基于具有值替换的两个表创建视图

Question

我遇到了一个查询，但我不确定该怎么做。

我想创建一个视图 my_view 基于 table original_data_table 其中每个值都由 table [=56 中的非空值替换=] 只要指定了 id。

original_data_table和replacement_data_table 具有相同的结构，但具有不同的值。

我尝试在我的查询中使用 JOIN，但我不确定它是否可行。

SELECT * FROM original_data_table AS o
LEFT JOIN replacement_data_table AS r
ON o.id = r.id

original_data_table

id         name        value

1          David       10
2          John        20
3          Sarah       30
4          Amy         40

replacement_data_table

id         name        value

1          NULL        50
2          Rick        NULL
4          Emma        60

my_view

id         name        value

1          David       50
2          Rick        20
3          Sarah       30
4          Emma        60

Answer 1

你需要COALESCE()从右边得到正确的值table:

SELECT o.id,
       COALESCE(r.name, o.name) as name,
       COALESCE(r.value, o.value) as value
FROM original_data_table o LEFT JOIN
     replacement_data_table r
     ON o.id = r.id;

Answer 2

试试这个：

SELECT o.id as id, IFNULL(r.name, o.name) as new_name, IFNULL(r.value, o.value) as new_value
FROM original_data_table AS o
LEFT JOIN replacement_data_table AS r
ON o.id = r.id

Answer 3

尝试使用 case when

SELECT 
  o.`id`,case when o.`name` <> r.`name` and r.`name` is not null then
      r.`name`
    else o.`name`
  end as name
  ,case when o.`value` <> r.`value` and r.`value` is not null then
      r.`value`
    else o.`value`
  end as value
FROM original_data_table AS o
LEFT JOIN replacement_data_table AS r
  ON o.id = r.id 
order by o.id

SQL Fiddle Demo Link

| id |  name | name |
|----|-------|------|
|  1 | David |   50 |
|  2 |  Rick |   20 |
|  3 | Sarah |   30 |
|  4 |  Emma |   60 |

基于具有值替换的两个表创建视图

Create a view based on two tables with value substitution

mysql

sql

replace

substitution