anchor.diff:  
   [[create_index_syntax]]
   === Syntax Description of CREATE INDEX
  +* `VOLATILE`
  ++
  +The CREATE VOLATILE INDEX statement creates an SQL index with a lifespan that is limited to the SQL session that the index is created. Volatile indexes are dropped automatically when the session ends. See <<indexes,Indexes>>.
  +
  +* `UNIQUE`
  ++
  +The CREATE UNIQUE INDEX statement creates a unique index on a table and enforces uniqueness for the indexed field, that is, it imposes the restriction that any duplicate column values are disallowed and must be eliminated before creating a unique index on a column. 
  +
  ++
  +Unique index not only improves the query performance, but also provides data integrity checking. The constraint is checked when rows of the table are inserted or updated.
  +
  ++
  +NOTE: Multiple NULL values are treated as duplicate values for a column which can contain only one NULL value.
   
   * `_index_`
   +
  
positive.code: ```
  CREATE PRIVATE SCHEMA AUTHORIZATION JSmith;
  ```
  
  <<<
  [[create_table_statement]]
  
negative.code: an SQL identifier containing the name of a statement already prepared in this session. An SQL identifier is
  case-insensitive (will be in uppercase) unless it is double-quoted. It must be double-quoted if it contains blanks,
  lowercase letters, or special characters. It must start with a letter. When you refer to the prepared query in a
  SELECT statement, you must use uppercase.
  
  Note: A few non-reserved words that can be used for prepared statement names cannot be used directly in EXPLAIN.
  For example, 'EXPLAIN access;' results in a syntax error. You can still use the name, however, by using a
  delimited identifier. That is, specify the name in upper case, surrounded by double-quotes. For example,
  'EXPLAIN "ACCESS";' will work.
  
  * `_query-text_`
  +
  specifies the text of a query.
  