How to read a syntax diagram
Applies to: 
Databricks SQL Databricks Runtime
This section describes the various patterns of syntax used throughout the SQL reference.
Base components
Keyword
SELECT
Keywords in SQL are always capitalized in this document, but they are case insensitive.
Token
( )
< >
.
*
,
The SQL language includes round braces ((, )) as well as angled braces (<, >),
dots (.), commas (,), and a few other characters. When these characters are
present in a syntax diagram you must enter them as is.
Clause
LIMIT clause
SELECT named_expression
named_expression
expression AS alias
A clause represents a named subsection of syntax. A local clause is described
in the same syntax diagram that invokes it. If the clause is common, it links to
another section of the Databricks SQL reference. Some clauses are known by their main
keyword and are depicted with a capital keyword followed by clause. Other
clauses are always lower case and use underscore (_) where appropriate.
Local clauses are fully explained within the following section.
All other clauses have a short description with a link to the main page.
Argument
mapExpr
Arguments to functions are specified in camelCase. Databricks SQL describes the meaning of arguments in the Arguments section.
Chain of tokens
SELECT expr
Components separated by whitespace must be entered in order, unconditionally,
and be separated only by whitespace or comments. Databricks SQL supports comments of
the form /* ... */ (C-style), and -- ..., which extends to end of the line.
Choice
Specifies a fork in the syntax.
Mandatory choice
{ INT | INTEGER }
Curly braces { ... } mean you must specify exactly one of the multiple components.
Each choice is separated by a |.
Optional choice
[ ASC | DESC ]
Square brackets [ ... ] indicate you can choose at most one of multiple components.
Each choice is separated by a |.
Grouping
{ SELECT expr }
{ SELECT
expr }
Curly braces { ... } specify that you must provide all the embedded components.
If a syntax diagram spans multiple lines, this form clarifies that it depicts the same syntax.
Option
[ NOT NULL ]
Square brackets [...] specify that the enclosed components are optional.
Repetition
col_option [...]
col_alias [, ...]
{ expr [ AS ] col_alias } [, ...]
The [...] ellipsis notation indicates that you can repeat the immediately preceding component, grouping, or choice multiple times.
If the ellipsis is preceded by another character, such as a separated dot [. ...], or a comma [, ...], you must separate each repetition by that character.