用连接更新表？

Question

我试图用表B中的数据更新表A.我想我可以做这样的事情

update A 
set A.DISCOUNT = 3 
from INVOICE_ITEMS A
join ITEM_PRICE_QUNTITY B on A.ITEM_PRICE_NO = B.ID
where A.INVOICE_ID = 33

但收到错误SQL消息:-104无效的令牌

谁能帮我？

Answer 1

这是不可能的JOIN.Firebird UPDATE声明没有任何FROM条款.该语法是:

UPDATE {tablename | viewname} [[AS] alias]
   SET col = newval [, col = newval ...]
   [WHERE {search-conditions | CURRENT OF cursorname}]
   [PLAN plan_items]
   [ORDER BY sort_items]
   [ROWS <m> [TO <n>]]
   [RETURNING <values>]

<m>, <n>     ::=  Any expression evaluating to an integer.
<values>     ::=  value_expression [, value_expression ...]
<variables>  ::=  :varname [, :varname ...]

但是,您的示例查询的等价物是:

update INVOICE_ITEMS 
set DISCOUNT = 3 
WHERE EXISTS (SELECT 1 FROM ITEM_PRICE_QUNTITY B WHERE B.ID = ITEM_PRICE_NO)
AND INVOICE_ID = 33

如果要使用其他表中的数据进行更新,可能需要考虑使用MERGE.在您的评论中,您要求使用等效查询与Firebird执行以下操作:

UPDATE B 
SET B.QUANTIY = b.QUANTIY + a.QUANTITY 
FROM ITEM_PRICE_QUNTITY B JOIN INVOICE_ITEMS A ON A.ITEM_PRICE_NO = B.ID 
WHERE A.INVOICE_ID = 33

等同的MERGE陈述是:

MERGE INTO ITEM_PRICE_QUNTITY AS B
    USING INVOICE_ITEMS AS A
    ON A.ITEM_PRICE_NO = B.ID AND A.INVOICE_ID = 33
    WHEN MATCHED THEN
        UPDATE SET B.QUANTIY = B.QUANTIY + A.QUANTITY 

Answer 2

从FB手册来看，如果您使用的是Firebird 2.0或以上版本，您可以使用EXECUTE BLOCK编写更有效的语句：

EXECUTE BLOCK
AS
DECLARE VARIABLE field1 type;
DECLARE VARIABLE field2 type;
-- ...etc.
DECLARE VARIABLE pk type;
BEGIN
   for select pk, field1, field2, ... from src_table
   into :pk, :field1, :field2, ...
   do update dest_table set field1 = :field1, field2 = :field2, -- ...
   where pk = :pk;
END