J Lumby <johnlu...@hotmail.com> writes: > I am curious about the syntactic nature of the expression : > TIMESTAMP '2020-07-13' > in this expression, is the token TIMESTAMP a function, typecast, or other? > I don't see a description of it as a function and there are no > parentheses in this example.
This construct is a typed constant, as described at "4.1.2.7. Constants Of Other Types" on this page: https://www.postgresql.org/docs/current/sql-syntax-lexical.html It's a wart, frankly, and we wouldn't have it if the SQL standard didn't insist. Of the three syntaxes described by 4.1.2.7: type 'string' 'string'::type CAST ( 'string' AS type ) the second and third actually work for casting any expression, but the first one *only* works for a literal-string constant. People are constantly burnt by that, for example by expecting that they can write TIMESTAMP $1 You can plug a parameter symbol into the other two syntaxes, but not that one. On the whole I prefer using 'string'::type, which is slightly more typing effort, but it generalizes correctly. > I also tried > FLOAT8 '7.3' > and that is accepted as well. IIRC, the SQL standard only defines this syntax for certain types such as TIMESTAMP and INTERVAL; but Postgres allows it for any type name. regards, tom lane
