## 10.6. `SELECT` Output Columns

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The rules given in the preceding sections will result in assignment
of non-`unknown` data types to all expressions in an SQL query,
except for unspecified-type literals that appear as simple output
columns of a `SELECT` command. For example, in

```
SELECT 'Hello World';

```

 there is nothing to identify what type the string literal should be
taken as. In this situation PostgreSQL will fall back
to resolving the literal's type as `text`.

When the `SELECT` is one arm of a `UNION`(or `INTERSECT` or `EXCEPT`) construct, or when it
appears within `INSERT ... SELECT`, this rule is not applied
since rules given in preceding sections take precedence. The type of an
unspecified-type literal can be taken from the other `UNION` arm
in the first case, or from the destination column in the second case.

`RETURNING` lists are treated the same as `SELECT`output lists for this purpose.

### Note

 Prior to PostgreSQL 10, this rule did not exist, and unspecified-type literals in a `SELECT` output list were left as type `unknown`. That had assorted bad consequences, so it's been changed.

