(event_time) FROM atable WHERE event_type = e_type) - 1 HOUR

CREATE FUNCTION an_hour_before_max (e_type INT)
  RETURNS TIMESTAMP
  BEGIN ATOMIC
    DECLAR max_event TIMESTAMP;
    SET max_event = SELECT MAX(event_time) FROM atable WHERE event_type = e_type;
    RETURN max_event - 1 HOUR;
  END

In addition to the RETURN statement, the following statements can be used in specific contexts.

ITERATE STATEMENT

The ITERATE statement can be used to cause the next iteration of a labeled iterated statement (a WHILE, REPEAT or LOOP statement). It is similar to the "continue" statement in C and Java.

<iterate statement> ::= ITERATE <statement label>

LEAVE STATEMENT

The LEAVE statement can be used to leave a labeled block. When used in an iterated statement, it is similar to the "break" statement is C and Java. But it can be used in compound statements as well.

<leave statement> ::= LEAVE <statement label>

Signal and Resignal Statements

The SIGNAL statement is used to throw an exception (or force an exception). When invoked, any exception handler for the given exception is in turn invoked. If there is no handler, the exception is propagated to the enclosing context.

<signal statement> ::= SIGNAL SQL_STATE <state value>

The RESIGNAL statement is used to throw an exception from an exception handler’s <SQL procedure statement>, in effect propagating the exception to the enclosing context without further action by the currently active handlers.

<resignal statement> ::= RESIGNAL SQL_STATE <state value>

More than one version of a routine can be created.

For procedures, the different versions must have different parameter counts.  When the procedure is called, the parameter count determines which version is called.

For functions, the different versions can have the same or different parameter counts. When the parameter count of two versions of a function is the same, the type of parameters must be different. The best matching version of the function is called, according to both the parameter count and parameter types.

Two versions of an overloaded function are given below. One version accepts TIMESTAMP while the other accepts TIME arguments.

CREATE FUNCTION an_hour_before_or_now(t TIMESTAMP)
  RETURNS TIMESTAMP
  IF t > CURRENT_TIMESTAMP THEN
    RETURN CURRENT_TIMESTAMP;
  ELSE
    RETURN t - 1 HOUR;
  END IF

CREATE FUNCTION an_hour_before_or_now(t TIME)
  RETURNS TIME
  CASE t
    WHEN > CURRENT_TIME THEN
      RETURN CURRENT_TIME;
    WHEN >= TIME'01:00:00' THEN
      RETURN t - 1 HOUR;
    ELSE
      RETURN CURRENT_TIME;
  END CASE

more ..

The OUT or INOUT parameters of a PROCEDURE are used to assign simple values to dynamic parameters or to variables in the calling context.

The return value of a FUNCTION can be assigned to a variable, or used inside an SQL statement.

According to the Standard, a SQL/PSM procedure may also return result sets to the calling context. These result sets are dynamic in the sense that a procedure may return a different number of result sets or none at all in different invocations. The SQL Standard uses a mechanism called CURSORS for accessing and modifying rows of a result set one by one. This mechanism is necessary when the database is accessed from an external application program. The JDBC ResultSet interface allows this method of access from Java programs and is supported by HyperSQL.

The SQL Standard uses cursors within the body of a procedure to return result sets. It specifies a somewhat complex mechanism to allow access to these cursors from the calling contexts. HyperSQL does not support access to such result sets within a calling SQL/PSM procedure. This is considered redundant as all operations on data can be performed with non-cursor SQL statements.

The initial releases of HyperSQL support this method of returning single or multiple result sets from SQL/PSM procedures only via the JDBC CallableStatement interface. Cursors are declared and opened within the body of the procedure. No further operation is performed on the cursors within the procedure. When the execution of the procedure is complete, the cursors become available as Java ResultSet objects via the CallableStatement instance that called the SQL/PSM procedure.

An SQL/PSM function or an SQL/JRT function can return a single result when the function is defined as RETURNS TABLE ( .. )

To return a table from a SELECT statement, you should use a return statement such as RETURN TABLE( SELECT ...) in an SQL/PSM function. For an SQL/JRT function, the Java method should return a JDBCResultSet instance.

The JDBC CallableStatement class is used with the SQL statement CALL <routine name> ( <argument 1>, ... ) to call both functions and procedures. The getXXX() methods can be used to retrieve INOUT or OUT arguments after the call. The getResultSet() call can be used to access the ResultSet returned from a function that returns a result set.

If two versions of the same SQL invoked routine with different parameter types are required, they can be defined to point to the same method name or different method names, or even methods in different classes. In the example below, the first two definitions refer to the same method name in the same class. In the Java class, the two static methods are defined with corresponding method signatures.

In the third example, the Java function returns a result set and the SQL declaration includes RETURNS TABLE.

CREATE FUNCTION an_hour_before_or_now(t TIME)
  RETURNS TIME
  NO SQL
  LANGUAGE JAVA PARAMETER STYLE JAVA
  EXTERNAL NAME 'CLASSPATH:org.npo.lib.nowLessAnHour'

CREATE FUNCTION an_hour_before_or_now(t TIMESTAMP)
  RETURNS TIMESTAMP
  NO SQL
  LANGUAGE JAVA PARAMETER STYLE JAVA
  EXTERNAL NAME 'CLASSPATH:org.npo.lib.nowLessAnHour'

CREATE FUNCTION testquery(INTEGER) 
  RETURNS TABLE(n VARCHAR(20), i INT) 
  READS SQL DATA
  LANGUAGE JAVA
  EXTERNAL NAME 'CLASSPATH:org.hsqldb.test.TestJavaFunctions.getQueryResult'

In the Java class:

    public static java.sql.Time nowLessAnHour(java.sql.Time value) {
        ...
    }
    public static java.sql.Timestamp nowLessAnHour(java.sql.Timestamp value)
        ...
    }

    public static ResultSet getQueryResult(Connection connection, int i) throws SQLException {
        Statement st = connection.createStatement();
        return st.executeQuery("SELECT * FROM T WHERE I < " + i);
    }

Java procedures are defined similarly to functions. The differences are:

An example of a procedure definition is given below:

CREATE PROCEDURE new_customer(firstname VARCHAR(50), lastname  VARCHAR(50), address VARCHAR(100))
  MODIFIES SQL DATA
  LANGUAGE JAVA
  EXTERNAL NAME 'CLASSPATH:org.hsqldb.test.Test01.newCustomerProcedure'

The static methods that are used for procedures and functions must be declared in a public class. The methods must be declared as public static. For functions, the method return type must be one of the JDBC supported types. The IN parameters of the method must be declared as one of the supported types. The OUT and INOUT parameters must be declared as Java arrays of supported types. If the SQL definition of a function includes RETURNS NULL ON NULL INPUT, then the IN parameters of the Java static function can be int or long primitives, otherwise, they must be Integer or Long. The declared Java arrays for OUT and INOUT parameters for SQL INTEGER or BIGINT must be Integer[] or Long[] respectively.

If the SQL definition of the routine includes NO SQL, then no JDBC method call is allowed to execute in the method body. Otherwise, a JDBC Connection can be used within the Java method to access the database. If the definition includes CONTAINS SQL, then no table data can be read. If the definition includes READS SQL DATA, then no table data can be modified. If the definition includes MODIFIES SQL DATA, then data can be modified. In all modes, it is not allowed to execute DDL statements that change the schema definition.

It is possible to use DECLARE LOCAL TEMPORARY TABLE in a Java method, as this is in the session scope.

There are two ways to use the JDBC Connection object.

Both methods return a connection that is based on the current session. This connection has some extra properties, for example, the Close() method does not actually close it.

An example of an SQL PROCEDURE with its Java method definition is given below. The CREATE PROCEDURE statement is the same with or without the Connection parameter:

CREATE PROCEDURE proc1(IN P1 INT, IN P2 INT, OUT P3 INT)
SPECIFIC P2 LANGUAGE JAVA DETERMINISTIC MODIFIES SQL DATA EXTERNAL NAME 'CLASSPATH:org.hsqldb.test.TestStoredProcedure.procTest2'");

In the first example, the "jdbc:default:connection" method is used. In the second example, a connection parameter is used

    public static void procTest2(int p1, int p2,
                       Integer[] p3) throws java.sql.SQLException {

        Connection conn =
            DriverManager.getConnection("jdbc:default:connection");
        java.sql.Statement stmt = conn.createStatement();

        stmt.execute("INSERT INTO MYTABLE VALUES(" + p1 + ",'test1')");
        stmt.execute("INSERT INTO MYTABLE VALUES(" + p2 + ",'test2')");

        java.sql.ResultSet rs = stmt.executeQuery("select * from MYTABLE");
        java.sql.ResultSetMetaData meta = rs.getMetaData();

        int cols  = meta.getColumnCount();
        p3[0] = Integer.valueOf(cols);

        rs.close();
        stmt.close();
    }

//  alternative declaration with Connection parameter
//  public static void procTest2(Connection conn, int p1, int p2,
//                    Integer[] p3) throws java.sql.SQLException {

When the stored procedure is called by the user's program, the value of the OUT parameter can be read after the call.

    // a CallableStatement is used to prepare the call
    // the OUT parameter contains the return value
    CallableStatement c = conn.prepareCall("call proc1(1,2,?)");
    c.execute();
    int value = c.getInt(1);

The legacy HyperSQL statement, CREATE ALIAS <name> FOR <fully qualified Java method name> is no longer supported directly. It is supported when importing databases and translates to a special CREATE FUNCTION <name> statement that creates the function in the PUBLIC schema.

The direct use of a Java method as a function is still supported but deprecated. It is internally translated to a special CREATE FUNCTION statement where the name of the function is the double quoted, fully qualified name of the Java method used.

By default, the static methods of any class that is on the classpath are available to be used. This can compromise security in some systems. The optional Java system property hsqldb.method_class_names allows preventing access to classe other than java.lang.Math or specifying a semicolon-separated list of allowed classes. A property value that ends with .* is treated as a wild card and allows access to all classe or method names formed by substitution of the * (asterisk).

In the example below, the property has been included as an argument to the java command.

    java -Dhsqldb.method_class_names="org.me.MyClass;org.you.YourClass;org.you.lib.*" [the rest of the command line]

The above example allows access to the methods in the two classes: org.me.MyClass and org.you.YourClass together with all the classes in the org.you.lib package. Note that if the property is not defined, no access control is performed at this level.

Once the routine has been defined, the normal database access control still applies. The routine can be executed only by the users who have been granted EXECUTE privileges on it. The user who executes a Java routine must also have the relevant access privileges on the tables that are used inside the Java method.

An aggregate function is always defined with 4 parameters. The first parameter is the parameter that is used when the function is invoked in SQL statements, the rest of the parameter are invisible to the invoking SQL statement. The type of the first parameter is user defined. The type of the second parameter must be BOOLEAN. The third and fourth parameters have user defined types and must be defined as INOUT parameters. The defined return type of the function determines the type of the value returned when the function is invoked.

CREATE AGGREGATE FUNCTION

user defined aggregate function definition

Aggregate function definition is similar to normal function definition and has the mandatory <returns clause>. The BNF is given below.

<user defined aggregate function> ::= CREATE AGGREGATE FUNCTION <schema qualified routine name> <SQL aggregate parameter declaration list> <returns clause> <routine characteristics> <routine body>

The parameter declaration list BNF is given below. The type of the first parameter is used when the function is invoked as part of an SQL statement. When multiple versions of a function are required, each version will have the first parameter of a different type.

<SQL aggregate declaration list> ::= <left paren> [IN] [ <SQL parameter name> ] <parameter type> <comma> [IN] [ <SQL parameter name> ] BOOLEAN <comma> INOUT [ <SQL parameter name> ] <parameter type> <comma> INOUT [ <SQL parameter name> ] <parameter type> <right paren>

The return type is user defined. This is the type of the resulting value when the function is called. Usually an aggregate function is defined with CONTAINS SQL, as it normally does not read the data in database tables, but it is possible to define the function with READS SQL DATA and access the database tables.

When a SQL statement that uses the aggregate function is executred, HyperSQL invokes the aggregate function, with all the arguments set, once per each row in order to compute the values. Finally, it invokes the function once more to return the final result.

In the computation phase, the first argument is the value of the user argument as specified in the SQL statement, computed for the current row. The second argument is the boolean FALSE. The third and fourth argument values can have any type and are initially null, but they can be updated in the body of the function during each invocation. The third and fourth arguments act as registers and hold their values between invocations. The return value of the function is ignored during the computation phase (when the second parameter is FALSE).

After the computation phase, the function is invoked once more to get the final result. In this invocation, the first argument is NULL and the second argument is boolean TRUE. The third and fourth arguments hold the values they held at the end of the last invocation. The value returned by the function in this invocation is used as the result of the aggregate function computation in the invoking SQL statement. In SQL queries with GROUP BY, the call sequence is repeated separately for each separate group.

The example below features a user defined version of the Standard AVG(<value expression>) aggregate function for INTEGER input and output types. This function behaves differently from the Standard AVG function as it returns 0 when all the input values are null.

CREATE AGGREGATE FUNCTION udavg(IN x INTEGER, IN flag BOOLEAN, INOUT addup BIGINT, INOUT counter INT)
  RETURNS INTEGER
  CONTAINS SQL
  BEGIN ATOMIC
    IF flag THEN
      RETURN addup / counter;
    ELSE
      SET counter = COALESCE(counter, 0) + 1;
      SET addup = COALESCE(addup, 0) || COALESCE(x, 0);
      RETURN NULL;
    END IF;
  END

The user defined aggregate function is used in a select statement in the example below. Only the first parameter is visible and utilised in the select statement.

SELECT udavg(id) FROM customers GROUP BY lastname;

In the example below, the function returns an array that contains all the values passed for the aggregated column. For use with longer arrays, you can optimise the function by defining a larger array in the first iteration, and using the TRIM_ARRAY function on the RETURN to cut the array to size. This function is similar to the built-in ARRAY_AGG function

CREATE AGGREGATE FUNCTION array_aggregate(IN val VARCHAR(100), IN flag boolean, INOUT buffer VARCHAR(100) ARRAY, INOUT counter INT)
  RETURNS VARCHAR(100) ARRAY
  CONTAINS SQL
  BEGIN ATOMIC
    IF flag THEN
      RETURN buffer;
    ELSE
      IF val IS NULL THEN RETURN NULL; END IF;
      IF counter IS NULL THEN SET counter = 0; END IF;
      SET counter = counter + 1;
      IF counter = 1 THEN SET buffer = ARRAY[val];
      ELSE SET buffer[counter] = val; END IF;
      RETURN NULL;
    END IF;
  END

The tables and data for the select statement below are created with the DatabaseManager or DatabaseManagerSwing GUI apps. (You can find the SQL in the TestSelf.txt file in the zip). Part of the output is shown. Each row of the output includes an array containing the values for the invoices for each customer.

SELECT ID, FIRSTNAME, LASTNAME, ARRAY_AGGREGATE(CAST(INVOICE.TOTAL AS VARCHAR(100))) 
  FROM customer JOIN INVOICE ON ID =CUSTOMERID
  GROUP BY ID, FIRSTNAME, LASTNAME

11 Susanne   Karsen    ARRAY['3988.20']                               
12 John      Peterson  ARRAY['2903.10','4382.10','4139.70','3316.50'] 
13 Michael   Clancy    ARRAY['6525.30']                               
14 James     King      ARRAY['3665.40','905.10','498.00']             
18 Sylvia    Clancy    ARRAY['634.20','4883.10']                      
20 Bob       Clancy    ARRAY['3414.60','744.60']

In the example below, the function returns a string that contains the comma-separated list of all the values passed for the aggregated column. This function is similar to the built in GROUP_CONCAT function.

CREATE AGGREGATE FUNCTION group_concatenate(IN val VARCHAR(100), IN flag BOOLEAN, INOUT buffer VARCHAR(1000), INOUT counter INT
 RETURNS VARCHAR(1000)
 CONTAINS SQL
 BEGIN ATOMIC
 IF FLAG THEN
  RETURN BUFFER;
 ELSE
  IF val IS NULL THEN RETURN NULL; END IF;
  IF buffer IS NULL THEN SET BUFFER = ''; END IF;
  IF counter IS NULL THEN SET COUNTER = 0; END IF;
  IF counter > 0 THEN SET buffer = buffer || ','; END IF;
  SET buffer = buffer + val;
  SET counter = counter + 1;
  RETURN NULL;
 END IF;
 END

The same tables and data as for the previous example is ued. Part of the output is shown. Each row of the output is a comma-separated list of names.

SELECT group_concatenate(firstname || ' ' || lastname) FROM customer GROUP BY lastname
  
Laura Steel,John Steel,John Steel,Robert Steel                                   
Robert King,Robert King,James King,George King,Julia King,George King            
Robert Sommer,Janet Sommer                                                       
Michael Smith,Anne Smith,Andrew Smith                                            
Bill Fuller,Anne Fuller                                                          
Laura White,Sylvia White                                                         
Susanne Clancy,Michael Clancy,Sylvia Clancy,Bob Clancy,Susanne Clancy,John Clancy

A Java aggregate function is defined similarly to PSM functions, apart from the routine body, which is defined as EXTERNAL NAME ... The Java function signature must follow the rules for both nullable and INOUT parameters, therefore:

No agrument is defined as a primitive or primitive array type. This allows nulls to be passed to the function. The second and third arguments must be defined as arrays of the JDBC non-primitive types listed in the table in the previous section.

In the example below, a user-defined aggregate function for geometric mean is defined.

CREATE AGGREGATE FUNCTION geometric_mean(IN val DOUBLE, IN flag BOOLEAN, INOUT register DOUBLE, INOUT counter INT)
  RETURNS DOUBLE
  NO SQL
  LANGUAGE JAVA
  EXTERNAL NAME 'CLASSPATH:org.hsqldb.test.Test01.geometricMean'

The Java function definition is given below:

    public static Double geometricMean(Double in, Boolean flag,
            Double[] register, Integer[] counter) {
        if (flag) {
            if (register[0] == null) { return null; }
            double a = register[0].doubleValue();
            double b = 1 / (double) counter[0];
            return Double.valueOf(java.lang.Math.pow(a, b));
        }
        if (in == null) { return null; }
        if (in.doubleValue() == 0) { return null; }
        if (register[0] == null) {
            register[0] = in;
            counter[0]  = Integer.valueOf(1);
        } else {
            register[0] = Double.valueOf(register[0].doubleValue() * in.doubleValue());
            counter[0] = Integer.valueOf(counter[0].intValue() + 1);
        }
        return null;
    }

In a select statement, the function is used like built in aggregate functions:

SELECT geometric_mean(age) FROM  FROM customer

The <routine characteristics> clause covers several sub-clauses

<routine characteristics> ::= [ <routine characteristic>... ]

<routine characteristic> ::= <language clause> | <parameter style clause> | SPECIFIC <specific name> | <deterministic characteristic> | <SQL-data access indication> | <null-call clause> | <returned result sets characteristic> | <savepoint level indication>

LANGUAGE

language clause

The <language clause> refers to the language in which the routine body is written. It is either SQL or Java. The default is SQL, so JAVA must be specified for SQL/JRT routines.

<language clause> ::= LANGUAGE <language name>

<language name> ::= SQL | JAVA

The parameter style is not allowed for SQL routines. It is optional for Java routines and, in HyperSQL, the only value allowed is JAVA.

<parameter style> ::= JAVA

SPECIFIC NAME

specific name

The SPECIFIC <specific name> clause is optional but the engine will creates an automatic name if it is not present. When there are several versions of the same routine, the <specific name> is used in schema manipulation statements to drop or alter a specific version. The <specific name> is a user-defined name. It applies to both functions and procedures. In the examples below, a specific name is specified for each function.

CREATE FUNCTION an_hour_before_or_now(t TIMESTAMP)
  RETURNS TIMESTAMP
  NO SQL
  LANGUAGE JAVA PARAMETER STYLE JAVA
  SPECIFIC an_hour_before_or_now_with_timestamp
  EXTERNAL NAME 'CLASSPATH:org.npo.lib.nowLessAnHour'

CREATE FUNCTION an_hour_before_max (e_type INT)
  RETURNS TIMESTAMP SPECIFIC an_hour_before_max_with_int
  RETURN (SELECT MAX(event_time) FROM atable WHERE event_type = e_type) - 1 HOUR

DETERMINISTIC

deterministic characteristic

The <deterministic characteristic> clause indicates that a routine is deterministic or not. Deterministic means the routine does not reference random values, external variables, or time of invocation. The default is NOT DETERMINISTIC. It is essential to declare this characteristics correctly for an SQL/JRT routine, as the engine does not know the contents of the Java code, which could include calls to methods returning random or time sensitive values.

<deterministic characteristic> ::= DETERMINISTIC | NOT DETERMINISTIC

SQL DATA access

SQL DATA access characteristic

The <SQL-data access indication>  clause indicates the extent to which a routine interacts with the database or the data stored in the database tables (SQL data).  NO SQL means no SQL command is issued in the routine body and can be used only for SQL/JRT functions. CONTAINS SQL means some SQL commands are used, but they do not read or modify the SQL data. READS SQL DATA and MODIFIES SQL DATA are self explanatory.

<SQL-data access indication> ::= NO SQL | CONTAINS SQL | READS SQL DATA | MODIFIES SQL DATA

NULL INPUT

null call clause

Null Arguments

The <null-call clause> is used only for functions. If a function returns NULL when any of the calling arguments is null, then by specifying RETURNS NULL ON NULL INPUT, calls to the function are known to be redundant and do not take place when an argument is null. This simplifies the coding of the SQL/JRT Java methods and improves performance at the same time.

<null-call clause> ::= RETURNS NULL ON NULL INPUT | CALLED ON NULL INPUT

SAVEPOINT LEVEL

transaction impact

The <savepoint level indication> is used only for procedures and refers to the visibility of existing savepoints within the body of the procedure. If NEW SAVEPOINT LEVEL is specified, savepoints that have been declared prior to calling the procedure become invisible within the body of the procedure. HyperSQL’s implementation accepts only NEW SAVEPOINT LEVEL, which must be specified.

<savepoint level indication> ::= NEW SAVEPOINT LEVEL | OLD SAVEPOINT LEVEL

DYNAMIC RESULT SETS

returned result sets characteristic

The <returned result sets characteristic> is used only for SQL/PSM procedures. The maximum number of result sets that a procedure may return can be specified with the clause below. The default is zero. Details are discussed in the previous sections.

<returned result sets characteristic> ::= DYNAMIC RESULT SETS <maximum returned result sets>