SELECT * FROM MySchema.MyTable WHERE ColA > 100; INSERT INTO MySchema.MyTable (ColA,ColB) VALUES (50, 'hi');
Teiid 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.
A command statement executes a SQL Commands , such as SELECT, INSERT, UPDATE, DELETE, or EXECUTE, against one or more data sources.
SELECT * FROM MySchema.MyTable WHERE ColA > 100; INSERT INTO MySchema.MyTable (ColA,ColB) VALUES (50, 'hi');
EXECUTE command statements 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 datatype of parameter will be implicitly convertable to the datatype of the variable.
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>]
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.
... /* 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 ...
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.
... 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; ...
Known Limitations and Work-Arounds
The use of dynamic SQL command results in an assignment statement requires the use of a temp table.
EXECUTE IMMEDIATE <expression> AS x string INTO #temp; DECLARE string VARIABLES.RESULT = (SELECT x FROM #temp);
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.
... criteria = ‘(‘ || criteria || ‘ and (Customer.Accounts.Birthdate = DVARS.BirthDay))’;
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.
... criteria = ‘(‘ || nvl(criteria, ‘(1 = 1)’) || ‘ and (Customer.Accounts.Birthdate = DVARS.BirthDay))’;
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.
/* This name does not need to match the expected update command symbol "count". */ EXECUTE IMMEDIATE <expression> AS x integer INTO #temp;
Unless used in other parts of the procedure, tables in the dynamic command will not be seen as sources in the Designer.
When using the "AS" clause only the type information will be available to the Designer. ResultSet columns generated from the "AS" clause then will have a default set of properties for length, precision, etc.
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>];
declare integer x; declare string VARIABLES.myvar = 'value';
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.
An assignment statement assigns a value to a variable by either evaluating an expression.
Usage:
<variable reference> = <expression>;
Example Syntax
myString = 'Thank you'; VARIABLES.x = (SELECT Column1 FROM MySchema.MyTable);
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.
... UPDATE FOO SET X = 1 WHERE Y = 2; DECLARE INTEGER UPDATED = VARIABLES.ROWCOUNT; ...
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 are destroyed when exiting the block.
Usage:
[label :] BEGIN \[[NOT] ATOMIC]
statement*
END
When a block is expected by a 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 ATOMIC 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.
An IF statement evaluates a condition and executes either 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
IF ( var1 = 'North America') BEGIN ...statement... END ELSE BEGIN ...statement... END
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.
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
Syntax Rules
The label must not be the same as any other label used in statements containing this one.
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
Syntax Rules
The label must not be the same as any other label used in statements containing this one.
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];
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.
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];
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.
A LEAVE statement is used inside a compound, LOOP, or WHILE construct to leave to the specified level.
Usage:
LEAVE label;
Syntax Rules
The label must exist on a containing compound statement, LOOP, or WHILE statement.
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;
ERROR 'Invalid input value: ' || nvl(Acct.GetBalance.AcctID, 'null');