Dataflow SQL lexical structure

A Cloud Dataflow SQL statement comprises a series of tokens. Tokens include identifiers, quoted identifiers, literals, keywords, operators, and special characters. Tokens can be separated by whitespace (space, backspace, tab, newline) or comments.

Identifiers

Identifiers are names that are associated with columns, tables, and other database objects.

There are two ways to specify an identifier: unquoted or quoted:

• Unquoted identifiers must begin with a letter or an underscore. Subsequent characters can be letters, numbers, or underscores.
• Quoted identifiers are enclosed by backtick (`) characters and can contain any character, such as spaces or symbols. However, quoted identifiers cannot be empty. Reserved Keywords can only be used as identifiers if enclosed by backticks.

Syntax (presented as a grammar with regular expressions, ignoring whitespace):

identifier: { quoted_identifier | unquoted_identifier }
unquoted_identifier: [A-Za-z_][A-Za-z_0-9]*
quoted_identifier: \`[^\\\`\r\n] any_escape* \`
any_escape: \\(. | \n | \r | \r\n)

Examples:

Customers5
_dataField1
ADGROUP

Invalid examples:

5Customers
_dataField!
GROUP

5Customers begins with a number, not a letter or underscore. _dataField! contains the special character "!" which is not a letter, number, or underscore. GROUP is a reserved keyword, and therefore cannot be used as an identifier without being enclosed by backtick characters.

Both identifiers and quoted identifiers are case insensitive, with some nuances. See Case Sensitivity for further details.

Quoted identifiers have the same escape sequences as string literals, defined below.

Literals

A literal represents a constant value of a built-in data type. Some, but not all, data types can be expressed as literals.

String and Bytes Literals

Both string and bytes literals must be quoted, either with single (') or double (") quotation marks, or triple-quoted with groups of three single (''') or three double (""") quotation marks.

Quoted literals:

Prefix characters (r, R, b, B) are optional for quoted or triple-quoted strings, and indicate that the string is a raw/regex string or a byte sequence, respectively. For example, b'abc' and b'''abc''' are both interpreted as type bytes. Prefix characters are case insensitive.

Quoted literals with prefixes:

The table below lists all valid escape sequences for representing non-alphanumeric characters in string literals. Any sequence not in this table produces an error.

Integer Literals

Integer literals are either a sequence of decimal digits (0 through 9) or a hexadecimal value that is prefixed with "0x". Integers can be prefixed by "+" or "-" to represent positive and negative values, respectively.

Examples:

123
0xABC
-123

An integer literal is interpreted as an INT64.

Floating Point Literals

Syntax options:

[+-]DIGITS.[DIGITS][e[+-]DIGITS]
[DIGITS].DIGITS[e[+-]DIGITS]
DIGITSe[+-]DIGITS

DIGITS represents one or more decimal numbers (0 through 9) and e represents the exponent marker (e or E).

Examples:

123.456e-67
.1E4
58.
4e2

Numeric literals that contain either a decimal point or an exponent marker are presumed to be type double.

Implicit coercion of floating point literals to float type is possible if the value is within the valid float range.

There is no literal representation of NaN or infinity.

Array Literals

Array literals are a comma-separated lists of elements enclosed in square brackets. The ARRAY keyword is optional, and an explicit element type T is also optional.

Examples:

[1, 2, 3]
['x', 'y', 'xy']
ARRAY[1, 2, 3]
ARRAY<string>['x', 'y', 'xy']

Timestamp literals

Syntax:

TIMESTAMP 'YYYY-[M]M-[D]D [[H]H:[M]M:[S]S[.DDDDDD]] [timezone]'

Timestamp literals contain the TIMESTAMP keyword and a string literal that conforms to the canonical timestamp format, enclosed in single quotation marks.

Timestamp literals support a range between the years 1 and 9999, inclusive. Timestamps outside of this range are invalid.

A timestamp literal can include a numerical suffix to indicate the timezone:

TIMESTAMP '2014-09-27 12:30:00.45-08'

If this suffix is absent, the default timezone, UTC, is used.

For example, the following timestamp represents 12:30 p.m. on September 27, 2014, using the timezone, UTC:

TIMESTAMP '2014-09-27 12:30:00.45'

For more information on timezones, see Timezone.

String literals with the canonical timestamp format, including those with timezone names, implicitly coerce to a timestamp literal when used where a timestamp expression is expected. For example, in the following query, the string literal "2014-09-27 12:30:00.45 America/Los_Angeles" is coerced to a timestamp literal.

SELECT * FROM foo
WHERE timestamp_col = "2014-09-27 12:30:00.45 America/Los_Angeles"

Timezone

Since timestamp literals must be mapped to a specific point in time, a timezone is necessary to correctly interpret a literal. If a timezone is not specified as part of the literal itself, then the default timezone value, which is set by the Cloud Dataflow SQL implementation, is used.

Timezones are represented by strings in the following canonical format, which represents the offset from Coordinated Universal Time (UTC).

Format:

(+|-)H[H][:M[M]]

Examples:

'-08:00'
'-8:15'
'+3:00'
'+07:30'
'-7'

Timezones can also be expressed using string timezone names from the tz database. For a less comprehensive but simpler reference, see the List of tz database timezones on Wikipedia. Canonical timezone names have the format <continent/[region/]city>, such as America/Los_Angeles.

Note that not all timezone names are interchangeable even if they do happen to report the same time during a given part of the year. For example, America/Los_Angeles reports the same time as UTC-7:00 during Daylight Savings Time, but reports the same time as UTC-8:00 outside of Daylight Savings Time.

Example:

TIMESTAMP '2014-09-27 12:30:00 America/Los_Angeles'
TIMESTAMP '2014-09-27 12:30:00 America/Argentina/Buenos_Aires'

Case Sensitivity

Cloud Dataflow SQL follows these rules for case sensitivity:

Reserved Keywords

Keywords are a group of tokens that have special meaning in the Cloud Dataflow SQL language, and have the following characteristics:

• Keywords cannot be used as identifiers unless enclosed by backtick (`) characters.
• Keywords are case insensitive.

Cloud Dataflow SQL has the following reserved keywords.

Terminating Semicolons

Statements can optionally use a terminating semicolon (;) in the context of a query string submitted through an Application Programming Interface (API). Some interactive tools require statements to have a terminating semicolon. In a request containing multiple statements, statements must be separated by semicolons, but the semicolon is optional for the final statement.

Comments

Comments are sequences of characters that are ignored by the parser. Cloud Dataflow SQL supports the following types of comments.

Single line comments

Single line comments are supported by prepending # or -- before the comment.

Examples

SELECT x FROM T; # x is a field and T is a table

Comment includes all characters from the '#' character to the end of the line.

SELECT x FROM T; --x is a field and T is a table

Comment includes all characters from the '--' sequence to the end of the line. You can optionally add a space after the '--'.

Multiline comments

Multiline comments are supported by enclosing the comment using /* <comment> */.

Example:

SELECT x FROM T /* x is a field and T is a table */
WHERE x = 3;

Invalid example:

SELECT x FROM T /* comment starts here
                /* comment ends on this line */
                this line is not considered a comment */
WHERE x = 3;

Comment includes all characters, including newlines, enclosed by the first occurrence of '/*' and the first subsequent occurrence of '*/'. Nested comments are not supported. The second example contains a nested comment that renders the query invalid.