The type resolution rules described in the preceding sections assign a non-unknown data type to every expression in a SQL query — with one exception: unspecified-type literals that appear as simple output columns of a SELECT command.
For example:
SELECT 'Hello World';Nothing in this statement constrains what type the string literal should be, so the database falls back to resolving it as text.
How context determines the type
The fallback-to-text rule applies only when a literal appears as a standalone SELECT output column. In other contexts, type resolution uses a different source:
| Context | How the type is resolved |
|---|---|
Standalone SELECT output column |
Falls back to text |
One arm of a UNION, INTERSECT, or EXCEPT |
Taken from the other arm |
INSERT ... SELECT |
Taken from the destination column |
In the UNION/INTERSECT/EXCEPT and INSERT ... SELECT cases, the rules described in the preceding sections take precedence, so the fallback rule does not apply.
RETURNING lists follow the same rules as SELECT output lists.