《Oracle PL/SQL開發指南》學習筆記31——原始碼除錯——函式和過程（第二部分，函式）
1. 命名塊函式原型
[{EDITIONALBE | NONEDITIONALBE}] FUNCTION function_name ( parameter [IN][OUT] [NOCOPY] sql_datatype | plsql_datatype [, parameter [IN][OUT] [NOCOPY] sql_datatype | plsql_datatype [, ... ]]) RETURN [ sql_data_type | plsql_data_type ] [ AUTHID [ DEFINER | CURRENT_USER ]] [ DETERMINISTIC | PARALLEL_ENABLE ] [ PIPELINED ] [ACCESSIBLE BY ( [{FUNCTION | PROCEDURE | PACKAGE | TYPE}] [schema.]unit_name) [,[{FUNCTION | PROCEDURE | PACKAGE | TYPE}] [schema.]unit_name)] [,... ]]]) [ RESULT_CACHE [ RELIES ON table_name [, table_name [, ...]]]] IS declaration_statements BEGIN execution_statements RETURN variable; [EXCEPTION] exception_handling_statements END [function_name]; /
SQL*PLUS中用實參進行函式呼叫的原型：
CALL function_name(parameter [, parameter [, ...]])
INTO target_variable_name;如果沒有強制引數，原型會有所不同：
CALL function_name INTO target_variable_name;PL/SQL塊中帶有強制引數的賦值為：
target_variable_name :=
function_name(parameter [, parameter [, ...]]);沒有強制引數時括號可省略：
target_variable_name := function_name;
也可以將函式的返回值作為另一函式的實參返回（實際工作中有時需要多層巢狀函式）：
external_function_name(function_name( parameter
[, parameter [, ...]]));2.Oracle Pragma限制選項
| Option | Description |
| RNDS | The RNDS option guarantees a function reads no data state. This means you cannot include a SQL query of any type in the function. It also cannot call any other named block that includes a SQL query. A PLS-00452 error is raised during compilation if you have a query inside the function’s program scope that violates the PRAGMA restriction. |
| WNDS | The WNDS option guarantees a function writes no data state. This means you cannot include SQL statements that insert, update, or delete data. It also cannot call any other named block that includes a SQL query. A PLS-00452 error is raised during compilation if you have a DML statement inside the function’s program scope that violates the PRAGMA restriction. |
| RNPS | The RNPS option guarantees a function reads no package state, which means that it does not read any package variables. This means you cannot access a package variable in the function. It also cannot call any other named block that reads package variables. A PLS-00452 error is raised during compilation if you have a query inside the function’s program scope that violates the PRAGMA restriction. |
| WNPS | The WNPS options guarantees a function writes no package state, which means that it does not write any values to package variables. This means you cannot change package variables or call another named block that changes them. A PLS-00452 error is raised during compilation if you have a statement inside the function’s program scope that violates the PRAGMA restriction. |
| TRUST | The TRUST option instructs the function not to check whether called programs enforce other RESTRICT_REFERENCES options. The benefit of this option is that you can slowly migrate code to the new standard. The risks include changing the behavior or performance of SQL statements. For reference, the other options guard conditions necessary to support function-based indexes and parallel query operations. |
3. DETERMINISTIC子句（第一次接觸）
DETERMINISTIC子句可用於保證函式對於任意次相同的輸入產生相同的輸出結果（確定性結果，deterministic result），而不諸如快取等因素的影響。
示例：
SQL> CREATE OR REPLACE FUNCTION pv
2 ( future_value NUMBER
3 , periods NUMBER
4 , interest NUMBER )
5 RETURN NUMBER DETERMINISTIC IS
6 BEGIN
7 RETURN future_value / ((1 + interest/100)**periods);
8 END pv;
9 /
函式已建立。
SQL> VARIABLE result NUMBER
SQL> CALL pv(3000000,20,6) INTO :result;
呼叫完成。
SQL> COLUMN money_today FORMAT 999,999,999.00
SQL> COLUMN money_today FORMAT $999,999,999.00
SQL> SELECT :result AS money_today
2 FROM dual;
MONEY_TODAY
----------------
$935,414.18順便了解一下物化檢視吧：
Materialized Views
Unlike a standard view in a relational database, a materialized view is a cached result set. As a cached result set, it is stored as a concrete table. Materialized views are more responsive to queries because they don’t demand resources to dynamically build the view each time. The trade-off is that materialized views are often slightly out of date because underlying data may change between when the view is cached versus it is accessed. You can use function-based indexes in materialized views provided they use deterministic functions. Deterministic functions always produce the same result value when called with any set of actual parameters. They also guarantee that they don’t modify package variables or data in the database. Consider using materialized views when the underlying table data changes infrequently and query speed is important. Materialized views are possible solutions when developing data warehouse fact tables. You use deterministic functions inside materialized views and function-based indexes. Both materialized views and function-based indexes must be rebuilt when you change the internal working of deterministic functions.