多行轉字符串
這個比較簡單,用||或concat函數可以實現select concat(id,username) str from app_user select id||username str from app_user
首先讓我們來看看這個神奇的函數wm_concat(列名),該函數可以把列值以","號分隔起來,並顯示成一行,接下來上例子,看看這個神奇的函數如何應用准備測試數據
create table test(id number,name varchar2(20)); insert into test values(1,'a'); insert into test values(1,'b'); insert into test values(1,'c'); insert into test values(2,'d'); insert into test values(2,'e');
select wm_concat(name) name from test;
select replace(wm_concat(name),',','|') from test;
select id,wm_concat(name) name from test group by id;
-------- 適用范圍:8i,9i,10g及以後版本 ( MAX + DECODE ) select id, max(decode(rn, 1, name, null)) || max(decode(rn, 2, ',' || name, null)) || max(decode(rn, 3, ',' || name, null)) str from (select id,name,row_number() over(partition by id order by name) as rn from test) t group by id order by 1; -------- 適用范圍:8i,9i,10g及以後版本 ( ROW_NUMBER + LEAD ) select id, str from (select id,row_number() over(partition by id order by name) as rn,name || lead(',' || name, 1) over(partition by id order by name) || lead(',' || name, 2) over(partition by id order by name) || lead(',' || name, 3) over(partition by id order by name) as str from test) where rn = 1 order by 1; -------- 適用范圍:10g及以後版本 ( MODEL ) select id, substr(str, 2) str from test model return updated rows partition by(id) dimension by(row_number() over(partition by id order by name) as rn) measures (cast(name as varchar2(20)) as str) rules upsert iterate(3) until(presentv(str[iteration_number+2],1,0)=0) (str[0] = str[0] || ',' || str[iteration_number+1]) order by 1; -------- 適用范圍:8i,9i,10g及以後版本 ( MAX + DECODE ) select t.id id,max(substr(sys_connect_by_path(t.name,','),2)) str from (select id, name, row_number() over(partition by id order by name) rn from test) t start with rn = 1 connect by rn = prior rn + 1 and id = prior id group by t.id;</span>
/** 這裡的表名默認區分大小寫 */ select 'create or replace view as select '|| wm_concat(column_name) || ' from APP_USER' sqlStr from user_tab_columns where table_name='APP_USER';
利用系統表方式查詢
select * from user_tab_columns
在Oracle 11g中,Oracle 又增加了2個查詢:pivot(行轉列) 和unpivot(列轉行)
參考:http://blog.csdn.net/tianlesoftware/article/details/7060306、http://www.oracle.com/technetwork/cn/articles/11g-pivot-101924-zhs.html
google 一下,網上有一篇比較詳細的文檔:http://www.oracle-developer.net/display.php?id=506
create table demo(id int,name varchar(20),nums int); ---- 創建表 insert into demo values(1, '蘋果', 1000); insert into demo values(2, '蘋果', 2000); insert into demo values(3, '蘋果', 4000); insert into demo values(4, '橘子', 5000); insert into demo values(5, '橘子', 3000); insert into demo values(6, '葡萄', 3500); insert into demo values(7, '芒果', 4200); insert into demo values(8, '芒果', 5500);
分組查詢 (當然這是不符合查詢一條數據的要求的)
select name, sum(nums) nums from demo group by name
行轉列查詢
select * from (select name, nums from demo) pivot (sum(nums) for name in ('蘋果' 蘋果, '橘子', '葡萄', '芒果'));
注意: pivot(聚合函數 for 列名 in(類型)) ,其中 in(‘’) 中可以指定別名,in中還可以指定子查詢,比如 select distinct code from customers
當然也可以不使用pivot函數,等同於下列語句,只是代碼比較長,容易理解
select * from (select sum(nums) 蘋果 from demo where name='蘋果'),(select sum(nums) 橘子 from demo where name='橘子'), (select sum(nums) 葡萄 from demo where name='葡萄'),(select sum(nums) 芒果 from demo where name='芒果');
創建表和數據
create table Fruit(id int,name varchar(20), Q1 int, Q2 int, Q3 int, Q4 int); insert into Fruit values(1,'蘋果',1000,2000,3300,5000); insert into Fruit values(2,'橘子',3000,3000,3200,1500); insert into Fruit values(3,'香蕉',2500,3500,2200,2500); insert into Fruit values(4,'葡萄',1500,2500,1200,3500); select * from Fruit
列轉行查詢
select id , name, jidu, xiaoshou from Fruit unpivot (xiaoshou for jidu in (q1, q2, q3, q4) )注意: unpivot沒有聚合函數,xiaoshou、jidu字段也是臨時的變量
同樣不使用unpivot也可以實現同樣的效果,只是sql語句會很長,而且執行速度效率也沒有前者高
select id, name ,'Q1' jidu, (select q1 from fruit where id=f.id) xiaoshou from Fruit f union select id, name ,'Q2' jidu, (select q2 from fruit where id=f.id) xiaoshou from Fruit f union select id, name ,'Q3' jidu, (select q3 from fruit where id=f.id) xiaoshou from Fruit f union select id, name ,'Q4' jidu, (select q4 from fruit where id=f.id) xiaoshou from Fruit f
pivot 操作中的另一個子句 XML 可用於解決此問題。該子句允許您以 XML 格式創建執行了 pivot 操作的輸出,在此輸出中,您可以指定一個特殊的子句 ANY 而非文字值
示例如下:
select * from ( select name, nums as "Purchase Frequency" from demo t ) pivot xml ( sum(nums) for name in (any) )
Pivot 為 SQL 語言增添了一個非常重要且實用的功能。您可以使用 pivot 函數針對任何關系表創建一個交叉表報表,而不必編寫包含大量 decode 函數的令人費解的、不直觀的代碼。同樣,您可以使用 unpivot 操作轉換任何交叉表報表,以常規關系表的形式對其進行存儲。Pivot 可以生成常規文本或 XML 格式的輸出。如果是 XML 格式的輸出,您不必指定 pivot 操作需要搜索的值域。