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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.