8.7.3. Type Safety

8.7.3. Type Safety

8.7.3.类型安全

Each enumerated data type is separate and cannot be compared with other enumerated types. See this example:

每个枚举类型是独立的，且不能与其他枚举类型比较。例如：

 

CREATE TYPE happiness AS ENUM ('happy', 'very happy', 'ecstatic');

CREATE TABLE holidays (

num_weeks integer,

happiness happiness

);

INSERT INTO holidays(num_weeks,happiness) VALUES (4, 'happy');

INSERT INTO holidays(num_weeks,happiness) VALUES (6, 'very happy');

INSERT INTO holidays(num_weeks,happiness) VALUES (8, 'ecstatic');

INSERT INTO holidays(num_weeks,happiness) VALUES (2, 'sad');

ERROR: invalid input value for enum happiness: "sad"

SELECT person.name, holidays.num_weeks FROM person, holidays

WHERE person.current_mood = holidays.happiness;

ERROR: operator does not exist: mood = happiness

 

If you really need to do something like that, you can either write a custom operator or add explicit casts to your query:

如果确实想要这样做，那么可以写一个自定义的操作符，或者在查询中进行显式的类型转换：

 

SELECT person.name, holidays.num_weeks FROM person, holidays

WHERE person.current_mood::text = holidays.happiness::text;

name | num_weeks

------+-----------

Moe | 4

(1 row)