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Oracle SQL精妙SQL语句讲解  

2008-11-28 20:59:52|  分类: 数据库 |  标签: |举报 |字号 订阅

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引用

静心Oracle SQL精妙SQL语句讲解

Oracle SQL精妙SQL语句讲解

转自;http://www.itpub.net/758719.html

--行列转换 行转列

DROP TABLE t_change_lc;

CREATE TABLE t_change_lc (card_code VARCHAR2(3), q NUMBER, bal NUMBER);

INSERT INTO t_change_lc

SELECT '001' card_code, ROWNUM q, trunc(dbms_random.VALUE * 100) bal FROM dual CONNECT BY ROWNUM <= 4

UNION

SELECT '002' card_code, ROWNUM q, trunc(dbms_random.VALUE * 100) bal FROM dual CONNECT BY ROWNUM <= 4;

SELECT * FROM t_change_lc;

SELECT a.card_code,

       SUM(decode(a.q, 1, a.bal, 0)) q1,

       SUM(decode(a.q, 2, a.bal, 0)) q2,

       SUM(decode(a.q, 3, a.bal, 0)) q3,

       SUM(decode(a.q, 4, a.bal, 0)) q4

  FROM t_change_lc a

GROUP BY a.card_code

ORDER BY 1;

--行列转换 列转行

DROP TABLE t_change_cl;

CREATE TABLE t_change_cl AS

SELECT a.card_code,

       SUM(decode(a.q, 1, a.bal, 0)) q1,

       SUM(decode(a.q, 2, a.bal, 0)) q2,

       SUM(decode(a.q, 3, a.bal, 0)) q3,

       SUM(decode(a.q, 4, a.bal, 0)) q4

  FROM t_change_lc a

GROUP BY a.card_code

ORDER BY 1;

SELECT * FROM t_change_cl;

SELECT t.card_code,

       t.rn q,

       decode(t.rn, 1, t.q1, 2, t.q2, 3, t.q3, 4, t.q4) bal

  FROM (SELECT a.*, b.rn

          FROM t_change_cl a,

               (SELECT ROWNUM rn FROM dual CONNECT BY ROWNUM <= 4) b) t

ORDER BY 1, 2;

--行列转换 行转列 合并

DROP TABLE t_change_lc_comma;

CREATE TABLE t_change_lc_comma AS SELECT card_code,'quarter_'||q AS q FROM t_change_lc;

SELECT * FROM t_change_lc_comma;

SELECT t1.card_code, substr(MAX(sys_connect_by_path(t1.q, ';')), 2) q

  FROM (SELECT a.card_code,

               a.q,

               row_number() over(PARTITION BY a.card_code ORDER BY a.q) rn

          FROM t_change_lc_comma a) t1

START WITH t1.rn = 1

CONNECT BY t1.card_code = PRIOR t1.card_code

       AND t1.rn - 1 = PRIOR t1.rn

GROUP BY t1.card_code;

--行列转换 列转行 分割

DROP TABLE t_change_cl_comma;

CREATE TABLE t_change_cl_comma  AS

SELECT t1.card_code, substr(MAX(sys_connect_by_path(t1.q, ';')), 2) q

  FROM (SELECT a.card_code,

               a.q,

               row_number() over(PARTITION BY a.card_code ORDER BY a.q) rn

          FROM t_change_lc_comma a) t1

START WITH t1.rn = 1

CONNECT BY t1.card_code = PRIOR t1.card_code

       AND t1.rn - 1 = PRIOR t1.rn

GROUP BY t1.card_code;

SELECT * FROM t_change_cl_comma;

SELECT t.card_code,

       substr(t.q,

              instr(';' || t.q, ';', 1, rn),

              instr(t.q || ';', ';', 1, rn) - instr(';' || t.q, ';', 1, rn)) q

  FROM (SELECT a.card_code, a.q, b.rn

          FROM t_change_cl_comma a,

               (SELECT ROWNUM rn FROM dual CONNECT BY ROWNUM <= 100) b

         WHERE instr(';' || a.q, ';', 1, rn) > 0) t

ORDER BY 1, 2;

-- 实现一条记录根据条件多表插入

DROP TABLE t_ia_src;

CREATE TABLE t_ia_src AS SELECT 'a'||ROWNUM c1, 'b'||ROWNUM c2 FROM dual CONNECT BY ROWNUM<=5;

DROP TABLE t_ia_dest_1;

CREATE TABLE t_ia_dest_1(flag VARCHAR2(10) , c VARCHAR2(10));

DROP TABLE t_ia_dest_2;

CREATE TABLE t_ia_dest_2(flag VARCHAR2(10) , c VARCHAR2(10));

DROP TABLE t_ia_dest_3;

CREATE TABLE t_ia_dest_3(flag VARCHAR2(10) , c VARCHAR2(10));

SELECT * FROM t_ia_src;

SELECT * FROM t_ia_dest_1;

SELECT * FROM t_ia_dest_2;

SELECT * FROM t_ia_dest_3;

INSERT ALL

WHEN (c1 IN ('a1','a3')) THEN

INTO t_ia_dest_1(flag,c) VALUES(flag1,c2)

WHEN (c1 IN ('a2','a4')) THEN

INTO t_ia_dest_2(flag,c) VALUES(flag2,c2)

ELSE

INTO t_ia_dest_3(flag,c) VALUES(flag1||flag2,c1||c2)

SELECT c1,c2, 'f1' flag1, 'f2' flag2 FROM t_ia_src;

-- 如果存在就更新,不存在就插入用一个语句实现

DROP TABLE t_mg;

CREATE TABLE t_mg(code VARCHAR2(10), NAME VARCHAR2(10));

SELECT * FROM t_mg;

MERGE INTO t_mg a

USING (SELECT 'the code' code, 'the name' NAME FROM dual) b

ON (a.code = b.code)

WHEN MATCHED THEN

  UPDATE SET a.NAME = b.NAME

WHEN NOT MATCHED THEN

  INSERT (code, NAME) VALUES (b.code, b.NAME);

  

-- 抽取/删除重复记录

DROP TABLE t_dup;

CREATE TABLE t_dup AS SELECT 'code_'||ROWNUM code, dbms_random.string('z',5) NAME FROM dual CONNECT BY ROWNUM<=10;

INSERT INTO t_dup SELECT  'code_'||ROWNUM code, dbms_random.string('z',5) NAME FROM dual CONNECT BY ROWNUM<=2;

SELECT * FROM t_dup;

SELECT * FROM t_dup a WHERE a.ROWID <> (SELECT MIN(b.ROWID) FROM t_dup b WHERE a.code=b.code);

SELECT b.code, b.NAME

  FROM (SELECT a.code,

               a.NAME,

               row_number() over(PARTITION BY a.code ORDER BY a.ROWID) rn

          FROM t_dup a) b

WHERE b.rn > 1;

-- IN/EXISTS的不同适用环境

-- t_orders.customer_id有索引

SELECT a.*

  FROM t_employees a

WHERE a.employee_id IN

       (SELECT b.sales_rep_id FROM t_orders b WHERE b.customer_id = 12);

SELECT a.*

  FROM t_employees a

WHERE EXISTS (SELECT 1

          FROM t_orders b

         WHERE b.customer_id = 12

           AND a.employee_id = b.sales_rep_id);

-- t_employees.department_id有索引

SELECT a.*

  FROM t_employees a

WHERE a.department_id = 10

   AND EXISTS

(SELECT 1 FROM t_orders b WHERE a.employee_id = b.sales_rep_id);

SELECT a.*

  FROM t_employees a

WHERE a.department_id = 10

   AND a.employee_id IN (SELECT b.sales_rep_id FROM t_orders b);

   

-- FBI

DROP TABLE t_fbi;

CREATE TABLE t_fbi AS

SELECT ROWNUM rn, dbms_random.STRING('z',10) NAME , SYSDATE + dbms_random.VALUE * 10 dt FROM dual

CONNECT BY ROWNUM <=10;

CREATE INDEX idx_nonfbi ON t_fbi(dt);

DROP INDEX idx_fbi_1;

CREATE INDEX idx_fbi_1 ON t_fbi(trunc(dt));

SELECT * FROM t_fbi WHERE trunc(dt) = to_date('2006-09-21','yyyy-mm-dd') ;

-- 不建议使用

SELECT * FROM t_fbi WHERE to_char(dt, 'yyyy-mm-dd') = '2006-09-21';

-- LOOP中的COMMIT/ROLLBACK

DROP TABLE t_loop PURGE;

create TABLE t_loop AS SELECT * FROM user_objects WHERE 1=2;

SELECT * FROM t_loop;

-- 逐行提交

DECLARE

BEGIN

  FOR cur IN (SELECT * FROM user_objects) LOOP

    INSERT INTO t_loop VALUES cur;

    COMMIT;

  END LOOP;

END;

-- 模拟批量提交

DECLARE

  v_count NUMBER;

BEGIN

  FOR cur IN (SELECT * FROM user_objects) LOOP

    INSERT INTO t_loop VALUES cur;

    v_count := v_count + 1;

    IF v_count >= 100 THEN

      COMMIT;

    END IF;

  END LOOP;

  COMMIT;

END;

-- 真正的批量提交

DECLARE

  CURSOR cur IS

    SELECT * FROM user_objects;

  TYPE rec IS TABLE OF user_objects%ROWTYPE;

  recs rec;

BEGIN

  OPEN cur;

  WHILE (TRUE) LOOP

    FETCH cur BULK COLLECT

      INTO recs LIMIT 100;

    -- forall 实现批量

    FORALL i IN 1 .. recs.COUNT

      INSERT INTO t_loop VALUES recs (i);

    COMMIT;

    EXIT WHEN cur%NOTFOUND;

  END LOOP;

  CLOSE cur;

END;

-- 悲观锁定/乐观锁定

DROP TABLE t_lock PURGE;

CREATE TABLE t_lock AS SELECT 1 ID FROM dual;

SELECT * FROM t_lock;

-- 常见的实现逻辑,隐含bug

DECLARE

  v_cnt NUMBER;

BEGIN

  -- 这里有并发性的bug

  SELECT MAX(ID) INTO v_cnt FROM t_lock;

  -- here for other operation

  v_cnt := v_cnt + 1;

  INSERT INTO t_lock (ID) VALUES (v_cnt);

  COMMIT;

END;

-- 高并发环境下,安全的实现逻辑

DECLARE

  v_cnt NUMBER;

BEGIN

  -- 对指定的行取得lock

  SELECT ID INTO v_cnt FROM t_lock WHERE ID=1 FOR UPDATE;

  -- 在有lock的情况下继续下面的操作

  SELECT MAX(ID) INTO v_cnt FROM t_lock;

  -- here for other operation

  v_cnt := v_cnt + 1;

  INSERT INTO t_lock (ID) VALUES (v_cnt);

  COMMIT; --提交并且释放lock

END;

-- 硬解析/软解析

DROP TABLE t_hard PURGE;

CREATE TABLE t_hard (ID INT);

SELECT * FROM t_hard;

DECLARE

  sql_1   VARCHAR2(200);

BEGIN

  -- hard parse

  -- java中的同等语句是 Statement.execute()

  FOR i IN 1 .. 1000 LOOP

    sql_1 := 'insert into t_hard(id) values(' || i || ')';

    EXECUTE IMMEDIATE sql_1;

  END LOOP;

  COMMIT;

  -- soft parse

  --java中的同等语句是 PreparedStatement.execute()

  sql_1   := 'insert into t_hard(id) values(:id)';

  FOR i IN 1 .. 1000 LOOP

    EXECUTE IMMEDIATE sql_1

      USING i;

  END LOOP;

  COMMIT;

END;

-- 正确的分页算法

SELECT *

  FROM (SELECT a.*, ROWNUM rn

          FROM (SELECT * FROM t_employees ORDER BY first_name) a

         WHERE ROWNUM <= 500)

WHERE rn > 480 ;

-- 分页算法(why not this one)

SELECT a.*, ROWNUM rn

  FROM (SELECT * FROM t_employees ORDER BY first_name) a

WHERE ROWNUM <= 500 AND ROWNUM > 480;

-- 分页算法(why not this one)

SELECT b.*

  FROM (SELECT a.*, ROWNUM rn

          FROM t_employees a

         WHERE ROWNUM < = 500

         ORDER BY first_name) b

WHERE b.rn > 480;

-- OLAP

-- 小计合计

SELECT CASE

         WHEN a.deptno IS NULL THEN

          '合计'

         WHEN a.deptno IS NOT NULL AND a.empno IS NULL THEN

          '小计'

         ELSE

          '' || a.deptno

       END deptno,

       a.empno,

       a.ename,

       SUM(a.sal) total_sal

  FROM scott.emp a

GROUP BY GROUPING SETS((a.deptno),(a.deptno, a.empno, a.ename),());

-- 分组排序

SELECT a.deptno,

       a.empno,

       a.ename,

       a.sal,

       -- 可跳跃的rank

       rank() over(PARTITION BY a.deptno ORDER BY a.sal DESC) r1,

       -- 密集型rank

       dense_rank() over(PARTITION BY a.deptno ORDER BY a.sal DESC) r2,

       -- 不分组排序

       rank() over(ORDER BY sal DESC) r3

  FROM scott.emp a

  ORDER BY a.deptno,a.sal DESC;

  

-- 当前行数据和前/后n行的数据比较

SELECT a.empno,

       a.ename,

       a.sal,

       -- 上面一行

       lag(a.sal) over(ORDER BY a.sal DESC) lag_1,

       -- 下面三行

       lead(a.sal, 3) over(ORDER BY a.sal DESC) lead_3

  FROM scott.emp a

ORDER BY a.sal DESC;

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