基本上,我想这样做:
update vehicles_vehicle v
join shipments_shipment s on v.shipment_id=s.id
set v.price=s.price_per_vehicle;
我很确定这在MySQL(我的背景)中可以工作,但在postgres中似乎不起作用。我得到的错误是:
ERROR: syntax error at or near "join"
LINE 1: update vehicles_vehicle v join shipments_shipment s on v.shi...
^
当然有一个简单的方法来做到这一点,但我找不到合适的语法。那么,我该如何在PostgreSQL中写这个呢?
UPDATE语法为:
[ WITH [ RECURSIVE ] with_query [, ...] ]
UPDATE [ ONLY ] table [ [ AS ] alias ]
SET { column = { expression | DEFAULT } |
( column [, ...] ) = ( { expression | DEFAULT } [, ...] ) } [, ...]
[ FROM from_list ]
[ WHERE condition | WHERE CURRENT OF cursor_name ]
[ RETURNING * | output_expression [ [ AS ] output_name ] [, ...] ]
在你的情况下,我认为你想要的是:
UPDATE vehicles_vehicle AS v
SET price = s.price_per_vehicle
FROM shipments_shipment AS s
WHERE v.shipment_id = s.id
或者如果你需要连接两个或多个表:
UPDATE table_1 t1
SET foo = 'new_value'
FROM table_2 t2
JOIN table_3 t3 ON t3.id = t2.t3_id
WHERE
t2.id = t1.t2_id
AND t3.bar = True;
我举个例子再解释一下。
任务:正确的信息,在哪里abiturients(即将离开中学的学生)提交申请大学早于他们获得学校证书(是的,他们获得证书早于他们颁发的证书(指定证书日期)。因此,我们将增加申请提交日期,以适应证书颁发日期。
因此。下一个mysql类语句:
UPDATE applications a
JOIN (
SELECT ap.id, ab.certificate_issued_at
FROM abiturients ab
JOIN applications ap
ON ab.id = ap.abiturient_id
WHERE ap.documents_taken_at::date < ab.certificate_issued_at
) b
ON a.id = b.id
SET a.documents_taken_at = b.certificate_issued_at;
以这样的方式变得像postgresql
UPDATE applications a
SET documents_taken_at = b.certificate_issued_at -- we can reference joined table here
FROM abiturients b -- joined table
WHERE
a.abiturient_id = b.id AND -- JOIN ON clause
a.documents_taken_at::date < b.certificate_issued_at -- Subquery WHERE
可以看到,原来的子查询JOIN的ON子句已经变成了WHERE条件之一,由AND与其他子查询连接,这些子查询已经从子查询中移动,没有任何变化。并且不再需要将表与自身连接(就像在子查询中那样)。
在这种情况下,Mark Byers的答案是最优的。
尽管在更复杂的情况下,你可以使用select查询返回rowids和计算值,并将其附加到更新查询,如下所示:
with t as (
-- Any generic query which returns rowid and corresponding calculated values
select t1.id as rowid, f(t2, t2) as calculatedvalue
from table1 as t1
join table2 as t2 on t2.referenceid = t1.id
)
update table1
set value = t.calculatedvalue
from t
where id = t.rowid
这种方法允许您开发和测试选择查询,并在两个步骤中将其转换为更新查询。
所以在你的例子中,结果查询将是:
with t as (
select v.id as rowid, s.price_per_vehicle as calculatedvalue
from vehicles_vehicle v
join shipments_shipment s on v.shipment_id = s.id
)
update vehicles_vehicle
set price = t.calculatedvalue
from t
where id = t.rowid
请注意,列别名是必须的,否则PostgreSQL将抱怨列名的模糊性。
在上面所有的答案中添加一些非常重要的东西,当你想要更新连接表时,你可能会遇到两个问题:
您不能使用您想要更新的表来JOIN另一个表
Postgres希望在JOIN之后有一个ON子句,因此不能只使用where子句。
这意味着基本上,以下查询是无效的:
UPDATE join_a_b
SET count = 10
FROM a
JOIN b on b.id = join_a_b.b_id -- Not valid since join_a_b is used here
WHERE a.id = join_a_b.a_id
AND a.name = 'A'
AND b.name = 'B'
UPDATE join_a_b
SET count = 10
FROM a
JOIN b -- Not valid since there is no ON clause
WHERE a.id = join_a_b.a_id
AND b.id = join_a_b.b_id
a.name = 'A'
AND b.name = 'B'
相反,你必须像这样使用FROM子句中的所有表:
UPDATE join_a_b
SET count = 10
FROM a, b
WHERE a.id = join_a_b.a_id
AND b.id = join_a_b.b_id
AND a.name = 'A'
AND b.name = 'B'
这对一些人来说可能很简单,但我被这个问题困住了,想知道发生了什么,所以希望它能帮助到其他人。
在PostGRE SQL / AWS (SQL工作台)中使用另一个表更新一个表。
在PostGRE SQL中,你需要在UPDATE Query中使用join:
UPDATE TABLEA set COLUMN_FROM_TABLEA = COLUMN_FROM_TABLEB FROM TABLEA,TABLEB WHERE FILTER_FROM_TABLEA = FILTER_FROM_TABLEB;
Example:
Update Employees Set Date_Of_Exit = Exit_Date_Recorded , Exit_Flg = 1 From Employees, Employee_Exit_Clearance Where Emp_ID = Exit_Emp_ID
表A - Employees列表A - Date_Of_Exit,Emp_ID,Exit_Flg表B是- Employee_Exit_Clearance列表B - Exit_Date_Recorded,Exit_Emp_ID
1760行受影响
执行时间:29.18秒
第一种方式比第二种方式慢。
第一:
DO $$
DECLARE
page int := 10000;
min_id bigint; max_id bigint;
BEGIN
SELECT max(id),min(id) INTO max_id,min_id FROM opportunities;
FOR j IN min_id..max_id BY page LOOP
UPDATE opportunities SET sec_type = 'Unsec'
FROM opportunities AS opp
INNER JOIN accounts AS acc
ON opp.account_id = acc.id
WHERE acc.borrower = true
AND opp.sec_type IS NULL
AND opp.id >= j AND opp.id < j+page;
COMMIT;
END LOOP;
END; $$;
第二:
DO $$
DECLARE
page int := 10000;
min_id bigint; max_id bigint;
BEGIN
SELECT max(id),min(id) INTO max_id,min_id FROM opportunities;
FOR j IN min_id..max_id BY page LOOP
UPDATE opportunities AS opp
SET sec_type = 'Unsec'
FROM accounts AS acc
WHERE opp.account_id = acc.id
AND opp.sec_type IS NULL
AND acc.borrower = true
AND opp.id >= j AND opp.id < j+page;
COMMIT;
END LOOP;
END; $$;