Oracle和PostgreSQL都提供了內建的程式語言（PL/SQL vs PL/pgSQL），在輸入輸出引數的宣告上有較大的不同，如輸入引數中存在inout/out引數，Oracle的函式可以有返回值，但PG不允許有返回值，只能透過引數返回。

**Oracle**
建立函式
```
TEST-orcl@DESKTOP-V430TU3>CREATE or replace FUNCTION sf_testparameter(p1 varchar2,p2 int,p3 varchar2,p4  in out int)
  2  RETURN varchar2
  3  is
  4  begin
  5    p4 := 1;
  6    return 'test';
  7  end;
  8  /

Function created.

```

執行
```
TEST-orcl@DESKTOP-V430TU3>select sf_testparameter(null,null,null,:p4) from dual;
select sf_testparameter(null,null,null,:p4) from dual
       *
ERROR at line 1:
ORA-06572: Function SF_TESTPARAMETER has out arguments
```
不能在SQL中執行，但可以在PL/SQL中執行
```
TEST-orcl@DESKTOP-V430TU3>set serveroutput on
TEST-orcl@DESKTOP-V430TU3>declare
  2    p4 number;
  3    ret varchar2(100);
  4  begin
  5    ret := sf_testparameter(null,null,null,p4);
  6    dbms_output.put_line('p4 = '||p4||',ret='||ret);
  7  end;
  8  /
p4 = 1,ret=test
```

**PostgreSQL**
建立函式，引數中存在inout型別的引數，返回值必須與該引數型別一樣，而且return不能返回實際值。
```
[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int)
pg12@testdb-#   RETURNS text 
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return 'test';
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
ERROR:  function result type must be integer because of OUT parameters
[local:/data/run/pg12]:5120 pg12@testdb=# 
[local:/data/run/pg12]:5120 pg12@testdb=# drop function sf_testparameter;
ERROR:  could not find a function named "sf_testparameter"
[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int)
pg12@testdb-#   RETURNS int 
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return 1;
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
ERROR:  RETURN cannot have a parameter in function with OUT parameters
LINE 5:   return 1;
                 ^
[local:/data/run/pg12]:5120 pg12@testdb=#

[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int)
pg12@testdb-#   RETURNS int 
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return;
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
CREATE FUNCTION
[local:/data/run/pg12]:5120 pg12@testdb=# select sf_testparameter(null,null,null,null);
 sf_testparameter 
------------------
                 
(1 row)

[local:/data/run/pg12]:5120 pg12@testdb=#

```
如引數中有多個out引數，則要求返回record型別
```
[local:/data/run/pg12]:5120 pg12@testdb=# drop function sf_testparameter;
ION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int,out p5 text)
  RETURNS record
  AS $$
begin
  return;
end;
$$ LANGUAGE 'plpgsql';

\df sf_testparameter

select sf_testparameter(null,null,null,null,null);
select sf_testparameter(null,null,null,null);
DROP FUNCTION
[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int,out p5 text)
pg12@testdb-#   RETURNS text 
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return 'test';
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
ERROR:  function result type must be record because of OUT parameters
[local:/data/run/pg12]:5120 pg12@testdb=# 
[local:/data/run/pg12]:5120 pg12@testdb=# drop function sf_testparameter;
ERROR:  could not find a function named "sf_testparameter"
[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int,out p5 text)
pg12@testdb-#   RETURNS record
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return;
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
CREATE FUNCTION
[local:/data/run/pg12]:5120 pg12@testdb=# 
[local:/data/run/pg12]:5120 pg12@testdb=# \df sf_testparameter
List of functions
-[ RECORD 1 ]-------+------------------------------------------------------------
Schema              | public
Name                | sf_testparameter
Result data type    | record
Argument data types | p1 text, p2 integer, p3 text, INOUT p4 integer, OUT p5 text
Type                | func

[local:/data/run/pg12]:5120 pg12@testdb=# 
[local:/data/run/pg12]:5120 pg12@testdb=# select sf_testparameter(null,null,null,null,null);
ERROR:  function sf_testparameter(unknown, unknown, unknown, unknown, unknown) does not exist
LINE 1: select sf_testparameter(null,null,null,null,null);
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
[local:/data/run/pg12]:5120 pg12@testdb=# select sf_testparameter(null,null,null,null);
 sf_testparameter 
------------------
 (,)
(1 row)

[local:/data/run/pg12]:5120 pg12@testdb=#

```
不管有多少個out引數，都歸為return引數，在呼叫時不需要作為引數輸入，難怪PG要求返回record型別。
```

[local:/data/run/pg12]:5120 pg12@testdb=# drop function sf_testparameter;
DROP FUNCTION
[local:/data/run/pg12]:5120 pg12@testdb=# CREATE or replace FUNCTION sf_testparameter(p1 text,p2 int,p3 text,inout p4 int,out p5 text,out p6 text)
pg12@testdb-#   RETURNS record
pg12@testdb-#   AS $$
pg12@testdb$# begin
pg12@testdb$#   return;
pg12@testdb$# end;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
CREATE FUNCTION
[local:/data/run/pg12]:5120 pg12@testdb=# select sf_testparameter(null,null,null,null);
 sf_testparameter 
------------------
 (,,)
(1 row)

[local:/data/run/pg12]:5120 pg12@testdb=# 
[local:/data/run/pg12]:5120 pg12@testdb=#

```

**參考資料**
N/A

Oracle vs PostgreSQL Develop（23） - PL(pg)sql(引數宣告)

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