- 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)
NAMEFROM dual CONNECT BY ROWNUM<=2;
SELECT * FROM t_dup;
SELECT * FROM t_dup aWHERE 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_nonfbiON t_fbi(dt);
DROP INDEX idx_fbi_1;
CREATE INDEX idx_fbi_1 ON t_fbi(trunc(dt));
SELECT * FROM t_fbiWHERE 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;