sql 中 exists 关键字的用法

好久没发表博客了，今日偶有闲暇仔细研究了一遍oracle中exists 的用法,整理了在一起，记录在itieye,以防后忘。。。。嘎嘎

1. 关于数据首先做好数据的初始化工作

-- Create table
create table CUSTOMERS
(
CID NUMBER not null,
CNAME VARCHAR2(50) not null
)
alter table CUSTOMERS
add constraint CUSTOMERS_PK primary key (CID)
using index
tablespace USERS

-- Create sequence

create sequence SEQ_CUSTOMERS
minvalue 1
maxvalue 999999
start with 1
increment by 1
cache 20;

select * from customers;

insert into customers values(seq_customers.nextval,'张三');

insert into customers values(seq_customers.nextval,'李四');
insert into customers values(seq_customers.nextval,'王五');

--------------------------------------------------------------------------
-- Create table
create table ORDERS
(
OID   NUMBER not null,
ONAME VARCHAR2(50) not null,
CID   NUMBER
)
-- Create/Recreate primary, unique and foreign key constraints
alter table ORDERS
add constraint ORDERS_PK primary key (OID)
using index
tablespace USERS
pctfree 10
initrans 2
maxtrans 255
storage
(
    initial 64K
    minextents 1
    maxextents unlimited
);

-- Create sequence
create sequence SEQ_ORDERS
minvalue 1
maxvalue 999999
start with 1
increment by 1
cache 20;

insert into orders values(seq_orders.nextval,'订单1','1');
insert into orders values(seq_orders.nextval,'订单2','2');
insert into orders values(seq_orders.nextval,'订单3','2');

/* 查询图书的标题，这些图书是有出版商的，换句话查询的是有出版商的图书的图书标题*/

1.使用exists 关键字

select title from books where exists (select 1 from publishers where pub_id = books.pub_id);

2. 使用in

select * from books where pub_id in (select pub_id from publishers);

----------------------------------------------------------------------

not exists 和exists

/* 查询没有出版过书的出版商的名称 */
select name from publishers where not exists ( select 1 from books where pub_id = publishers.pub_id)

查询这些出版商的名称是在图书表中没有对应的记录这些出版商的id

/* 查询有出版过书的出版商的名称 */
select name from publishers where exists ( select 1 from books where pub_id = publishers.pub_id)

sql 中 exists 关键字的用法

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