SQL

sql语句执行顺序

(8) SELECT

(9)DISTINCT

(1) FROM

(3) JOIN

(2) ON

(4) WHERE

(5) GROUP BY

(6) WITH {CUBE|ROLLUP}

(7) HAVING

(10) ORDER BY

(11) LIMIT

(1) FROM:对FROM子句中的左表和右表执行笛卡儿积，产生虚拟表VT1;

(2) ON: 对虚拟表VT1进行ON筛选，只有那些符合的行才被插入虚拟表VT2;

(3) JOIN: 如果指定了OUTER JOIN(如LEFT OUTER JOIN、RIGHT OUTER JOIN)，那么保留表中未匹配的行作为外部行添加到虚拟表VT2，产生虚拟表VT3。

如果FROM子句包含两个以上的表，则对上一个连接生成的结果表VT3和下一个表重复执行步骤1~步骤3，直到处理完所有的表;

(4) WHERE: 对虚拟表VT3应用WHERE过滤条件，只有符合的记录才会被插入虚拟表VT4;

(5) GROUP By: 根据GROUP BY子句中的列，对VT4中的记录进行分组操作，产生VT5;

(6) CUBE|ROllUP: 对VT5进行CUBE或ROLLUP操作，产生表VT6;

(7) HAVING: 对虚拟表VT6应用HAVING过滤器，只有符合的记录才会被插入到VT7;

(8) SELECT: 第二次执行SELECT操作，选择指定的列，插入到虚拟表VT8中;

(9) DISTINCT: 去除重复，产生虚拟表VT9;

(10) ORDER BY: 将虚拟表VT9中的记录按照进行排序操作，产生虚拟表VT10;

(11) LIMIT: 取出指定街行的记录，产生虚拟表VT11，并返回给查询用户

SELECT

Persons.LastName,

Persons.FirstName,

Orders.OrderNo

FROM

Persons,

Orders

WHERE

Persons.Id_P = Orders.Id_P

SELECT

Persons.LastName,

Persons.FirstName,

Orders.OrderNo

FROM

Persons

INNER JOIN Orders ON

Persons.Id_P = Orders.Id_P

ORDER BY

Persons.LastName

除了我们在上面的例子中使用的 INNER JOIN(内连接)，我们还可以使用其他几种连接。

下面列出了您可以使用的 JOIN 类型，以及它们之间的差异。

JOIN: 如果表中有至少一个匹配，则返回行

INNER JOIN 与 JOIN 是相同的。

LEFT JOIN: 即使右表中没有匹配，也从左表返回所有的行

RIGHT JOIN: 即使左表中没有匹配，也从右表返回所有的行

FULL JOIN: 只要其中一个表中存在匹配，就返回行

UPDATE

表名

set

VALUES1 = 'xxx',

VALUE2 = 'xxxxx';

insert

into

表名(value1, value2)

values ('xx', 'xx')

---从某个表中查询数据，插入另外的表中

insert

into

table1(value1, 2)

select

VALUES1,

VALUES2

FROM

table2

--复制整个表

SELECT

*

INTO

OrdersBackup

FROM

Orders;

CREATE TABLE OrdersBackup AS

SELECT

*

FROM

Orders;

--where较select先执行，要使用select中的别名，解决方法是将含有别名列的查询放入内嵌视图，就可以在外层查询中引用别名列。内嵌视图的别名为 X

select

*

from

(

select

ID as i, goodsno as no_1

from

ALU_ss )x

where

i = '1';

select

prod_name,

prod_desc

from

products

where

prod_desc LIKE '%toy%'

and prod_desc LIKE '%carrots%';

select

prod_name,

prod_desc

from

products

where

prod_desc LIKE '%toy%carrots%';

select

vend_id,

vend_name as vname,

vend_address as vaddress,

vend_city as vcity

from

vendors

order by

vend_name;

select

prod_id,

prod_price,

prod_price*0.9 as sale_price

from

products;

--复制表数据，已经建好了表结构，该语句只能复制表的结构。该语句不会创建和复制源相同的主键、索引、约束和触发器。

INSERT

into

newtable

select

name,sex ---COLUMN

FROM

sourcetable;

--复制表和表结构。该语句不会创建和复制源相同的主键、索引、约束和触发器。

insert

into

newtables

from

sourcetables

where

whereexpression；

select

cust_id,

customer_name,

CONCAT(UPPER(LEFT(cust_contact, 2)), LEFT(cust_city, 3)))as user_login

from

customers;

select

order_num,

order_data

from

orders

where

year(order_data)= 2020

and month(order_data) = 1;

select

SUM(quantity)

from

orderitems;

select

SUM(quantity)

from

orderitems

where

prod_item = 'BR01';

select

MAX(prod_price) as max_price

from

products

where

prod_price < = 10;

select

order_num,

COUNT(*) as order_lines

from

orderitems

group by

order_num

order by

order_lines;

select

prod_id,

MIN(prod_price) as cheapest_item

from

products

group by

prod_id

order by

cheapest_item ;

SELECT

order_num

FROM

OrderItems

GROUP BY

order_num

HAVING

SUM(quantity) >= 100

ORDER BY

order_num;

SELECT

order_num

FROM

OrderItems

GROUP BY

order_num --group by 后只能放实际的列，而不是用于执行汇总计算的列。

HAVING

SUM(item_price * quantity) >= 1000

ORDER BY

order_num;

select

cust_id

from

orders

where

order_num IN (

select

order_num

from

orderitems

where

item_price > = 10)

select

cust_id,

cust_date

from

orders

where

order_num in (

select

ORDER_num

from

orderitem

where

prod_id = 'BR01')

order by

cust_date;

select

cust_email

from

customers

where

cust_id in (

select

cust_id,

from

orders

where

order_num in (

select

ORDER_num

from

orderitem

where

prod_id = 'BR01') );

----订单表、顾客表、项目表 in = exists

select

cust_id,

(

select

SUM(item_price*quantity)

from

orderitems

where

orderitems.order_num = orders.orders_num) as total_ordered

from

orders

order by

total_ordered desc;

select

cust_id,

SUM(i.item_price*i.quantity) as total_ordered

from

orders o

join orderitems i on

i.order_num = o.orders_num

order by

total_ordered desc;

select

prod_name,

(

select

SUM(quantity)

from

orderitems

where

products.prod_id = orderitems.prod_id) as quant_sold

from

products;

select

cust_name,

orders_num

from

customers c

join orders o on

o.cust_id = c.cust_id

order by

cust_name,

orders_num

SELECT

cust_name,

order_num,

(

SELECT

Sum(item_price*quantity)

FROM

OrderItems

WHERE

Orders.order_num = OrderItems.order_num) AS OrderTotal

FROM

Customers,

Orders

WHERE

Customers.cust_id = Orders.cust_id

ORDER BY

cust_name,

order_num;

select

cust_name,

orders_num,

SUM(item_prices*quantity) as orderTotal

from

orders o

join customers c on

o.cust_id = c.cust_id

join orderitem i on

o.order_num = i.order_num

order by

cust_name,

orders_num

SELECT

cust_email

FROM

Customers

INNER JOIN Orders ON

Customers.cust_id = Orders.cust_id

INNER JOIN OrderItems ON

Orders.order_num = OrderItems.order_num

WHERE

prod_id = 'BR01';

select --6

cust_name,

SUM(item_prices*quanirty) as total_price

from --1

orders

join orderitems on

orderitems.order_num = orders.order_num

join customers on---3

orders.cust_id = customers.cust_id --2

GROUP BY --4

cust_name

HAVING --5

SUM(item_prices*quanirty) >=1000

order BY --7

cust_name

select

cust_name,

order_num

from

customers

join orders on

orders.cust_id = custmers.cust_id;

select

cust_name,

order_num

from

customers

left outer join orders on

orders.cust_id = custmers.cust_id;

select

prod_name,

order_num

from

products

left outer join orderitems on

orderitems.prod_id = products.prod_id

order by

prod_name

select

vendors.vend_id,

COUNT(prod_id)

from

vendors

left outer join products on

products.vend_id = vendors.vend_id

group by

vendors.vend_id;

select

prod_id,

quantity

from

orderitems

where

quantity = 1000

union

select

prod_id,

quantity

from

orderitems

where

proid_id like 'BNBG%'

order by

prod_id

select

prod_id,

quantity

from

orderitems

where

quantity = 1000

or proid_id like 'BNBG%'

order by

prod_id;

INSERT

into

customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_email)

values(1000000042, 'Ben''s Toys', '123 Main Street', 'Oak Park', 'MI', '48237', 'USA', 'ben@forta.com');

update

vendors

set

UPPER(vend_state)

where

vend_country = 'USA'

UPDATE

customers

set

cust_state = UPPER(cust_state)

where

cust_country = 'USA'

alter TABLE vendors add vend_web char(100)

create view customerswithorders as

select

Customers.cust_id,

Customers.cust_name,

Customers.cust_address,

Customers.cust_city,

Customers.cust_state,

Customers.cust_zip,

Customers.cust_country,

Customers.cust_contact,

Customers.cust_email

from

customers

join orders on

orders.cust_id = custers.id;

--同时使用内置函数 NEWID 和 TOP、ORDER BY 来返回一个随机结果集。

select

TOP 5 *

from

zd_MAData_erp

order by

newid();

--MY SQL把内置函数 RAND 和 LIMIT、ORDER BY 结合使用 来返回一个随机结果集。

select

ename,

job

from

zd_MAData_erp

order by

rand()

limit 5

select id,

case

when MAName is not null then MAName

else '空'

end

from

zd_MAData_erp;

select

mc,

coalesce(cfdd, '空')

from

ERP_BXG_YCL_Inventoryclass;

select

ename,

sal,

case

when sal <= 2000 then 'UNDERPAID'

when sal >= 4000 then 'OVERPAID'

else 'OK'

end as status

from

emp

select

bm ,

mc ,

gys

from

ERP_BXG_YCL_Inventoryclass

order by

2;

select

bm ,

mc ,

gys

from

ERP_BXG_YCL_Inventoryclass

order by

SUBSTRING(mc,LEN(mc)-2,2)

select

CONCAT(bm , mc ) as data1

from

ERP_BXG_YCL_Inventoryclass;