DBAlife » SQL

用SQL处理多行汇聚问题

skywalker — Wed, 03 Feb 2010 04:50:12 +0000

表结构如下：
NAME Null Type
------------------------ --------- -----
N_SEC_CODE NOT NULL CHAR(6)
C_RESEARCHER_CODE NOT NULL VARCHAR2(20)

此表保存了“股票”与“研究员”的对应关系数据，一般而言，对于同一只股票而言，可能有多个研究员对其进行跟踪研究。所以目前遇到一个要求，需查询出每只股票和对应的研究员（研究员代码间，使用逗号分隔）。

例如有如下数据：
000297 chenpeng
000297 liusu
合并处理后需显示为：
000297 chenpeng,liusu

多行数据汇总聚一行，只需要把SQL中“n_sec_code”换为你的用来汇总的列，“c_researcher_code”替换为需合并文本的列，“m_researcher_stock_rel”替换为你的表名

SELECT n_sec_code,
TRANSLATE (LTRIM (text, '/'), '*/', '*,') researcherList
   FROM
(SELECT ROW_NUMBER () OVER (PARTITION BY n_sec_code ORDER BY n_sec_code, lvl DESC) rn,
    n_sec_code                                                                         ,
    text
     FROM
    (SELECT n_sec_code,
      LEVEL lvl       ,
      SYS_CONNECT_BY_PATH (c_researcher_code,'/') text
       FROM
      (SELECT n_sec_code                      ,
        c_researcher_code AS c_researcher_code,
        ROW_NUMBER () OVER (PARTITION BY n_sec_code ORDER BY n_sec_code,c_researcher_code) x
         FROM m_researcher_stock_rel
     ORDER BY n_sec_code,
        c_researcher_code
      ) a CONNECT BY n_sec_code = PRIOR n_sec_code
    AND x - 1                   = PRIOR x
    )
)
WHERE rn = 1
ORDER BY n_sec_code;

sqlplus增强设置

skywalker — Thu, 24 Sep 2009 04:11:05 +0000

更强的编辑器

sqlplus可以与vi整合，在sqlplus中调用vi编辑器。方法是在sqlplus中执行define_editor='vi'，或将define_editor='vi'添加到/product/10.2/sqlplus/admin/glogin.sql文件中。

之后再登录sqlplus，可以输入edit命令编辑上一次执行的sql。

更人性化的提示符

在glogin.sql文件中添加：

set termout off
default gname=idle
column global_name new_value gname
SELECT lower(USER) || '@' ||upper(instance_name)||'('||nvl(UTL_INADDR.GET_HOST_ADDRESS, SYS_CONTEXT('userenv', 'ip_address'))||')' GLOBAL_NAME FROM v$instance;
set sqlprompt '&gname> '
set termout on

这样每次登录SQLPLUS提示符会自动更改为“当前用户名@实例名(IP地址)> ”的形式。

10g以下版本在登录后切换用户的情况下，提示符不能自动更新。

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undo相关的sql

skywalker — Thu, 02 Jul 2009 03:36:41 +0000

查UNDO统计信息语句：
SELECT TO_CHAR(BEGIN_TIME,'HH24:MI:SS') BEGIN_TIME,
TO_CHAR(END_TIME,'HH24:MI:SS') END_TIME,
UNDOBLKS
FROM V$UNDOSTAT;
-------------------------------------------结果--------------------------------------------------------------
begin_time end_time undoblocks
9:48:30 9:53:07 76293
9:38:30 9:48:30 143670
9:28:30 9:38:30 130921
9:18:30 9:28:30 122500
9:08:30 9:18:30 149030
8:58:30 9:08:30 144586
8:48:30 8:58:30 108095
8:38:30 8:48:30 63533
8:28:30 8:38:30 72819
8:18:30 8:28:30 23321
8:08:30 8:18:30 2026
7:58:30 8:08:30 15480
7:48:30 7:58:30 91111
7:38:30 7:48:30 15810
7:28:30 7:38:30 56922
7:18:30 7:28:30 30449
7:08:30 7:18:30 6096
6:58:30 7:08:30 15022
6:48:30 6:58:30 91904
6:38:30 6:48:30 38794
6:28:30 6:38:30 111884
----------------------------------------------------------------------------------------------------------
查UNDO表空间的使用情况：
select
  a.a1 表空间名,
  substr(b.b2/1024/1024/1024,1,5) 表空间大小G,
  substr(a.a2/1024/1024/1024,1,5) 剩余表空间G,
  substr((b.b2-a.a2)/1024/1024/1024,1,5) 实际使用表空间G,
  substr((b.b2-a.a2)/b.b2*100,1,5) 利用率,
  c.c2 类型,
  c.c3 区管理方式
  from
  (select tablespace_name a1,sum(Nvl(bytes,0)) a2 from dba_free_space group by tablespace_name) a,
  (select tablespace_name b1,sum(bytes) b2 from dba_data_files group by tablespace_name) b,
  (select tablespace_name c1,contents c2,extent_management c3 from dba_tablespaces) c
  where a.a1=b.b1 and b.b1=c.c1
  order by c.c2 desc
-------------------------------------------------结果--------------------------------------------------------------------
表空间名表空间大小(G) 剩余(G) 使用利用率表空间类型管理方式
UNDOTBS1 17.24 1.124 16.12 93.48 UNDO LOCAL
----------------------------------------------------------------------------------------------------------------------------
建议UNDO峰值：
select ur undo_retention,dbs db_block_size, ((ur * (ups * dbs)) + (dbs * 24)) / 1024 / 1024 as "M_bytes"
from (select value as ur from v$parameter where name = 'undo_retention'),
   (select (undoblks / ((end_time - begin_time) * 86400)) ups from v$undostat where undoblks in (select max(undoblks) from  v$undostat ) ),
   (select value as dbs from v$parameter where name = 'db_block_size');
----------------------------------------------结果------------------------------------------------------------------
undo_retention db_block_size M_bytes
10800                         8192             33,376.96875

表空间使用状况查询

skywalker — Thu, 25 Sep 2008 01:16:25 +0000

SELECT D.TABLESPACE_NAME ,
SPACE "SUM_SPACE(M)" ,
BLOCKS SUM_BLOCKS ,
SPACE -NVL(FREE_SPACE,0) "USED_SPACE(M)" ,
ROUND((1-NVL(FREE_SPACE,0)/SPACE)*100,2) "USED_RATE(%)",
FREE_SPACE "FREE_SPACE(M)"
FROM
(SELECT TABLESPACE_NAME ,
ROUND(SUM(BYTES)/(1024*1024),2) SPACE,
SUM(BLOCKS) BLOCKS
FROM DBA_DATA_FILES
GROUP BY TABLESPACE_NAME
) D ,
(SELECT TABLESPACE_NAME,
ROUND(SUM(BYTES)/(1024*1024),2) FREE_SPACE
FROM DBA_FREE_SPACE
GROUP BY TABLESPACE_NAME
) F
WHERE D.TABLESPACE_NAME = F.TABLESPACE_NAME(+)

UNION ALL --if have tempfile

SELECT D.TABLESPACE_NAME ,
SPACE "SUM_SPACE(M)" ,
BLOCKS SUM_BLOCKS ,
USED_SPACE "USED_SPACE(M)" ,
ROUND(NVL(USED_SPACE,0)/SPACE*100,2) "USED_RATE(%)",
NVL(FREE_SPACE,0) "FREE_SPACE(M)"
FROM
(SELECT TABLESPACE_NAME ,
ROUND(SUM(BYTES)/(1024*1024),2) SPACE,
SUM(BLOCKS) BLOCKS
FROM DBA_TEMP_FILES
GROUP BY TABLESPACE_NAME
) D ,
(SELECT TABLESPACE_NAME ,
ROUND(SUM(BYTES_USED)/(1024*1024),2) USED_SPACE,
ROUND(SUM(BYTES_FREE)/(1024*1024),2) FREE_SPACE
FROM V$TEMP_SPACE_HEADER
GROUP BY TABLESPACE_NAME
) F
WHERE D.TABLESPACE_NAME = F.TABLESPACE_NAME(+)

模糊查询like '%XX%' 的优化一例

skywalker — Fri, 19 Sep 2008 06:47:33 +0000

sql中的like '%xx%'模糊查询无法走索引，影响执行速度。经测试itpub版主ifree的index_ffs+rowid方法比较有效，记录一下。

这里是示例：

scott@ORCL> CREATE INDEX SCOTT.i_dept_name
2 ON SCOTT.DEPT(DNAME)
3 ;

Index created.

scott@ORCL> Analyze Table SCOTT.DEPT Compute Statistics ;

Table analyzed.

scott@ORCL> select * from scott.dept where
  2  rowid in (
  3  select /*+ index_ffs(a i_dept_dname) */
  4  rowid from scott.dept a where dname like '%A%')
  5  ;

这个方法要求like查询出的记录不能太多，在我的应用中，这一方法使sql效率提高了近10倍。

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Tags: sql, 优化, turning, like, 模糊查询

等待事件相关的SQL

skywalker — Wed, 30 Jul 2008 05:16:36 +0000

--求等待事件及其对应的latch

col event format a32
col name format a32
select sid,event,p1 as file_id, p2 as "block_id/latch", p3 as blocks,l.name
from v$session_wait sw,v$latch l
where event not like '%SQL%' and event not like '%rdbms%'
and event not like '%mon%' and sw.p2 = l.latch#(+);
--求等待事件及其热点对象

col owner format a18
col segment_name format a32
col segment_type format a32
select owner,segment_name,segment_type
from dba_extents
where file_id = &file_id and &block_id between block_id
and block_id + &blocks - 1;
--综合以上两条sql，同时显示latch及热点对象(速度较慢)

select sw.sid,event,l.name,de.segment_name
from v$session_wait sw,v$latch l,dba_extents de
where event not like '%SQL%' and event not like '%rdbms%'
and event not like '%mon%' and sw.p2 = l.latch#(+) and sw.p1 = de.file_id(+) and p2 between de.block_id and de.block_id + de.blocks - 1;
--如果是非空闲等待事件，通过等待会话的sid可以求出该会话在执行的sql

select sql_text
from v$sqltext_with_newlines st,v$session se
where st.address=se.sql_address and st.hashvalue=se.sql_hash_value
and se.sid =&wait_sid order by piece;