Double colon (::) notation in SQL

Have picked up someone's code and this is a part of a where clause, anyone know what the double colon indicates?

b.date_completed >  a.dc::date + INTERVAL '1 DAY 7:20:00'

It varies based on RDBMS, but if I guess right, that's PostgreSQL, in which case the :: converts a.dc to a date type of date.

In other flavors...

In MS SQL Server 2000:

> For built-in user-defined functions > that return a table, the function name > must be specified with a leading > double colon (::) to distinguish it > from user-defined functions that are > not built-in. It also must be > specified as a one-part name with no > database or owner qualifications. For > example: SELECT * FROM > ::fn_helpcollations() b.. For built-in > user-defined functions that return a > scalar value, the function name must > be specified as a one-part name (do > not specify database or owner). Do not > specify a leading double colon (::).

In MS SQL Server 2005:

> Double-colons are no longer required > for UDFs that return a table.

However...

> Double-colons are required in SQL > Server 2005 when granting permissions > on schemas, certificates, endpoints, > and a few other securables.

As well as...

> When using User-Defined Types, static > methods of the type must be called > using the double-colon syntax.

Sources: BOL and Kalen Delaney's Blog

In this case, it is a cast to a date type. :: is a type cast that can also be represented as CAST(expression AS type).

It is a CAST operation(cast to a date type).

Example:

SELECT now()::timestamp(0);

Is equivalent to:

SELECT 
    CAST (now() AS timestamp(0));

They both result in casting now() to timestamp in the following format: YYYY-MM-DD HH:MM:SS

It is probably a cast, converting a.dc to type date.

IBM Informix Dynamic Server (IDS) would work that way - but the INTERVAL notation at the end is not valid for IDS, so presumably this is in fact another DBMS (probably PostgreSQL).