Oracle Sql技巧 Upsert, Multitable Insert, Undrop

近期参加OCP培训，讲师说的太快，之前一直是SQLSERVER，很多东西要恶补了。

UpSert功能：

MERGE <hint> INTO <table_name>
USING <table_view_or_query>
ON (<condition>)
WHEN MATCHED THEN <update_clause>
WHEN NOT MATCHED THEN <insert_clause>;

multiTable Inserts功能：

Multitable inserts allow a single INSERT INTO .. SELECT statement to conditionally, or non-conditionally, insert into multiple tables. This
statement reduces table scans and PL/SQL code necessary for performing multiple conditional inserts compared to previous versions. It's
main use is for the ETL process in data warehouses where it can be parallelized and/or convert non-relational data into a relational format:

-- Unconditional insert into ALL tables

INSERT ALL
INTO sal_history VALUES(empid,hiredate,sal)
INTO mgr_history VALUES(empid,mgr,sysdate) 
SELECT employee_id EMPID, hire_date HIREDATE, salary SAL, manager_id MGR
FROM employees WHERE employee_id > 200;

-- Pivoting insert to split non-relational data

INSERT ALL
INTO Sales_info VALUES (employee_id,week_id,sales_MON)
INTO Sales_info VALUES (employee_id,week_id,sales_TUE)
INTO Sales_info VALUES (employee_id,week_id,sales_WED)
INTO Sales_info VALUES (employee_id,week_id,sales_THUR)
INTO Sales_info VALUES (employee_id,week_id, sales_FRI)
SELECT EMPLOYEE_ID, week_id, sales_MON, sales_TUE,
sales_WED, sales_THUR,sales_FRI 
FROM Sales_source_data;

-- Conditionally insert into ALL tables

INSERT ALL
WHEN SAL>10000 THEN
INTO sal_history VALUES(EMPID,HIREDATE,SAL)
WHEN MGR>200 THEN
INTO mgr_history VALUES(EMPID,MGR,SYSDATE)
SELECT employee_id EMPID, hire_date HIREDATE, salary SAL, manager_id MGR
FROM employees WHERE employee_id > 200;

-- Insert into the FIRST table with a matching condition

INSERT FIRST
WHEN SAL > 25000THEN
INTO special_sal VALUES(DEPTID,SAL)
WHEN HIREDATE like ('%00%') THEN
INTO hiredate_history_00 VALUES(DEPTID,HIREDATE)
WHEN HIREDATE like ('%99%') THEN 
INTO hiredate_history_99 VALUES(DEPTID,HIREDATE)
ELSE
INTO hiredate_history VALUES(DEPTID, HIREDATE)
SELECT department_id DEPTID, SUM(salary) SAL,
MAX(hire_date) HIREDATE
FROM employees GROUP BY department_id;

The restrictions on multitable INSERTs are:

Multitable inserts can only be performed on tables, not on views or materialized views.
You cannot perform a multitable insert via a DB link.
You cannot perform multitable inserts into nested tables.
The sum of all the INTO columns cannot exceed 999.
Sequences cannot be used in the subquery of the multitable insert statement.

Undrop功能

From Oracle 10g a table can be "undropped". Example:

SQL> FLASHBACK TABLE emp TO BEFORE DROP;

Flashback complete.