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Tuple Join

Syntax

SELECT target_list
  FROM stream_identifier_1 '[' {window_identifier_1|window_specification} ']'
       [[AS] stream_alias_1], stream_identifier_2
       '[' {window_identifier_2|window_specification} ']'
       [[AS] stream_alias_2]
  WHERE predicate

Substitutable Fields

target_list:

One or more entries, separated by commas, of the format target_list_entry.

target_list_entry:

A value, of the format scalar_expression [[AS] output_field_identifier], to be included in the result set returned by the statement. Values may be obtained from a tuple field or from a simple function. Optionally, the name for a value may be modified through an alias.

scalar_expression:

A value that will be included in the output tuple. Fields from either input tuple may be included in the output tuple. If desired, the output field may be renamed using an alias.

output_field_identifier:

An optional name (alias) for a value in the result set. Alias names must be used for values derived from functions.

stream_identifier:

The streams containing the input tuples. Each stream must be windowed; the corresponding window is identified within the required square brackets that follow each stream_identifier.

window_identifier:

A named window specification previously declared with a CREATE WINDOW statement. Both streams may use the same window specification, or they may be associated with different window specifications. Note that the square braces are a required part of the syntax.

window_specification:

A window specification defined within the FROM clause. Both streams may use the same window specification, or they may be associated with different window specifications. Note that the square braces are a required part of the syntax.

stream_alias:

An optional alias name for a stream.

predicate:

A conditional statement that establishes the constraints for the join, for example, stream_alias_1.field_identifier==stream_alias_2.field_identifier.

Discussion

A tuple-based join is a SELECT statement in which the FROM clause includes two windowed stream entries. Within the window specifications, ADVANCE must have the value one. The WHERE clause establishes the constraints that will be used to select tuples for joining.

If the window specification associated with a stream includes a TIMEOUT clause, tuples will be dropped from the stream's buffer after the timeout period has elapsed and will no longer be available for matching.

A tuple-based join generates a stream and may be used anywhere a stream expression is acceptable. Alternatively, the output could be "captured" in a stream, as illustrated in the following code fragments.

CREATE [OUTPUT] STREAM stream_identifier;
SELECT ... INTO stream_identifier;

CREATE [OUTPUT] STREAM stream_identifier AS
  SELECT ...;

Or, for an OUTPUT STREAM

SELECT ... => CREATE OUTPUT STREAM stream_identifier;