Indexes can usually be created for both primary and secondary keys.

More Questions from Introduction to SQL

• Scalar aggregate are multiple values returned from an SQL query that includes an aggregate function.
• Data manipulation language (DML) commands are used to define a database, including creating, altering, and dropping tables and establishing constraints.
• DISTINCT and its counterpart, ALL, can be used more than once in a SELECT statement.
• SELECT DISTINCT is used if a user wishes to see duplicate columns in a query.
• The SQL statement: SELECT Name, COUNT(*) FROM NAME_TABLE; counts the number of name rows and displays this total in a table with a single row and a single column.
• The qualifier DISTINCT must be used in an SQL statement when we want to eliminate duplicate rows.
• There is an equivalent join expression that can be substituted for all subquery expressions.
• The ADD command is used to enter one row of data or to add multiple rows as a result of a query.
• The result of every SQL query is a table.
• The rows of the result relation produced by a SELECT statement can be sorted, but only by one column.

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