如果 id 存在于另一个表中，则有条件地插入到另一个表中，否则插入到 oracle 中的两个表中

Question

如果表A 中存在客户 ID，则在表 B中插入订单。 如果A 表中没有客户 ID，则在 A表中插入客户 ID，然后在B表中订购。 我一直在尝试通过if/else 和 merge来实现这一点，但一直遇到无效的 sql 语句。

IF EXISTS (SELECT CustomerID FROM Customer_T WHERE CustomerID = 18)
    Insert into Order_T
    values(79,18,to_date('09/28/2021','mm/dd/yyyy'),to_date('10/01/2021','mm/dd/yyyy'),1,3)
ELSE
  insert INTO Customer_T VALUES (18,'Capitol Industries Ltd', '999 Fifth Avenue', 'New York', 'NY','10015')
  insert into Order_T values (79,18,to_date('09/28/2021','mm/dd/yyyy'),to_date('10/01/2021','mm/dd/yyyy'),1,3)
END IF;

Answer 1

这种情况不需要IF THEN ELSE逻辑。 而是使用数据库内置功能。 customerid 应该是您的主键，因此如果您尝试插入并且它已经存在，则会引发DUP_VAL_ON_INDEX异常。

检查以下示例：

-- create tables
create table customers (
    id                             number generated by default on null as identity 
                                   constraint customers_id_pk primary key,
    name                           varchar2(255 char)
)
;

create table orders (
    id                             number generated by default on null as identity 
                                   constraint orders_id_pk primary key,
    customer_id                    number
                                   constraint orders_customer_id_fk
                                   references customers on delete cascade,
    product                        varchar2(100 char)
)
;

BEGIN
  BEGIN
    insert INTO customers VALUES (2,'Capitol Industries Ltd');
  EXCEPTION WHEN DUP_VAL_ON_INDEX THEN
    NULL; 
  END;
  insert into orders (customer_id,product) values (2,'a book');
END;  
/

运行上面的块几次。 只有第一次它会插入一个客户。

Answer 2

假设您有 2 个非常简单的表。

表

create table T1( num_ )
as
select 1 from dual ;

create table T2( num_ )
as
select 200 from dual ;

包含 IF.. ELSE.. END IF 和 EXISTS() 的匿名块类似于您问题中的代码，会导致错误：

function 或伪列“EXISTS”只能在 SQL 语句中使用

    begin
      if exists( select num_ from T1 where num_  = 2 ) then
        insert into T2( num_ ) values( 2 ) ;
        dbms_output.put_line( 'if' ) ;
      else
        insert into T1( num_ ) values( 2 ) ;
        insert into T2( num_ ) values( 2 ) ;
        dbms_output.put_line( 'else' ) ;
      end if ;
    end ;
    /
-- error:
... function or pseudo-column 'EXISTS' may be used inside a SQL statement only

一种解决方案可能是执行以下操作（请参阅 asktom.oracle.com - 相当于 IF 语句中的 EXISTS() ）

begin
  for x in ( select count(*) cnt
             from dual
             where exists ( select num_ from T1 where num_  = 2  ) 
  ) loop
    if ( x.cnt = 1 ) then                  -- found
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'if' ) ;
    else                                   -- not found
      insert into T1( num_ ) values( 2 ) ;
      insert into T2( num_ ) values( 2 ) ;
      dbms_output.put_line( 'else' ) ; 
    end if;
  end loop;
end;
/

-- output:
1 rows affected

dbms_output:
else  

第一次执行匿名块后，表中包含以下行：

select num_, '<- T1' as table_ from T1
union all
select num_, '<- T2' from T2 ;

-- result
NUM_    TABLE_
1       <- T1
2       <- T1
200     <- T2
2       <- T2

再次执行匿名块，你会得到...

1 rows affected

dbms_output:
if

-- tables
NUM_    TABLE_
1       <- T1
2       <- T1
200     <- T2
2       <- T2
2       <- T2

DBfiddle 在这里。

Answer 3

您可以使用多表插入并使用这样一个事实，即没有group by聚合 function 在不存在（= 不满足where条件）行的情况下总是返回带有null的行。

代码如下：

 insert into customers(id, name, company, state) values (1, 'Some name', 'Some company', 'NY')

1 行受影响

insert all when cust_exists = 0 then into customers (id, name, company, state) values (cust_id, cust_name, company, state) when 1 = 1 then into orders (id, customer_id, order_date, due_date, some_id) values(order_id, cust_id, order_date, due_date, some_id) select 1 as order_id, 1 as cust_id, 'Some other name' as cust_name, 'Company' as company, 'NY' as state, date '2021-09-28' as order_date, date '2021-10-03' as due_date, 100 as some_id, nvl(max(1), 0) as cust_exists from customers where id = 1

1 行受影响

insert all when cust_exists = 0 then into customers (id, name, company, state) values (cust_id, cust_name, company, state) when 1 = 1 then into orders (id, customer_id, order_date, due_date, some_id) values(order_id, cust_id, order_date, due_date, some_id) select 2 as order_id, 2 as cust_id, 'Some other name' as cust_name, 'Company' as company, 'NY' as state, date '2021-09-28' as order_date, date '2021-10-03' as due_date, 100 as some_id, nvl(max(1), 0) as cust_exists from customers where id = 2

2 行受影响

您还可以使用两个带有记录ignore_row_on_dupkey_index提示的插入，这正如其名称所暗示的那样。

 insert /*+ ignore_row_on_dupkey_index(customers(id)) */ into customers (id, name, company, state) values (2, 'Name', 'Comp', 'NY')

✓

 insert into orders (id, customer_id, order_date, due_date, some_id) values (3, 2, date '2021-09-30', date '2021-10-07', 5)

1 行受影响

select * from customers

ID	姓名	公司	STATE
1个	一些名字	某公司	纽约
2个	其他名字	公司	纽约

db<> 在这里摆弄