Oracle中的動態sql

Question

如何根據if else語句在oracle中創建動態sql。

sql:= 'select n from where a = p_a'; 
if p_b is not null then 
sql:= 'select n from where a = p_a and b = p_b';  

Answer 1

爲什麼只要執行以下操作即可獲得動態SQL？

select n 
from xx 
where a = p_a and (b = p_b or p_b is null); 

Answer 2

例子：

CREATE TYPE t_emp AS OBJECT (id NUMBER, name VARCHAR2(20)) 
/
CREATE TYPE t_emplist AS TABLE OF t_emp 
/

CREATE TABLE dept_new (id NUMBER, emps t_emplist) 
    NESTED TABLE emps STORE AS emp_table; 

INSERT INTO dept_new VALUES (
    10, 
    t_emplist(
     t_emp(1, 'SCOTT'), 
     t_emp(2, 'BRUCE'))); 

DECLARE 
    deptid NUMBER; 
    ename VARCHAR2(20); 
BEGIN 
    EXECUTE IMMEDIATE 'SELECT d.id, e.name 
     FROM dept_new d, TABLE(d.emps) e -- not allowed in static SQL 
              -- in PL/SQL 
     WHERE e.id = 1' 
     INTO deptid, ename; 
END; 
/

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