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3.9. Procedural Language

3.9.1. Procedural Language
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JBoss Data Virtualization supports a procedural language for defining virtual procedures. These are similar to stored procedures in relational database management systems. You can use this language to define the transformation logic for decomposing INSERT, UPDATE, and DELETE commands against views; these are known as update procedures. See Section 3.10.1, “Virtual Procedures” and Section 3.10.6, “Update Procedures” for more information.

3.9.2. Command Statement
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A command statement executes a DML command, DDL command or dynamic SQL against one or more data sources. See Section 3.5.1, “DML Commands” and Section 3.7.1, “DDL Commands”.
Usage: 
command [(WITH|WITHOUT) RETURN];
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Example 3.8. Example Command Statements

SELECT * FROM MySchema.MyTable WHERE ColA > 100 WITHOUT RETURN;
INSERT INTO MySchema.MyTable (ColA,ColB) VALUES (50, 'hi');
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EXECUTE commands may access IN/OUT, OUT, and RETURN parameters. To access the return value the statement will have the form var = EXEC proc.... To access OUT or IN/OUT values named parameter syntax must be used. For example, EXEC proc(in_param=>'1', out_param=>var) will assign the value of the out parameter to the variable var. It is expected that the data type of parameter will be implicitly convertible to the data type of the variable.
The RETURN clause determines if the result of the command is returnable from the procedure. WITH RETURN is the default. If the command does not return a result set or the procedure does not return a result set, the RETURN clause is ignored. If WITH RETURN is specified, the result set of the command must match the expected result set of the procedure. Only the last successfully executed statement executed WITH RETURN will be returned as the procedure result set. If there are no returnable result sets and the procedure declares that a result set will be returned, then an empty result set is returned.

3.9.3. Dynamic SQL
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Dynamic SQL allows for the execution of an arbitrary SQL command in a virtual procedure. Dynamic SQL is useful in situations where the exact command form is not known prior to execution.
Usage: 
EXECUTE IMMEDIATE <expression> [AS <variable> <type> [, <variable> <type>]* [INTO <variable>]] [USING <variable>=<expression> [,<variable>=<expression>]*] [UPDATE <literal>]
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Syntax Rules:

  • The "AS" clause is used to define the projected symbols names and types returned by the executed SQL string. The "AS" clause symbols will be matched positionally with the symbols returned by the executed SQL string. Non-convertible types or too few columns returned by the executed SQL string will result in an error.
  • The "INTO" clause will project the dynamic SQL into the specified temp table. With the "INTO" clause specified, the dynamic command will actually execute a statement that behaves like an INSERT with a QUERY EXPRESSION. If the dynamic SQL command creates a temporary table with the "INTO" clause, then the "AS" clause is required to define the table's metadata.
  • The "USING" clause allows the dynamic SQL string to contain variable references that are bound at runtime to specified values. This allows for some independence of the SQL string from the surrounding procedure variable names and input names. In the dynamic command "USING" clause, each variable is specified by short name only. However in the dynamic SQL the "USING" variable must be fully qualified to "DVAR.". The "USING" clause is only for values that will be used in the dynamic SQL as legal expressions. It is not possible to use the "USING" clause to replace table names, keywords, etc. This makes using symbols equivalent in power to normal bind (?) expressions in prepared statements. The "USING" clause helps reduce the amount of string manipulation needed. If a reference is made to a USING symbol in the SQL string that is not bound to a value in the "USING" clause, an exception will occur.
  • The "UPDATE" clause is used to specify the updating model count. Accepted values are (0,1,*). 0 is the default value if the clause is not specified. See Section 6.3, “Updating Model Count”.

Example 3.9. Example Dynamic SQL

...
/* Typically complex criteria would be formed based upon inputs to the procedure.
 In this simple example the criteria is references the using clause to isolate
 the SQL string from referencing a value from the procedure directly */
DECLARE string criteria = 'Customer.Accounts.Last = DVARS.LastName';

/* Now we create the desired SQL string */
DECLARE string sql_string = 'SELECT ID, First || '' '' || Last AS Name, Birthdate FROM Customer.Accounts WHERE ' || criteria;

/* The execution of the SQL string will create the #temp table with the columns (ID, Name, Birthdate).
  Note that we also have the USING clause to bind a value to LastName, which is referenced in the criteria. */
EXECUTE IMMEDIATE sql_string AS ID integer, Name string, Birthdate date INTO #temp USING LastName='some name';
/* The temp table can now be used with the values from the Dynamic SQL */
loop on (SELCT ID from #temp) as myCursor
...
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Here is an example showing a more complex approach to building criteria for the dynamic SQL string. In short, the virtual procedure AccountAccess.GetAccounts has inputs ID, LastName, and bday. If a value is specified for ID it will be the only value used in the dynamic SQL criteria. Otherwise if a value is specified for LastName the procedure will detect if the value is a search string. If bday is specified in addition to LastName, it will be used to form compound criteria with LastName.

Example 3.10. Example Dynamic SQL with USING clause and dynamically built criteria string

...
DECLARE string crit = null;
IF (AccountAccess.GetAccounts.ID IS NOT NULL)
 crit = '(Customer.Accounts.ID = DVARS.ID)';
ELSE IF (AccountAccess.GetAccounts.LastName IS NOT NULL)
BEGIN
 IF (AccountAccess.GetAccounts.LastName == '%')
   ERROR "Last name cannot be %";
 ELSE IF (LOCATE('%', AccountAccess.GetAccounts.LastName) < 0)
   crit = '(Customer.Accounts.Last = DVARS.LastName)';
 ELSE
   crit = '(Customer.Accounts.Last LIKE DVARS.LastName)';
 IF (AccountAccess.GetAccounts.bday IS NOT NULL)
   crit = '(' || crit || ' and (Customer.Accounts.Birthdate = DVARS.BirthDay))';
END
ELSE
 ERROR "ID or LastName must be specified.";
EXECUTE IMMEDIATE 'SELECT ID, First || '' '' || Last AS Name, Birthdate FROM Customer.Accounts WHERE ' || crit USING ID=AccountAccess.GetAccounts.ID, LastName=AccountAccess.GetAccounts.LastName, BirthDay=AccountAccess.GetAccounts.Bday;
...
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3.9.4. Dynamic SQL Limitations
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  • The use of dynamic SQL command results in an assignment statement requires the use of a temp table.

    Example 3.11. Example Assignment

    EXECUTE IMMEDIATE <expression> AS x string INTO #temp;
DECLARE string VARIABLES.RESULT = (SELECT x FROM #temp);
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  • The construction of appropriate criteria will be cumbersome if parts of the criteria are not present. For example if "criteria" were already NULL, then the following example results in "criteria" remaining NULL.

    Example 3.12. Example Dangerous NULL handling

    ...
criteria = '(' || criteria || ' and (Customer.Accounts.Birthdate = DVARS.BirthDay))';
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    The preferred approach is for the user to ensure the criteria is not NULL prior its usage. If this is not possible, a good approach is to specify a default as shown in the following example.

    Example 3.13. Example NULL handling

    ...
criteria = '(' || nvl(criteria, '(1 = 1)') || ' and (Customer.Accounts.Birthdate = DVARS.BirthDay))';
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  • If the dynamic SQL is an UPDATE, DELETE, or INSERT command, and the user needs to specify the "AS" clause (which would be the case if the number of rows effected needs to be retrieved). The user will still need to provide a name and type for the return column if the into clause is specified.

    Example 3.14. Example with AS and INTO clauses

    /* This name does not need to match the expected update command symbol "count". */
EXECUTE IMMEDIATE <expression> AS x integer INTO #temp;
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  • Unless used in other parts of the procedure, tables in the dynamic command will not be seen as sources in Teiid Designer.
  • When using the "AS" clause only the type information will be available to Teiid Designer. Result set columns generated from the "AS" clause then will have a default set of properties for length, precision, etc.

3.9.5. Declaration Statement
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A declaration statement declares a variable and its type. After you declare a variable, you can use it in that block within the procedure and any sub-blocks. A variable is initialized to null by default, but can also be assigned the value of an expression as part of the declaration statement.
Usage: 
DECLARE <type> [VARIABLES.]<name> [= <expression>];
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Example Syntax

  • declare integer x;
declare string VARIABLES.myvar = 'value';
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Syntax Rules:

  • You cannot redeclare a variable with a duplicate name in a sub-block
  • The VARIABLES group is always implied even if it is not specified.
  • The assignment value follows the same rules as for an Assignment Statement.
  • In addition to the standard types, you may specify EXCEPTION if declaring an exception variable.

3.9.6. Assignment Statement
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An assignment statement assigns a value to a variable by evaluating an expression.
Usage: 
<variable reference> = <expression>;
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Example Syntax

  • myString = 'Thank you';
VARIABLES.x = (SELECT Column1 FROM MySchema.MyTable);
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Special Variables

  • The VARIABLES.ROWCOUNT integer variable will contain the numbers of rows affected by the last INSERT/UPDATE/DELETE command statement executed. Inserts that are processed by dynamic SQL with an INTO clause will also update the ROWCOUNT.

    Example 3.15. Sample Usage

    ...
UPDATE FOO SET X = 1 WHERE Y = 2;
DECLARE INTEGER UPDATED = VARIABLES.ROWCOUNT;
...
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3.9.7. Compound Statement
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A compound statement (or block) logically groups a series of statements. Temporary tables and variables created in a compound statement are local only to that block and are destroyed when exiting the block.
Usage: 
[label :] BEGIN [[NOT] ATOMIC]
    statement*
[EXCEPTION ex
    statement*
]
END
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Note

Where a block is expected by an IF, LOOP, WHILE, etc., a single statement is also accepted by the parser. Even though the block BEGIN/END are not expected, the statement will execute as if wrapped in a BEGIN/END pair.

Syntax Rules

  • If NOT ATOMIC or no ATOMIC clause is specified, the block will be executed non-atomically.
  • If the ATOMIC clause is specified, the block must execute atomically. If a transaction is already associated with the thread, no additional action will be taken - savepoints and/or sub-transactions are not currently used. Otherwise a transaction will be associated with the execution of the block.
  • The label must not be the same as any other label used in statements containing this one.

3.9.8. Exception Handling
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If the EXCEPTION clause is used within a compound statement, any processing exception emitted from statements will be caught with the flow of execution transferring to EXCEPTION statements. Any block level transaction started by this block will commit if the exception handler successfully completes. If another exception or the original exception is emitted from the exception handler the transaction will rollback. Any temporary tables or variables specific to the BLOCK will not be available to the exception handler statements.

Note

Only processing exceptions, which are typically caused by errors originating at the sources or with function execution, are caught. A low-level internal error or Java RuntimeException will not be caught.
To aid in the processing of a caught exception the EXCEPTION clause specifies a group name that exposes the significant fields of the exception. The exception group will contain:
Expand
Variable
Type
Description
STATE
string
The SQL State
ERRORCODE
integer
The error or vendor code. In the case of an internal exception, this will be the integer suffix of the TEIIDxxxx code
TEIIDCODE
string
The full event code. Typically TEIIDxxxx.
EXCEPTION
object
The exception being caught, will be an instance of TeiidSQLException
CHAIN
object
The chained exception or cause of the current exception

Note

JBoss Data Virtualization does not yet fully comply with the ANSI SQL specification on SQL State usage. For errors without an underlying SQLException cause, it is best to use the event code.
The exception group name may not be the same as any higher level exception group or loop cursor name.

Example 3.16. Example Exception Group Handling

BEGIN
    DECLARE EXCEPTION e = SQLEXCEPTION 'this is bad' SQLSTATE 'xxxxx';
    RAISE variables.e;
EXCEPTION e
    IF (e.state = 'xxxxx')
        //in this trivial example, we'll always hit this branch and log the exception
        RAISE SQLWARNING e.exception;
    ELSE
        RAISE e.exception;
END
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3.9.9. If Statement
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An IF statement evaluates a condition and executes one of two statements depending on the result. You can nest IF statements to create complex branching logic. A dependent ELSE statement will execute its statement only if the IF statement evaluates to false.
Usage: 
IF (criteria)
  block
[ELSE
  block]
END
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Example 3.17. Example If Statement

IF ( var1 = 'North America')
BEGIN
  ...statement...
END ELSE
BEGIN
  ...statement...
END
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Note

NULL values should be considered in the criteria of an IF statement. IS NULL criteria can be used to detect the presence of a NULL value.

3.9.10. Loop Statement
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A LOOP statement is an iterative control construct that is used to cursor through a result set.
Usage: 
[label :] LOOP ON <select statement> AS <cursorname>
  block
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Syntax Rules

  • The label must not be the same as any other label used in statements containing this one.

3.9.11. While Statement
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A WHILE statement is an iterative control construct that is used to execute a block repeatedly whenever a specified condition is met.
Usage: 
[label :] WHILE <criteria>
  block
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Syntax Rules

  • The label must not be the same as any other label used in statements containing this one.

3.9.12. Continue Statement
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A CONTINUE statement is used inside a LOOP or WHILE construct to continue with the next loop by skipping over the rest of the statements in the loop. It must be used inside a LOOP or WHILE statement.
Usage: 
CONTINUE [label];
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Syntax Rules

  • If the label is specified, it must exist on a containing LOOP or WHILE statement.
  • If no label is specified, the statement will affect the closest containing LOOP or WHILE statement.

3.9.13. Break Statement
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A BREAK statement is used inside a LOOP or WHILE construct to break from the loop. It must be used inside a LOOP or WHILE statement.
Usage: 
BREAK [label];
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Syntax Rules

  • If the label is specified, it must exist on a containing LOOP or WHILE statement.
  • If no label is specified, the statement will affect the closest containing LOOP or WHILE statement.

3.9.14. Leave Statement
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A LEAVE statement is used inside a compound, LOOP, or WHILE construct to leave to the specified label.
Usage: 
LEAVE label;
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Syntax Rules

  • The label must exist on a containing compound statement, LOOP, or WHILE statement.

3.9.15. Return Statement
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A Return statement gracefully exits the procedure and optionally returns a value.
Usage: 
RETURN [expression];
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Syntax Rules

  • If an expression is specified, the procedure must have a return parameter and the value must be implicitly convertible to the expected type.
  • Even if the procedure has a return value, it is not required to specify a return value in a RETURN statement.

3.9.16. Error Statement
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An ERROR statement declares that the procedure has entered an error state and should abort. This statement will also roll back the current transaction, if one exists. Any valid expression can be specified after the ERROR keyword.
Usage: 
ERROR message;
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Example 3.18. Example Error Statement

ERROR 'Invalid input value: ' || nvl(Acct.GetBalance.AcctID, 'null');
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An ERROR statement is equivalent to: 
RAISE SQLEXCEPTION message;
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3.9.17. Raise Statement
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A RAISE statement is used to raise an exception or warning. When raising an exception, this statement will also roll back the current transaction, if one exists.
Usage: 
RAISE [SQLWARNING] exception;
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Where exception may be a variable reference to an exception or an exception expression.

Syntax Rules

  • If SQLWARNING is specified, the exception will be sent to the client as a warning and the procedure will continue to execute.
  • A null warning will be ignored. A null non-warning exception will still cause an exception to be raised.

Example 3.19. Example Raise Statement

RAISE SQLWARNING SQLEXCEPTION 'invalid' SQLSTATE '05000';
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3.9.18. Exception Expression
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An exception expression creates an exception that can be raised or used as a warning.
Usage: 
SQLEXCEPTION message [SQLSTATE state [, code]] CHAIN exception
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Syntax Rules

  • Any of the values may be null;
  • message and state are string expressions specifying the exception message and SQL state respectively. JBoss Data Virtualization does not yet fully comply with the ANSI SQL specification on SQL state usage, but you are allowed to set any SQL state you choose.
  • code is an integer expression specifying the vendor code
  • exception must be a variable reference to an exception or an exception expression and will be chained to the resulting exception as its parent.
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