5个SQL核心

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5     SELECT <columnlist>

1     FROM <source objectlist>

1.1   FROM <left source object><join type>

    JOIN <right source object>ON <on predicates(谓词，判断)>

2     WHERE <wherepredicates>

3    GROUP BY <group byexpression(s)>

4    HAVING <having predicates>

6    ORDER BY <order by list>

1、交叉联结，也称笛卡尔积；

2、内联结；

3、外联结。

将执行FROM和WHERE后得到的经过筛选后的结果集进行聚合。结果集按照GROUPBY子句列出的表达式进行分组，来为每一个分组得出一行汇总结果。

可按照FROM子句中所列出对象的任意字段进行分组，即使并不在结果中显示该列。但SELECT子句列表中的任何非聚合字段都必须包含在GROUPBY表达式中。 

GROUPBY还可包含两个附加运算：ROLLUP,CUBE。ROLLUP产生部分求和值，CUBE求得交互分类值。

INSERT ALL

WHEN sum_orders < 10000 THEN

INTO small_customers

WHEN sum_orders >=   10000 AND sum_orders <100000THEN

INTO medium_customers

ELSE

INTO large_customers

SELECT customer_id,sum(order_total) sum_orders

FROM orders

GROUP BY customer_id;

UPDATE (SELECT e1.salary,e2.salary new_sal

FROM employees e1,employees2 e2

WHERE e1.employee_id=e2.employee_id

AND e1.department_id=90)

SET salary = new_sal;

UPDATE employees

SET (salary,commission_pct) = (SELECT employees2.salary, .10comm_pct

  FROM employees2

   WHEREemployee2.employee_id=employees.employee_id

    AND employees.salary != employees2.salary)

WHERE department_id=90;

DELETE FROM employees2

WHERE department_id = 90;

DELETE FROM (SELECT * FROM employees2 WHERE department_id =90);

DELETE FROM employees2

WHERE department_id IN (SELECT department_id

     FROM departments

      WHERE department_name =‘Excutive‘);

MERGE <hint>

INTO <tablename>
USING <table_view or query>
ON (<condition>)
WHEN MATCHED THEN <update_clause>
DELETE <where_clause>
WHEN NOT MATCHED THEN <insert_clause>

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5个SQL核心

标签：style   code   http   color   com   使用   

原文地址：http://www.cnblogs.com/shadowwalker/p/3800270.html