知识大全 OracleSQL精妙SQL语句讲解

Posted 2022-07-16 语句

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　　行列转换行转列

　　DROP TABLE t_change_lc;

　　CREATE TABLE t_change_lc (card_code VARCHAR ( ) q NUMBER bal NUMBER);

　　INSERT INTO t_change_lc

　　SELECT card_code ROWNUM q trunc(dbms_random VALUE * ) bal FROM dual CONNECT BY ROWNUM <=

　　UNION

　　SELECT card_code ROWNUM q trunc(dbms_random VALUE * ) bal FROM dual CONNECT BY ROWNUM <= ;

　　SELECT * FROM t_change_lc;

　　SELECT a card_code

　　SUM(decode(a q a bal )) q

　　FROM t_change_lc a

　　GROUP BY a card_code

　　ORDER BY ;

　　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 a bal )) q

　　FROM t_change_lc a

　　GROUP BY a card_code

　　ORDER BY ;

　　SELECT * FROM t_change_cl;

　　SELECT t card_code

　　t rn q

　　decode(t rn t q t q t q t q ) bal

　　FROM (SELECT a * b rn

　　FROM t_change_cl a

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

　　ORDER BY ;

　　行列转换行转列合并

　　DROP TABLE t_change_lc_ma;

　　CREATE TABLE t_change_lc_ma AS SELECT card_code quarter_ ||q AS q FROM t_change_lc;

　　SELECT * FROM t_change_lc_ma;

　　SELECT t card_code substr(MAX(sys_connect_by_path(t q ; )) ) 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_ma a) t

　　START WITH t rn =

　　CONNECT BY t card_code = PRIOR t card_code

　　AND t rn = PRIOR t rn

　　GROUP BY t card_code;

　　行列转换列转行分割

　　DROP TABLE t_change_cl_ma;

　　CREATE TABLE t_change_cl_ma AS

　　SELECT t card_code substr(MAX(sys_connect_by_path(t q ; )) ) 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_ma a) t

　　START WITH t rn =

　　CONNECT BY t card_code = PRIOR t card_code

　　AND t rn = PRIOR t rn

　　GROUP BY t card_code;

　　SELECT * FROM t_change_cl_ma;

　　SELECT t card_code

　　substr(t q

　　instr( ; || t q ; rn)

　　instr(t q || ; ; rn) instr( ; || t q ; rn)) q

　　FROM (SELECT a card_code a q b rn

　　FROM t_change_cl_ma a

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

　　WHERE instr( ; || a q ; rn) > ) t

　　ORDER BY ;

　　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 c b ||ROWNUM c FROM dual CONNECT BY ROWNUM<= ;

　　DROP TABLE t_ia_dest_ ;

　　CREATE TABLE t_ia_dest_ (flag VARCHAR ( ) c VARCHAR ( ));

　　DROP TABLE t_ia_dest_ ;

　　CREATE TABLE t_ia_dest_ (flag VARCHAR ( ) c VARCHAR ( ));

　　DROP TABLE t_ia_dest_ ;

　　CREATE TABLE t_ia_dest_ (flag VARCHAR ( ) c VARCHAR ( ));

　　SELECT * FROM t_ia_src;

　　SELECT * FROM t_ia_dest_ ;

　　INSERT ALL

　　WHEN (c IN ( a a )) THEN

　　INTO t_ia_dest_ (flag c) VALUES(flag c )

　　WHEN (c IN ( a a )) THEN

　　INTO t_ia_dest_ (flag c) VALUES(flag c )

　　ELSE

　　INTO t_ia_dest_ (flag c) VALUES(flag ||flag c ||c )

　　SELECT c c f flag f flag 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 VARCHAR ( ) NAME VARCHAR ( ));

　　SELECT * FROM t_mg;

　　MERGE INTO t_mg a

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

　　ON (de = de)

　　WHEN MATCHED THEN

　　UPDATE SET a NAME = b NAME

　　WHEN NOT MATCHED THEN

　　INSERT (code NAME) VALUES (de 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 ) NAME FROM dual CONNECT BY ROWNUM<= ;

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

　　SELECT * FROM t_dup;

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

　　SELECT de b NAME

　　FROM (SELECT de

　　a NAME

　　row_number() over(PARTITION BY de ORDER BY a ROWID) rn

　　FROM t_dup a) b

　　WHERE b rn > ;

　　 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 = );

　　SELECT a *

　　FROM t_employees a

　　WHERE EXISTS (SELECT

　　FROM t_orders b

　　WHERE b customer_id =

　　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 =

　　AND EXISTS

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

　　SELECT a *

　　FROM t_employees a

　　WHERE a department_id =

　　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 ) NAME SYSDATE + dbms_random VALUE * dt FROM dual

　　CONNECT BY ROWNUM <= ;

　　CREATE INDEX idx_nonfbi ON t_fbi(dt);

　　DROP INDEX idx_fbi_ ;

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

　　SELECT * FROM t_fbi WHERE trunc(dt) = to_date( yyyy mm dd ) ;

　　不建议使用

　　SELECT * FROM t_fbi WHERE to_char(dt yyyy mm dd ) = ;

　　 LOOP中的MIT/ROLLBACK

　　DROP TABLE t_loop PURGE;

　　create TABLE t_loop AS SELECT * FROM user_objects WHERE = ;

　　SELECT * FROM t_loop;

　　逐行提交

　　DECLARE

　　BEGIN

　　FOR cur IN (SELECT * FROM user_objects) LOOP

　　INSERT INTO t_loop VALUES cur;

　　MIT;

　　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 + ;

　　IF v_count >= THEN

　　MIT;

　　END IF;

　　END LOOP;

　　MIT;

　　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 ;

　　 forall 实现批量

　　FORALL i IN recs COUNT

　　INSERT INTO t_loop VALUES recs (i);

　　MIT;

　　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 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 + ;

　　INSERT INTO t_lock (ID) VALUES (v_cnt);

　　MIT;

　　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= 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 + ;

　　INSERT INTO t_lock (ID) VALUES (v_cnt);

　　MIT; 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_ VARCHAR ( );

　　BEGIN

　　 hard parse

　　 java中的同等语句是 Statement execute()

　　FOR i IN LOOP

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

　　EXECUTE IMMEDIATE sql_ ;

　　END LOOP;

　　MIT;

　　 soft parse

　　 java中的同等语句是 PreparedStatement execute()

　　sql_ := insert into t_hard(id) values(:id) ;

　　FOR i IN LOOP

　　EXECUTE IMMEDIATE sql_

　　USING i;

　　END LOOP;

　　MIT;

　　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 <= )

　　WHERE rn > ;

　　分页算法(why not this one)

　　SELECT a * ROWNUM rn

　　FROM (SELECT * FROM t_employees ORDER BY first_name) a

　　WHERE ROWNUM <= AND ROWNUM > ;

　　分页算法(why not this one)

　　SELECT b *

　　FROM (SELECT a * ROWNUM rn

　　FROM t_employees a

　　WHERE ROWNUM < =

　　ORDER BY first_name) b

　　WHERE b rn > ;

　　 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) r

　　密集型rank

　　dense_rank() over(PARTITION BY a deptno ORDER BY a sal DESC) r

　　不分组排序

　　rank() over(ORDER BY sal DESC) r

　　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_

　　下面三行

　　lead(a sal ) over(ORDER BY a sal DESC) lead_

　　FROM scott emp a

cha138/Article/program/Oracle/201311/16728