Qualified column names

A qualifier for a column name can be a table name, a view name, an alias name, a synonym, or a correlation name. Whether a column name can be qualified depends, like its meaning, on its context.

• In some forms of the COMMENT and LABEL statements, a column name must be qualified. This is shown in the syntax diagrams.
• Where the column name specifies values of the column, a column name can be qualified at the user's option.
• In the column list of an INSERT statement, a column name can be qualified.
• In the assignment-clause of an UPDATE or a MERGE statement, a column name can be qualified.
• In all other contexts, a column name must not be qualified. This rule will be mentioned in the discussion of each statement to which it applies.

Where a qualifier is optional, it can serve two purposes. See Column name qualifiers to avoid ambiguity for details.