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yield-syntax.md

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Yield Clause and Statement

Keyword YIELD can be used as a clause in a FETCH or GO statement, or as a separate statement in PIPE, or as a single sentence for calculation.

As Clause (with GO-syntax)

YIELD
    [DISTINCT]
    <col_name> [AS <col_alias>]
    [, <col_name> [AS <col_alias>] ...]

YIELD is commonly used to return results generated with GO (Refer GO).

nebula> GO FROM 201 OVER relations_edge YIELD $$.student.name AS Friend,\
        $$.student.age AS Age, $$.student.gender AS Gender
=========================
| Friend | Age | Gender |
=========================
|   Jane |  17 | female |
-------------------------

For example: $$.student.name is used to get the properties of the dest vertex ($$).

As Statement

Reference Inputs or Variables

  • You can use the YIELD statement in PIPE.
  • You can use the YIELD statement to reference variables.
  • For statements that do not support YIELD statement, you can use it as a tool to control the outputs.
YIELD
    [DISTINCT]
    <col_name> [AS <col_alias>]
    [, <col_name> [AS <col_alias>] ...]
    [WHERE <conditions>]

nebula> GO FROM 201 OVER like YIELD like._dst AS id | YIELD $-.* WHERE $-.id == 200;

=========
| $-.id |
=========
| 200   |
---------

nebula> $var2 = GO FROM 200 OVER like;$var1 = GO FROM 201 OVER like; \
    YIELD $var1.* UNION YIELD $var2.*;

===================
| $var1.like._dst |
===================
| 200             |
-------------------
| 201             |
-------------------
| 202             |
-------------------

As Separate Statement

YIELD statement can be used independently to retrieve computation results without reference to any graph. You can use AS to rename an alias.

nebula> YIELD 1 + 1
=========
| (1+1) |
=========
| 2     |
---------

nebula> YIELD "Hel" + "\tlo" AS HELLO_1, ", World!" AS WORLD_2
======================
| HELLO_1 | WORLD_2  |
======================
| Hel  lo  | , World! |
----------------------

nebula> YIELD hash("Tim") % 100
=====================
| (hash("Tim")%100) |
=====================
| 42                |
---------------------

Note: You can not use YIELD DISTINCT as a separate statement. This is a syntax error.

nebula> YIELD DISTINCT 1     --- syntax error!