如何不对 PostgreSQL CASE 表达式的 ELSE 部分求值

Question

I have to convert two types of input to a valid timestamp:

1. '1626273917256'
2. '2021-07-14 16:45:17+02'

Right now I'm doing it like this:

timestamp_comumn = CASE WHEN ? ~ '\d{13}' THEN to_timestamp(?::bigint/1000) ELSE ?::timestamp END

For the case when the input is '1626273917256', this results in:

timestamp_comumn = CASE WHEN '1626273917256' ~ '\d{13}' THEN to_timestamp('1626273917256'::bigint/1000) ELSE '1626273917256'::timestamp END

But this throws an error:

SELECT CASE WHEN '1626273917256' ~ '\d{13}' THEN to_timestamp('1626273917256'::bigint/1000) ELSE '1626273917256'::timestamp END

ERROR:  date/time field value out of range: "1626273917256"
LINE 1: ...N to_timestamp('1626273917256'::bigint/1000) ELSE '162627391...
                                                             ^
HINT:  Perhaps you need a different "datestyle" setting.

clearly because PostgreSQL evaluates the ELSE part as well.

Is there a way to do this in SQL? Or the only option is to do this in the scripting part?

Answer 1

Your tests are deceiving you as to how this will work in production.

PostgreSQL can see that '1626273917256'::timestamp is a constant and tries to evaluate it ahead of time. As long as you are referencing something other than a literal you should be fine.

=> WITH str_times (t) AS (VALUES ('1626273917256'::text)) SELECT CASE WHEN t ~ '\d{13}' THEN to_timestamp(t::bigint/1000) ELSE t::timestamp END FROM str_times;
           t            
────────────────────────
 2021-07-14 14:45:17+00
(1 row)