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Proposal: is_castable - Mailing list pgsql-hackers

From	Michał Wadas
Subject	Proposal: is_castable
Date	April 3, 2020 14:45:31
Msg-id	CAMEnU0Ae+h5zFoEra004NXTaPxPYABv4B9SdR9Tm15mNPT6OOQ@mail.gmail.com Whole thread Raw
Responses	Re: Proposal: is_castable (Pavel Stehule <pavel.stehule@gmail.com>) Re: Proposal: is_castable (Tom Lane <tgl@sss.pgh.pa.us>)
List	pgsql-hackers

Currently there is no way to check if CAST will succeed.

Therefore I propose adding new function: is_castable

SELECT is_castable('foo' as time) // false

SELECT is_castable('123' as numeric) // true

SELECT is_castable(1.5 as int) // true

SELECT is_castable('1.5' as int) // false

Many users write their own functions:

https://stackoverflow.com/q/10306830/2446102 (11k views, ~25 upvotes)

https://stackoverflow.com/q/36775814/2446102

https://stackoverflow.com/a/16206123/2446102 (72k views, 70 upvotes)

https://stackoverflow.com/q/2082686/2446102 (174k views, ~150 upvotes)

Similar features are implemented in:

- SQL Server (as TRY_CONVERT)

- Oracle (as CONVERT([val] DEFAULT [expr] ON CONVERSION ERROR)

I would love to implement it myself, but my knowledge of C is superficial.

Thanks,

Michał Wadas

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