Expression

Expressions appear anywhere in SELECT statements, such as select_list, where clause, or group-by clause.

A expression is one of the following subsections.

Constant

Null constant

Null constant literal

NULL

Numeric constant

Currently, the following numeric literals are supported.

Integer constant literal

[0-9]+

Float constant literal

[0-9]+\.[0-9]+

Both are evaluated as minimal-sized signed value. For example, 1 is evaluated as SMALLINT, and 4294967296 (2^32) is evaluated as INTEGER.

String constant

A string constant UTF-8 string wrapped by ' (single quote). It is evaluated into a TEXT type.

String constant literal examples

'abc'
'abc  def'
'あいうえお'
'🍣'

Boolean constant

TRUE or FALSE.

Duration constant

Constructed from a function call prefixed DURATION_.

Column reference

A column in a stream can be referenced as follows:

Column reference

<stream name>.<column name>

Note that, currently, you cannot omit the stream name.

Special columns

For streams without ROWTIME keyword, the ptime special column is available to get the processing time of rows.

ptime

<stream name>.ptime

Operator invocation

An operator takes one (unary operator) or two (binary operator) operands.

A operand is also an expression.

Unary operator

<unary operator> <expression>

Binary operator

<expression> <binary operator> <expression>

• Unary operators:
  • -: Make the expression negative.
• Binary operators:
  • =: Check if two expressions are equal.
  • +: Add two expressions.
  • *: Multiply two expressions.
  • AND: Check if two expressions are both true.

Function call

A function call is composed of a function name and arguments.

Function call

<function name> (<arg1>, <arg2>, ...)

A function is evaluated in the row-by-row basis, unlike aggregate expressions.

Currently, these functions are available.

• DURATION_MILLIS(<integer>): Construct a DURATION type value from a integer number (milliseconds).
• DURATION_SECS(<integer>): Construct a DURATION type value from a integer number (seconds).
• FLOOR(<float>): Return the integer part of a float number.
• FLOOR_TIME(<timestamp>, <resolution (duration type)>): Return the timestamp rounded down to the nearest resolution.

Aggregate expression

An aggregate expression is composed of an aggregate function name and arguments.

Aggregate expression

<aggregate function name> (<arg1>, <arg2>, ...)

Aggregate expressions are called with window clauses. The final result of an aggregate expression is output when a window pane is closed.

Currently, these aggregate functions are available.

• AVG(<number>): Average of a number. Result is a float number.