如何更新 postgres 表列并将值设置为和枚举类型

Question

Say I have a table with two columns

first is called "temp_status", which is an int with values, 0,1,2,3,4 and the other is called "status" which is of type enum, with values, "Enum1", "Enum2", "Enum3", "Enum4", "Enum5",

I want to assign values to the "status" column based on "temp_status" column. I did the following and got the following error:

UPDATE "Table"
SET "status" =
CASE
    WHEN "temp_status" = 0 THEN 'Enum1'
    WHEN "temp_status" = 1 THEN 'Enum2'
    WHEN "temp_status" = 2 THEN 'Enum3'
    WHEN "temp_status" = 3 THEN 'Enum4'
    WHEN "temp_status" = 4 THEN 'Enum5'
    ELSE 'Enum1'  -- default value
END
WHERE "temp_status" IN (0, 1, 2, 3, 4);

I got this error;

ERROR: column "status" is of type "MyEnumName" but expression is of type text
HINT: You will need to rewrite or cast the expression.

The enum values match so I am wondering how I need to do the casting here

Answer 1

You're just missing a cast to the enum strings, eg

UPDATE t
SET status =
  CASE
    WHEN temp_status = 0 THEN 'Enum1'::MyEnumName
    WHEN temp_status = 1 THEN 'Enum2'::MyEnumName
    WHEN temp_status = 2 THEN 'Enum3'::MyEnumName
    WHEN temp_status = 3 THEN 'Enum4'::MyEnumName
    WHEN temp_status = 4 THEN 'Enum5'::MyEnumName
    ELSE 'Enum1'  -- default value
  END
WHERE temp_status IN (0, 1, 2, 3, 4);

Note: the default value will never be reached, as the values of temp_status are constraint to values that are already mapped in the case conditions (0, 1, 2, 3, 4).

However, since your enums can be easily mapped to the column temp_status , you can substantially simplify the update by concatenating 'Enum' and the content of temp_status :

UPDATE t 
SET status = ('Enum'||temp_status+1)::MyEnumName
WHERE "temp_status" IN (0, 1, 2, 3, 4);

Demo: db<>fiddle