Question

我通过连接使用两个表进行选择。我需要使用第二个表字段更新第一个表。选择如下

ActiveRecord::Schema.define(version: 20150709110928) do

create_table "author_books", id: false, force: :cascade do |t|
  t.integer  "author_id"
  t.integer  "book_id"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

add_index "author_books", ["author_id"], name:  
          "index_author_books_on_author_id"
add_index "author_books", ["book_id"],    
           name:"index_author_books_on_book_id"

create_table "authors", force: :cascade do |t|
  t.string   "name"
  t.string   "surname"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

create_table "books", force: :cascade do |t|
  t.string   "title"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

end

我如何更新对应于Table1的相同选择（SET R.f2 = Z.f2）？

select R.f1, Z.f2,R.f3 
FROM
(select * From Table1 where f2<>'xx' and f3='z') R inner join
(select * From Table2 where f3='xx')             Z 
 ON R.f1⁼Z.f1 and R.f4=Z.f4

当我尝试时，我收到了回复

UPDATE的目标表R不可更新

Answer 1

您可以使用以下内容在update语句中使用联接....

update t
   set t.Column = value
  from Table t
 inner join OtherTable ot on t.Id = ot.TID
 where somecondition = true.

Answer 2

您应该在table1上执行更新并将其加入第二个子查询。第一个子查询中table1的条件可以应用于where子句：

UPDATE table1 r
JOIN   (SELECT * FROM table2 WHERE f3 = 'xx') z  ON r.f1 ⁼ z.f1 AND r.f4 = z.f4
SET    r.f2 = z.f2
WHERE  r.f2 <> 'xx' AND r.f3 = 'z'

使用join更新单个表

2 个答案: