生成列中连接字符串的 NULL 输入

Question

我有一张桌子

CREATE TABLE IF NOT EXISTS club.climbers (
    climber_id SERIAL PRIMARY KEY,
    climber_first_name VARCHAR(20) NOT NULL,
    climber_last_name VARCHAR(30) NOT NULL,
    climber_full_name TEXT GENERATED ALWAYS AS (climber_first_name || ' ' || climber_last_name) STORED NOT NULL,
    sex_id INTEGER NOT NULL REFERENCES club.sex,
    climber_date_birth DATE NOT NULL,
    climber_phone VARCHAR(20) NOT NULL,
    postal_code_id INTEGER REFERENCES club.postal_codes,
    street VARCHAR(75) NOT NULL,
    building VARCHAR(5) NOT NULL,
    apartment VARCHAR(5),
    full_address TEXT GENERATED ALWAYS AS (street || ',' || building || '-' || apartment) STORED
);

但是

apartment

可以为 NULL，然后

full_address

也将为 NULL。我需要忽略

apartment

中的 NULL 值。

我尝试使用

CONCAT

和

COALESCE

，但我不知道当

apartment

为 NULL 时如何抑制悬空的“-”。

Answer 1

您可以将

-

包含在 coalesce() 的第一个参数中，例如：

full_address TEXT GENERATED ALWAYS AS (street || ',' || building || 
    coalesce('-' || apartment, '')) STORED);

Answer 2

一种选择是使用

CASE

表达式：

full_address TEXT GENERATED ALWAYS AS 
    (street || ',' || case when apartment is not null then building || '-' || apartment 
                           else building end) STORED

which - 用于插入为

insert into climbers (street, building, apartment) values ('Wall street', 'A', '10');
insert into climbers (street, building, apartment) values ('5th Avenue', 'B', null);

结果

street          building    apartment   full_address
Wall street     A           10          Wall street,A-10
5th Avenue      B           null        5th Avenue,B

参见小提琴。

Answer 3

你可以尝试这个解决方案，我没有任何例子来全面检查，但我相信它会起作用。

CREATE TABLE IF NOT EXISTS club.climbers
(
    climber_id SERIAL PRIMARY KEY,
    climber_first_name VARCHAR(20) NOT NULL,
    climber_last_name VARCHAR(30) NOT NULL,
    climber_full_name TEXT GENERATED ALWAYS AS (climber_first_name || ' ' || climber_last_name) STORED NOT NULL,
    sex_id INTEGER NOT NULL REFERENCES club.sex,
    climber_date_birth DATE NOT NULL,
    climber_phone VARCHAR(20) NOT NULL,
    postal_code_id INTEGER REFERENCES club.postal_codes,
    street VARCHAR(75) NOT NULL,
    building VARCHAR(5) NOT NULL,
    apartment VARCHAR(5),
    full_address TEXT GENERATED ALWAYS AS (
        street || ',' || building ||
        CASE WHEN apartment IS NOT NULL THEN '-' || apartment ELSE '' END
    ) STORED NOT NULL
);

Answer 4

您可以使用

concat

或

concat_ws

函数，它会忽略空值。

full_address TEXT GENERATED ALWAYS AS (concat(street, ',', building, '-', apartment)) STORED

Answer 5

理想情况：

immutable_concat_ws(' - ', street || ', ' || building, apartment)

其中

immutable_concat_ws()

是自定义函数，如下所述。

带有空格和分隔符的最佳表达式是：

concat_ws(' - ', street || ', ' || building, apartment)

参见：

• 如何在 Postgres SELECT 中连接列？

但是生成的列需要

IMMUTABLE

表达式。参见：

• PostgreSQL 中的计算/计算/虚拟/派生/生成列

因此，仅为文本输入创建自定义

immutable_concat_ws()

（这在您的情况下是有保证的）。理想情况下，作为超级用户：

CREATE OR REPLACE FUNCTION immutable_concat_ws(text, VARIADIC text[])
  RETURNS text
  LANGUAGE internal IMMUTABLE PARALLEL SAFE AS
'text_concat_ws';

参见：

• 创建 concat_ws 的不可变克隆

或者，没有超级用户权限，并且作为“标准 SQL”函数（需要 Postgres 14+）。参见：

• 如何在 Postgres SELECT 中连接列？

CREATE OR REPLACE FUNCTION immutable_concat_ws(text, VARIADIC text[])
  RETURNS text
  LANGUAGE sql IMMUTABLE PARALLEL SAFE
RETURN array_to_string($2, $1);