PostgreSQL创建一个新列，其值以其他列为条件 [英] PostgreSQL create a new column with values conditioned on other columns

问题描述

我使用PostgreSQL 9.1.2，我有一个基本表，如下所示，其中我具有布尔值（Survival）的条目的生存状态，以及数量的天数（生存（天数））。

I use PostgreSQL 9.1.2 and I have a basic table as below, where I have the Survival status of an entry as a boolean (Survival) and also in number of days (Survival(Days)).

我手动添加了一个名为 1-yr Survival 的新列，现在我想填写表格中每个条目的此列，取决于该条目的 Survival 和 Survival（Days）列值。一次，完成后，数据库表将如下所示：

I have manually added a new column named 1-yr Survival and now I want to fill in the values of this column for each entry in the table, conditioned on that entry's Survival and Survival (Days) column values. Once , completed the database table would look something like this:

Survival    Survival(Days)    1-yr Survival
----------  --------------    -------------
Dead            200                NO
Alive            -                 YES
Dead            1200               YES

用于输入 1-yr生存类似于：

ALTER TABLE mytable ADD COLUMN "1-yr Survival" text
for each row
if ("Survival" = Dead & "Survival(Days)" < 365) then Update "1-yr Survival" = NO
else Update "1-yr Survival" = YES
end 

我相信这是一项基本操作，但是我无法找到要执行的postgresql语法。一些搜索结果返回添加触发器，但是我不确定这是我所需要的。我认为我的情况要简单得多。任何帮助/建议将不胜感激。

I believe this is a basic operation however I failed to find the postgresql syntax to execute it. Some search results return "adding a trigger", but I am not sure that is what I neeed. I think my situation here is a lot simpler. Any help/advice would be greatly appreciated.

推荐答案

一次性操作只需使用 UPDATE ：

UPDATE tbl
SET    one_year_survival = (survival OR survival_days >= 365);

我建议不要在名称中使用驼峰式，空格和括号。尽管允许在双引号之间，但它经常导致复杂和混乱。考虑有关手册中标识符和关键字的一章。

I would advise not to use camel-case, white-space and parenthesis in your names. While allowed between double-quotes, it often leads to complications and confusion. Consider the chapter about identifiers and key words in the manual.

您知道您可以使用CSV了。 postgresql.org/docs/current/interactive/sql-copy.html> COPY ？

示例：

Are you aware that you can export the results of a query as CSV with COPY?
Example:

COPY (SELECT *, (survival OR survival_days >= 365) AS one_year_survival FROM tbl)
TO '/path/to/file.csv';

开始时，您不需要冗余列。

You wouldn't need the redundant column this way to begin with.

为避免出现空更新：

UPDATE tbl
SET    "Dead after 1-yr" = (dead AND my_survival_col < 365)
      ,"Dead after 2-yrs" = (dead AND my_survival_col < 730)
....
WHERE  "Dead after 1-yr" IS DISTINCT FROM (dead AND my_survival_col < 365)
   OR  "Dead after 2-yrs" IS DISTINCT FROM (dead AND my_survival_col < 730)
...

就我个人而言，如果我有令人信服的理由，我只会添加这样的冗余列。通常我不会。如果是关于性能：您是否了解关于表达式和部分索引的索引？

Personally, I would only add such redundant columns if I had a compelling reason. Normally I wouldn't. If it's about performance: are you aware of indexes on expressions and partial indexes?

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