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Oracle SQL精妙SQL语句讲解

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发表于 2016-1-18 17:05:39 | 显示全部楼层 |阅读模式

 --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http://blog.knowsky.com/
  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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发表于 2018-1-17 18:06:50 | 显示全部楼层
佩服你,能发这么好的帖子,厉害
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发表于 2018-1-28 15:40:50 | 显示全部楼层
很不错的帖子,又学到了,力挺
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发表于 2018-5-16 13:34:19 | 显示全部楼层
抱走~老好人
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发表于 2018-8-3 13:00:34 | 显示全部楼层
楼主是好人哪,感谢分享,太棒了!
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发表于 2018-12-21 21:01:46 | 显示全部楼层
大神啊!豁然开朗。。。。。。
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发表于 2019-2-20 15:47:35 | 显示全部楼层
谢谢您的分享!
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