Oracle應用遷移到AnalyticDB for PostgreSQL指導
AnalyticDB for PostgreSQL(簡稱:ADB for PG)對Oracle語法有著較好的相容,本文介紹如何將Oracle應用遷移到AnalyticDB for PostgreSQL。
1 PL/SQL
PL/SQL(Procedural Language/SQL)是一種過程化的SQL語言,是Oracle對SQL語句的拓展,使得SQL的使用可以具有一般程式語言的特點,因此,可以用來實現複雜的業務邏輯。PL/SQL對應了ADB for PG中的PL/PGSQL
1.1Package
ADB for PG的plpgsql不支援package,需要把package 轉換成 schema,並package裡面的所有procedure和 function轉換成ADB for PG的function。
例如:
create or replace package pkg is
…
end;
可以轉換成:
create schema pkg;
-
Package定義的變數
procedure/function的區域性變數保持不變,全域性變數在ADB for PG中可以使用臨時表進行儲存。詳見1.4.5節。
-
Package初始化塊
如果可以刪掉,就刪掉,刪不掉的話,可以使用function封裝,在需要的時候主動呼叫該function。
-
Package 內定義的procedure/function
Package 內定義的procedure和function 轉成adb for pg的function,並把function 定義到package對應的schema內。 例如,有一個Package名為pkg中有如下函式:
FUNCTION test_func (args int) RETURN int is var number := 10; BEGIN … … END;
轉換成如下ADB for PG的function:
CREATE OR REPLACE FUNCTION pkg. test_func(args int) RETURNS int AS $$ … … $$ LANGUAGE plpgsql;
1.2 Procedure/function
對於oracle的procedure和function,不論是package的還是全域性的,都轉換成adb for pg 的function。
例如:
CREATE OR REPLACE FUNCTION test_func (v_name varchar2, v_version varchar2)
RETURN varchar2 IS
ret varchar(32);
BEGIN
IF v_version IS NULL THEN
ret := v_name;
ELSE
ret := v_name || '/' || v_version;
END IF;
RETURN ret;
END;
轉化成:
CREATE OR REPLACE FUNCTION test_func (v_name varchar, v_version varchar)
RETURNS varchar AS
$$
DECLARE
ret varchar(32);
BEGIN
IF v_version IS NULL THEN
ret := v_name;
ELSE
ret := v_name || '/' || v_version;
END IF;
RETURN ret;
END;
$$
LANGUAGE plpgsql;
Procedure/function轉換的關鍵點:
- RETURN 關鍵字轉成RETURNS
- 函式體使用$\$ ... $\$封裝起來
- 函式語言宣告
- Subprocedure需要轉換成ADB for PG的function
1.3 PL statement
1.3.1 For語句
帶有REVERSE的整數FOR迴圈的工作方式不同:PL/SQL中是從第二個數向第一個數倒數,而PL/pgSQL是從第一個數向第二個數倒數,因此在移植時需要交換迴圈邊界。
示例:
FOR i IN REVERSE 1..3 LOOP
DBMS_OUTPUT.PUT_LINE (TO_CHAR(i));
END LOOP;
轉換成:
FOR i IN REVERSE 3..1 LOOP
RAISE ‘%’ ,i;
END LOOP;
1.3.2 PRAGMA語句
ADB for PG 無PRAGMA語句,刪除。
1.3.3 事務處理
ADB for PG 的function 內部無法使用事務控制語句,如begin,commit,rollback等。
修改方法:
- 刪除函式體內的事務控制語句,把事務控制放在函式體外;
- 把函式按照commit/rollback 拆分成多個。
1.3.4 EXECUTE語句
ADB for PG支援類似oracle的動態sql語句,不同之處如下:
- 不支援using 語法,解決方法是把引數拼接到sql串中;
- 資料庫識別符號使用quote_ident包裹,數值使用quote_literal包裹。
示例:
EXECUTE 'UPDATE employees_temp SET commission_pct = :x' USING a_null;
轉換成:
EXECUTE 'UPDATE employees_temp SET commission_pct = ' || quote_literal(a_null);
1.3.5 Pipe row
Pipe row函式,使用adb for pg的table function來替換。
示例:
TYPE pair IS RECORD(a int, b int);
TYPE numset_t IS TABLE OF pair;
FUNCTION f1(x int) RETURN numset_t PIPELINED IS
DECLARE
v_p pair;
BEGIN
FOR i IN 1..x LOOP
v_p.a := i;
v_p.b := i+10;
PIPE ROW(v_p);
END LOOP;
RETURN;
END;
select * from f1(10);
轉換成:
create type pair as (a int, b int);
create or replace function f1(x int) returns setof pair as
$$
declare
rec pair;
begin
for i in 1..x loop
rec := row(i, i+10);
return next rec;
end loop;
return ;
end
$$
language 'plpgsql';
select * from f1(10);
說明:
- 自定義型別pair轉換成adb for pg的複合型別pair
- Table of型別不需要定義,使用adb for pg的setof 替換
-
Pipe row 語句轉換成下面兩個語句:
rec := row(i); return next rec;
-
上面的oracle function還可以轉換成如下:
create or replace function f1(x int) returns setof record as $$ declare rec record; begin for i in 1..x loop rec := row(i, i+10); return next rec; end loop; return ; end $$ language 'plpgsql';
與第一種改法的不同支援是,不需要提前定義資料型別numset_t.正因為這一點所以在查詢的時候需要指定返回的型別,如下:select * from f1(10) as (a int, b int);
1.3.6 異常處理
- 使用raise丟擲異常
- Catch異常後,不能rollback事務,只能在udf外做rollback
- ADB for PG支援的error,可以參考: https://www.postgresql.org/docs/8.3/errcodes-appendix.html
1.3.7 function中同時有Return和OUT引數
在adb pg中,不允許fucntion同時有return和out引數,因此,可以把需要返回的引數改寫成out型別引數。
示例:
CREATE OR REPLACE FUNCTION test_func(id int, name varchar(10), out_id out int) returns varchar(10)
AS $body$
BEGIN
out_id := id + 1;
return name;
end
$body$
LANGUAGE PLPGSQL;
改寫成:
CREATE OR REPLACE FUNCTION test_func(id int, name varchar(10), out_id out int, out_name out varchar(10))
AS $body$
BEGIN
out_id := id + 1;
out_name := name;
end
$body$
LANGUAGE PLPGSQL;
然後select * from test_func(1,’1’) into rec;從rec中取對應欄位的返回值即可。
1.4 PL資料型別
1.4.1 Record
使用ADB for PG的複合資料型別替換
示例:
TYPE rec IS RECORD (a int, b int);
改寫成:
CREATE TYPE rec AS (a int, b int);
1.4.2 Nest table
- Nest table 作為pl 變數,可以使用ADB for PG的array型別替換。
示例:
DECLARE
TYPE Roster IS TABLE OF VARCHAR2(15);
names Roster :=
Roster('D Caruso', 'J Hamil', 'D Piro', 'R Singh');
BEGIN
FOR i IN names.FIRST .. names.LAST
LOOP
IF names(i) = 'J Hamil' THEN
DBMS_OUTPUT.PUT_LINE(names(i));
END IF;
END LOOP;
END;
改寫成:
create or replace function f1() returns void as
$$
declare
names varchar(15)[] := '{"D Caruso", "J Hamil", "D Piro", "R Singh"}';
len int := array_length(names, 1);
begin
for i in 1..len loop
if names[i] = 'J Hamil' then
raise notice '%', names[i];
end if;
end loop;
return ;
end
$$
language 'plpgsql';
select f();
- 作為function返回值,則可以使用table function替換,參考1.3.5節。
1.4.3 Associative Array
無替換型別。
1.4.4 Variable-Size Arrays
與nest table 一樣,使用array型別替換。
1.4.5 Global variables
目前ADB for PG不支援global variables,一種方法是把一個package中的所有global variables存入一張臨時表(temporary table)中, 然後定義修改、獲取global variables的函式。
示例:
create temporary table global_variables (
id int,
g_count int,
g_set_id varchar(50),
g_err_code varchar(100)
);
insert into global_variables values(0, 1, null,null);
CREATE OR REPLACE FUNCTION get_variable() returns setof global_variables AS
$$
DECLARE
rec global_variables%rowtype;
BEGIN
execute 'select * from global_variables' into rec;
return next rec;
END;
$$
LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION set_variable(in param varchar(50), in value anyelement) returns void AS
$$
BEGIN
execute 'update global_variables set ' || quote_ident(param) || ' = ' || quote_literal(value);
END;
$$
LANGUAGE plpgsql;
其中,臨時表global_variables中,欄位id為這個表的分佈列,因為ADB for PG中不允許對於分佈列的修改,需要多加一個這樣的欄位。
tmp_rec record;
修改一個全域性變數時,使用:select * from set_variable(‘g_error_code’, ‘error’::varchar) into tmp_rec;
獲取一個全域性變數時,使用:select * from get_variable() into tmp_rec; error_code := tmp_rec.g_error_code;
1.5 SQL
1.5.1 Connect by
Oracle 層次查詢,adb for pg沒有等價替換的sql語句。轉換思路是使用迴圈按層次遍歷。
示例:
create table employee(
emp_id numeric(18),
lead_id numeric(18),
emp_name varchar(200),
salary numeric(10,2),
dept_no varchar(8)
);
insert into employee values('1',0,'king','1000000.00','001');
insert into employee values('2',1,'jack','50500.00','002');
insert into employee values('3',1,'arise','60000.00','003');
insert into employee values('4',2,'scott','30000.00','002');
insert into employee values('5',2,'tiger','25000.00','002');
insert into employee values('6',3,'wudde','23000.00','003');
insert into employee values('7',3,'joker','21000.00','003');
insert into employee values('3',7,'joker','21000.00','003');
select emp_id,lead_id,emp_name,prior emp_name as lead_name,salary
from employee
start with lead_id=0
connect by prior emp_id = lead_id
轉換成:
create or replace function f1(tablename text, lead_id int, nocycle boolean) returns setof employee as
$$
declare
idx int := 0;
res_tbl varchar(265) := 'result_table';
prev_tbl varchar(265) := 'tmp_prev';
curr_tbl varchar(256) := 'tmp_curr';
current_result_sql varchar(4000);
tbl_count int;
rec record;
begin
execute 'truncate ' || prev_tbl;
execute 'truncate ' || curr_tbl;
execute 'truncate ' || res_tbl;
loop
-- 查詢當前層次結果,並插入到tmp_curr表
current_result_sql := 'insert into ' || curr_tbl || ' select t1.* from ' || tablename || ' t1';
if idx > 0 then
current_result_sql := current_result_sql || ', ' || prev_tbl || ' t2 where t1.lead_id = t2.emp_id';
else
current_result_sql := current_result_sql || ' where t1.lead_id = ' || lead_id;
end if;
execute current_result_sql;
-- 如果有環,刪除已經遍歷過的資料
if nocycle is false then
execute 'delete from ' || curr_tbl || ' where (lead_id, emp_id) in (select lead_id, emp_id from ' || res_tbl || ') ';
end if;
-- 如果沒有資料,則退出
execute 'select count(*) from ' || curr_tbl into tbl_count;
exit when tbl_count = 0;
-- 把tmp_curr資料儲存到result表
execute 'insert into ' || res_tbl || ' select * from ' || curr_tbl;
execute 'truncate ' || prev_tbl;
execute 'insert into ' || prev_tbl || ' select * from ' || curr_tbl;
execute 'truncate ' || curr_tbl;
idx := idx + 1;
end loop;
-- 返回結果
current_result_sql := 'select * from ' || res_tbl;
for rec in execute current_result_sql loop
return next rec;
end loop;
return;
end
$$
language plpgsql;
1.5.2 Rownum
- 限定查詢結果集大小,可以使用limit替換
示例:
select * from t where rownum < 10;
轉換成:
select * from t limit 10;
- 使用row_number() over()生成rownum
示例:
select rownum, * from t;
轉換成:
select row_number() over() as rownum, * from t;
1.5.3 Dual表
- 去掉dual
示例:
select sysdate from dual;
轉換成:
select current_timestamp;
- 建立一個叫dual的表。
1.5.4 Select中的udf
ADB for PG支援在select中呼叫udf,但是udf中不能有sql語句,否則會收到如下的錯誤資訊:
ERROR: function cannot execute on segment because it accesses relation "public.t2" (functions.c:155) (seg1 slice1 127.0.0.1:25433 pid=52153) (cdbdisp.c:1326)
DETAIL:
SQL statement "select b from t2 where a = $1 "
轉換方法是把select中的udf轉換成sql表示式或者子查詢等
示例:
create or replace FUNCTION f1(arg int) RETURN int IS
v int;
BEGIN
select b into v from t2 where a = arg;
return v;
END;
select a, f1(b) from t1;
轉換成:
select t1.a, t2.b from t1, t2 where t1.b = t2.a;
1.5.5 (+)多表外連結
ADB for PG 不支援(+)這樣的語法形式,需要轉換成標準的outer join語法。
示例:
oracle
select * from a,b where a.id=b.id(+)
轉換成:
select * from a left join b on a.id=b.id
如果在(+)中有三表的join,需要先用wte做兩表的join,再用+號那個表跟wte表做outer join。
示例:
Select * from test1 t1, test2 t2, test3 t3 where t1.col1(+) between NVL(t2.col1, t3.col1) and NVL(t3.col1, t2.col1);
轉換成:
with cte as (select t2.col1 as low, t2.col2, t3.col1 as high, t3.col2 as c2 from t2, t3)
select * from t1 right outer join cte on t1.col1 between coalesce(cte.low, cte.high) and coalesce(cte.high,cte.low);
1.5.6 Merge into
對於merge into語法的轉換,在ADB for PG中先使用update進行更新,然後使用GET DIAGNOSTICS rowcount := ROW_COUNT;語句獲取update更新的行數,如果update更新的行數為0,那麼再使用insert語句進行插入。
MERGE INTO test1 t1
USING (SELECT t2.col1 col1, t3.col2 col2,
FROM test2 t2, test3 t3) S
ON S.col1 = 1 and S.col2 = 2
WHEN MATCHED THEN
UPDATE
SET test1.col1 = S.col1+1,
test1.col2 = S.col2+2
WHEN NOT MATCHED THEN
INSERT (col1, col2)
VALUES
(S.col1+1, S.col2+2);
轉換成:
Update test1 t1 SET t1.col1 = test2.col1+1, test3.col2 = S.col2+2 where test2.col1 = 1 and test2.col2 = 2;
GET DIAGNOSTICS rowcount := ROW_COUNT;
if rowcount = 0 then
insert into test1 values(test2.col1+1, test3.col2+2);
2 系統函式轉換對照表
oracle | ADB for PG |
---|---|
sysdate | current timestamp |
trunc | trunc/ date trunc |
dbms_output.put_line | raise 語句 |
decode | 轉成case when/直接使用decode |
NVL | coalesce |
3 資料型別轉換對照表
oracle | ADB for PG |
---|---|
sysdate | current timestamp |
trunc | trunc/ date trunc |
dbms_output.put_line | raise 語句 |
decode | 轉成case when/直接使用decode |
NVL | coalesce |
oracle | ADB for PG |
---|---|
VARCHAR2 | varchar or text |
DATE | timestamp |
LONG | text |
LONG RAW | bytea |
CLOB | text |
NCLOB | text |
BLOB | bytea |
RAW | bytea |
ROWID | oid |
FLOAT | double precision |
DEC | decimal |
DECIMAL | decimal |
DOUBLE PRECISION | double precision |
INT | int |
INTERGE | integer |
REAL | real |
SMALLINT | smallint |
NUMBER | numeric |
BINARY_FLOAT | double precision |
BINARY_DOUBLE | double precision |
TIMESTAMP | timestamp |
XMLTYPE | xml |
BINARY_INTEGER | integer |
PLS_INTEGER | integer |
TIMESTAMP WITH TIME ZONE | timestamp with time zone |
TIMESTAMP WITH LOCAL TIME ZONE | timestamp with time zone |
原文連結
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