|Oracle® Database SQL Language Reference
12c Release 1 (12.1)
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The list of expressions that appears after the
SELECT keyword and before the
FROM clause is called the select list. Within the select list, you specify one or more columns in the set of rows you want Oracle Database to return from one or more tables, views, or materialized views. The number of columns, as well as their data type and length, are determined by the elements of the select list.
If two or more tables have some column names in common, then you must qualify column names with names of tables. Otherwise, fully qualified column names are optional. However, it is always a good idea to qualify table and column references explicitly. Oracle often does less work with fully qualified table and column names.
You can use a column alias,
c_alias, to label the immediately preceding expression in the select list so that the column is displayed with a new heading. The alias effectively renames the select list item for the duration of the query. The alias can be used in the
BY clause, but not other clauses in the query.
You can use comments in a
SELECT statement to pass instructions, or hints, to the Oracle Database optimizer. The optimizer uses hints to choose an execution plan for the statement. Refer to "Hints" for more information on hints.