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  • sql 语句集合

    1.取最新的一条记录

    Select id
    From (select id ,RANK() over(PARTITION BY id  order by Savetime desc) as RN
    From table_Name
    ) s where RN=1

    2.递归查找 start with connect by prior 

    ----从子节点父节点

    select * from table_name where  start with id = '1'  connect by  prior parent_id =id;

    ----从父节点子节点

    select * from table_name  start with id='1' connect by prior id=parentid

    ---- CONNECT_BY_ROOT 返回当前节点的最顶端节点 

    ----CONNECT_BY_ISLEAF 判断是否为叶子节点,如果这个节点下面有子节点,则不为叶子节点 
    ----LEVEL 伪列表示节点深度 
    ----SYS_CONNECT_BY_PATH函数显示详细路径,并用“/”分隔

    SELECT (RPAD(' ', 2*(LEVEL-1), '' ) || COMPANY) COMPANY_NAME, 

     

    CONNECT_BY_ROOT COMPANY, 

    CONNECT_BY_ISLEAF, LEVEL , 

    SYS_CONNECT_BY_PATH(COMPANY, '/') 

     FROM TB_COMPANY  

    START WITH UP_COMPANYID IS NULL  CONNECT BY PRIOR COMPANY_ID = UP_COMPANYID;  

     

    3  declare  cursor

    declare v_table_en_name varchar2(500);
    v_Sql varchar2(1000);
    cursor mycur IS
    SELECT tbphyisename FROM tablename  ;
    begin
    OPEN mycur; --OPEN CURSOR
    FETCH mycur INTO v_table_en_name;--FETCH ONE Record TO RECORD FROM CURSOR
    WHILE mycur%FOUND LOOP -- LOOP WHEN HAS RECORDS
    v_Sql := 'drop table '|| v_table_en_name;
    EXECUTE IMMEDIATE v_Sql ;
    FETCH mycur INTO v_table_en_name;--FETCH ONE Record TO RECORD FROM CURSOR AGAIN
    END LOOP; --END LOOP
    CLOSE mycur;--CLOSE CURSOR
    end;

    4. 查数据库当前连接数

    select count(*) from v$session

    --当前连接情况

    select sid,serial#,username,status,schemaname,osuser,machine,port,terminal,program,type,module,action,event,service_name from v$session 

    --当前的进程

    select * from v$process

    --允许的最大连接数 (v$parameter 参数配置表)

    select value from v$parameter where name ='session'

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  • 原文地址:https://www.cnblogs.com/benhua/p/7795125.html
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