How to read the syntax diagrams

The following rules apply to the syntax diagrams used in this book.

• Read the syntax diagrams from left to right, from top to bottom, following the path of the line.

  The ►►─── symbol indicates the beginning of the syntax diagram.

  The ───► symbol indicates that the syntax is continued on the next line.

  The ►─── symbol indicates that the syntax is continued from the previous line.

  The ───►◄ symbol indicates the end of the syntax diagram.

  Diagrams of syntactical units start with the |─── symbol and end with the ───| symbol.

• Required items appear on the horizontal line (the main path).

  
  >>-required_item-----------------------------------------------><
  
  

• Optional items appear below the main path.

  
  >>-required_item--+---------------+----------------------------><
                    '-optional_item-'   
  
  

  If an item appears above the main path, that item is optional, and has no effect on the execution of the statement and is used only for readability.

  
                    .-optional_item-.   
  >>-required_item--+---------------+----------------------------><
  
  

• If more than one item can be chosen, they appear vertically, in a stack.

  If one of the items must be chosen, one item of the stack appears on the main path.

  
  >>-required_item--+-required_choice-+--------------------------><
                    '-required_choice-'   
  
  

  If choosing one of the items is optional, the entire stack appears below the main path.

  
  >>-required_item--+-----------------+--------------------------><
                    +-optional_choice-+   
                    '-optional_choice-'   
  
  

  If one of the items is the default, it will appear above the main path and the remaining choices will be shown below.

  
                    .-default_choice--.   
  >>-required_item--+-----------------+--------------------------><
                    +-optional_choice-+   
                    '-optional_choice-'   
  
  

  If an optional item has a default when it is not specified, the default appears above the main path.

  
  >>-required_item--+--------------------------------------+-----><
                    |                  .-default_choice--. |   
                    +-optional_choice--+-required_choice-+-+   
                    |                  '-required_choice-' |   
                    '-optional_choice----------------------'   
  
  

• An arrow returning to the left, above the main line, indicates an item that can be repeated.

  
                    .-----------------.   
                    V                 |   
  >>-required_item----repeatable_item-+--------------------------><
  
  

  If the repeat arrow contains a comma, you must separate repeated items with a comma.

  
                    .-,---------------.   
                    V                 |   
  >>-required_item----repeatable_item-+--------------------------><
  
  

  A repeat arrow above a stack indicates that the items in the stack can be repeated.

• Keywords appear in uppercase (for example, FROM). They must be spelled exactly as shown. Variables appear in all lowercase letters (for example, column-name). They represent user-supplied names or values.
• If punctuation marks, parentheses, arithmetic operators, or other such symbols are shown, you must enter them as part of the syntax.