oracle wm concat函式 用於列轉行 逗號分隔
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wm_concat函式
首先讓我們來看看這個神奇的函式wm_concat(列名),該函式可以把列值以","號分隔起來,並顯示成一行,接下來上例子,看看這個神奇的函式如何應用
準備測試資料
SQL> create table test(id number,name varchar2(20));
SQL> insert into test values(1,'a');
SQL> insert into test values(1,'b');
SQL> insert into test values(1,'c');
SQL> insert into test values(2,'d');
SQL> insert into test values(2,'e');
SQL> commit;
效果1 : 行轉列
SQL> select wm_concat(name) from test;
WM_CONCAT(NAME)
-------------------------------------------------------------------------
a,b,c,d,e
效果2: 把結果裡的逗號替換成"|"
SQL> select replace(wm_concat(name),',','|') from test;
REPLACE(WM_CONCAT(NAME),',','|')
-----------------------------------------------------------------------
a|b|c|d|e
效果3:按ID分組合並name
SQL> select id,wm_concat(name) name from test group by id;
ID NAME
---------- ------------------------------
1 a,b,c
2 d,e
懶人擴充套件用法:
案例:我要寫一個檢視,類似"create or replace view as select 欄位1,...欄位50 from tablename" ,基表有50多個欄位,要是靠手工寫太麻煩了,有沒有什麼簡便的方法? 當然有了,看我如果應用wm_concat來讓這個需求變簡單
SQL> select 'create or replace view as select '|| wm_concat(column_name) || ' from dept'from user_tab_columns where table_name='DEPT';
'CREATEORREPLACEVIEWASSELECT'||WM_CONCAT(COLUMN_NAME)||'FROMDEPT'
--------------------------------------------------------------------------------
create or replace view as select DEPTNO,DNAME,LOC from dept
Oracle9i新增 wm_concat函式（轉）
一：
建立type頭
create or replace type string_sum_obj as object (
--聚合函式的實質就是一個物件
sum_string varchar2(4000),
static function ODCIAggregateInitialize(v_self in out string_sum_obj) return number,
--物件初始化
member function ODCIAggregateIterate(self in out string_sum_obj, value in varchar2) return number,
--聚合函式的迭代方法(這是最重要的方法)
member function ODCIAggregateMerge(self in out string_sum_obj, v_next in string_sum_obj) return number,
--當查詢語句並行執行時,才會使用該方法,可將多個並行執行的查詢結果聚合
member function ODCIAggregateTerminate(self in string_sum_obj, return_value out varchar2 ,v_flags in number) return number
--終止聚集函式的處理,返回聚集函式處理的結果.
)
建立type具體
create or replace type body string_sum_obj is
static function ODCIAggregateInitialize(v_self in out string_sum_obj) return number is
begin
v_self := string_sum_obj(null);
return ODCICONST.Success;
end;
member function ODCIAggregateIterate(self in out string_sum_obj, value in varchar2) return number is
begin
/* 連線，解決逗號分隔第一個字母是逗號的問題 */
if not self.sum_string is null then
self.sum_string := self.sum_string ||','|| value;
else
self.sum_string := self.sum_string || value;
end if;
return ODCICONST.Success;
/* 最大值 */
if self.sum_string<value then
self.sum_string:=value;
end if;
/* 最小值 */
if self.sum_string>value then
self.sum_string:=value;
end if;
return ODCICONST.Success;
end;
member function ODCIAggregateMerge(self in out string_sum_obj, v_next in string_sum_obj) return number is
begin
/* 連線 */
self.sum_string := self.sum_string || v_next.sum_string;
return ODCICONST.Success;
/* 最大值 */
if self.sum_string<v_next.sum_string then
self.sum_string:=v_next.sum_string;
end if;
/* 最小值 */
if self.sum_string>v_next.sum_string then
self.sum_string:=v_next.sum_string;
end if;
return ODCICONST.Success;
end;
member function ODCIAggregateTerminate(self in string_sum_obj, return_value out varchar2 ,v_flags in number) return number is
begin
return_value:= self.sum_string;
return ODCICONST.Success;
end;
end;
建立函式
create or replace function wm_concat(value Varchar2) return Varchar2
parallel_enable aggregate using string_sum_obj;
二：
先建立這個型別
create or replace type strcat_type as object (
cat_string varchar2(4000),
static function ODCIAggregateInitialize(cs_ctx In Out strcat_type) return number,
member function ODCIAggregateIterate(self In Out strcat_type,value in varchar2) return number,
member function ODCIAggregateMerge(self In Out strcat_type,ctx2 In Out strcat_type) return number,
member function ODCIAggregateTerminate(self In Out strcat_type,returnValue Out varchar2,flags in number) return number
)
缺少型別體內容：
....
然後建立這個函式
CREATE OR REPLACE FUNCTION strcat(input varchar2 )
RETURN varchar2
PARALLEL_ENABLE AGGREGATE USING strcat_type;
幾個用法：
9i: SYS_CONNECT_BY_PATH 函式
SQL> select id, replace(wmsys.wm_concat(rmak), ',', '') from test group by id;
ID REPLACE(WMSYS.WM_CONCAT(RMAK),
---------- --------------------------------------------------------------------------------
9 timggg
21 littlefff
23 tom
SQL> select * from idtable;
ID NAME
---------- ------------------------------
10 ab
10 bc
10 cd
20 hi
20 ij
20 mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) name from idtable
2 group by id;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab,bc,cd
20 hi,ij,mn
SQL> select id,wmsys.wm_concat(name) over (order by id) name from idtable;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab,bc,cd
10 ab,bc,cd
10 ab,bc,cd
20 ab,bc,cd,hi,ij,mn
20 ab,bc,cd,hi,ij,mn
20 ab,bc,cd,hi,ij,mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (order by id,name) name from idtable;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab
10 ab,bc
10 ab,bc,cd
20 ab,bc,cd,hi
20 ab,bc,cd,hi,ij
20 ab,bc,cd,hi,ij,mn
6 rows selected
個人覺得這個用法比較有趣.
SQL> select id,wmsys.wm_concat(name) over (partition by id) name from idtable;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab,bc,cd
10 ab,bc,cd
10 ab,bc,cd
20 hi,ij,mn
20 hi,ij,mn
20 hi,ij,mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (partition by id,name) name from idtable;
ID NAME
---------- --------------------------------------------------------------------------------
10 ab
10 bc
10 cd
20 hi
20 ij
20 mn
6 rows selected
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