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5.3.2 Column Labels

The entries in the select list can be assigned names for further processing. The “further processing” in this case is an optional sort specification and the client application (e.g., column headers for display). For example:

SELECT a AS value, b + c AS sum FROM ...

If no output column name is specified using AS, the system assigns a default name. For simple column references, this is the name of the referenced column. For function calls, this is the name of the function. For complex expressions, the system will generate a generic name.

Note: The naming of output columns here is different from that done in the FROM clause (see section 5.2.1.2 Table and Column Aliases). This pipeline will in fact allow you to rename the same column twice, but the name chosen in the select list is the one that will be passed on.