Oracle vs PostgreSQL Develop（17） - ARRAY

postgresql可用ARRAY来替代oracle中的collection type,包括associative array/Varrays (Variable-Size Arrays)/Nested Tables

Oracle
简单举个例子:

drop table if exists employee;
create table employee(id int,name varchar(30),department varchar(30),salary float);
insert into employee(id,name,department,salary) select rownum,substrb(object_name,1,30),substrb(object_name,1,30),1000 from dba_objects;
DECLARE
   TYPE EmpTabTyp IS TABLE OF employee%ROWTYPE
      INDEX BY PLS_INTEGER;
   emp_tab EmpTabTyp;
   i int := 0;
BEGIN
   
   for c1 in (select * from employee) loop
     emp_tab(i).id := c1.id;
     emp_tab(i).name := c1.name;
     emp_tab(i).department := c1.department;
     emp_tab(i).salary := c1.salary;
     i := i+1;
   end loop;
   -- SELECT * INTO emp_tab(100) FROM employee WHERE id = 100;
END;
/

更简单的做法是使用bulk collection

DECLARE
   TYPE EmpTabTyp IS TABLE OF employee%ROWTYPE
      INDEX BY PLS_INTEGER;
   emp_tab EmpTabTyp;
   i int := 0;
BEGIN
   
   select id,name,department,salary bulk collect into emp_tab from employee;
END;
/

PostgreSQL
使用ARRAY

drop type record_of_employee;
CREATE TYPE record_of_employee AS (id int,name varchar(30),department varchar(30),salary float);
do
$$
declare
  employees record_of_employee[];
begin
  select array_agg(employee) into employees from employee limit 1;
  raise notice 'id is %',employees[1].id;
  raise notice 'name is %',employees[1].name;
end
$$;

对于Associative array indexed by string,PG的数组则替代不了.

DECLARE
  -- Associative array indexed by string:
  TYPE population IS TABLE OF NUMBER  -- Associative array type
    INDEX BY VARCHAR2(64);            --  indexed by string
...

参考资料
PL/sql Collections and Records
Oracle PL/SQL Collections: Varrays, Nested & Index by Tables
Collections in Oracle PL/SQL
Working with Collections
Take a Dip into PostgreSQL Arrays