LIMIT AND SKIP¶
The LIMIT clause constrains the number of rows in the output. The usage of LIMIT in native nGQL statements and openCypher compatible statements is different.
- Native nGQL: Generally, a pipe
|needs to be used before theLIMITclause. The offset parameter can be set or omitted directly after theLIMITstatement.
- OpenCypher compatible statements: No pipes are permitted before the
LIMITclause. And you can useSKIPto indicate an offset.
Note
When using LIMIT in either syntax above, it is important to use an ORDER BY clause that constrains the output into a unique order. Otherwise, you will get an unpredictable subset of the output.
LIMIT in native nGQL statements¶
In native nGQL, LIMIT has general syntax and exclusive syntax in GO statements.
General LIMIT syntax in native nGQL statements¶
In native nGQL, the general LIMIT syntax works the same as in SQL. The LIMIT clause accepts one or two parameters. The values of both parameters must be non-negative integers and be used after a pipe. The syntax and description are as follows:
... | LIMIT [<offset>,] <number_rows>;
| Parameter | Description |
|---|---|
offset |
The offset value. It defines the row from which to start returning. The offset starts from 0. The default value is 0, which returns from the first row. |
number_rows |
It constrains the total number of returned rows. |
For example:
# The following example returns the top 3 rows of data from the result.
nebula> LOOKUP ON player YIELD id(vertex)|\
LIMIT 3;
+-------------+
| id(VERTEX) |
+-------------+
| "player100" |
| "player101" |
| "player102" |
+-------------+
# The following example returns the 3 rows of data starting from the second row of the sorted output.
nebula> GO FROM "player100" OVER follow REVERSELY \
YIELD properties($$).name AS Friend, properties($$).age AS Age \
| ORDER BY $-.Age, $-.Friend \
| LIMIT 1, 3;
+-------------------+-----+
| Friend | Age |
+-------------------+-----+
| "Danny Green" | 31 |
| "Aron Baynes" | 32 |
| "Marco Belinelli" | 32 |
+-------------------+-----+
LIMIT in GO statements¶
In addition to the general syntax in the native nGQL, the LIMIT in the GO statement also supports limiting the number of output results based on edges.
Syntax:
<go_statement> LIMIT <limit_list>;
limit_list is a list. Elements in the list must be natural numbers, and the number of elements must be the same as the maximum number of STEPS in the GO statement. The following takes GO 1 TO 3 STEPS FROM "A" OVER * LIMIT <limit_list> as an example to introduce this usage of LIMIT in detail.
- The list
limit_listmust contain 3 natural numbers, such asGO 1 TO 3 STEPS FROM "A" OVER * LIMIT [1,2,4]. 1inLIMIT [1,2,4]means that the system automatically selects 1 edge to continue traversal in the first step.2means to select 2 edges to continue traversal in the second step.4indicates that 4 edges are selected to continue traversal in the third step.- Because
GO 1 TO 3 STEPSmeans to return all the traversal results from the first to third steps, all the red edges and their source and destination vertices in the figure below will be matched by thisGOstatement. And the yellow edges represent there is no path selected when the GO statement traverses. If it is notGO 1 TO 3 STEPSbutGO 3 STEPS, it will only match the red edges of the third step and the vertices at both ends.
In the basketballplayer dataset, the example is as follows:
nebula> GO 3 STEPS FROM "player100" \
OVER * \
YIELD properties($$).name AS NAME, properties($$).age AS Age \
LIMIT [3,3,3];
+-----------------+----------+
| NAME | Age |
+-----------------+----------+
| "Tony Parker" | 36 |
| "Manu Ginobili" | 41 |
| "Spurs" | __NULL__ |
+-----------------+----------+
nebula> GO 3 STEPS FROM "player102" OVER * BIDIRECT\
YIELD dst(edge) \
LIMIT [rand32(5),rand32(5),rand32(5)];
+-------------+
| dst(EDGE) |
+-------------+
| "player100" |
| "player100" |
+-------------+
LIMIT in openCypher compatible statements¶
In openCypher compatible statements such as MATCH, there is no need to use a pipe when LIMIT is used. The syntax and description are as follows:
... [SKIP <offset>] [LIMIT <number_rows>];
| Parameter | Description |
|---|---|
offset |
The offset value. It defines the row from which to start returning. The offset starts from 0. The default value is 0, which returns from the first row. |
number_rows |
It constrains the total number of returned rows. |
Both offset and number_rows accept expressions, but the result of the expression must be a non-negative integer.
Note
Fraction expressions composed of two integers are automatically floored to integers. For example, 8/6 is floored to 1.
Examples of LIMIT¶
LIMIT can be used alone to return a specified number of results.
nebula> MATCH (v:player) RETURN v.player.name AS Name, v.player.age AS Age \
ORDER BY Age LIMIT 5;
+-------------------------+-----+
| Name | Age |
+-------------------------+-----+
| "Luka Doncic" | 20 |
| "Ben Simmons" | 22 |
| "Kristaps Porzingis" | 23 |
| "Giannis Antetokounmpo" | 24 |
| "Kyle Anderson" | 25 |
+-------------------------+-----+
Examples of SKIP¶
SKIP can be used alone to set the offset and return the data after the specified position.
nebula> MATCH (v:player{name:"Tim Duncan"}) --> (v2) \
RETURN v2.player.name AS Name, v2.player.age AS Age \
ORDER BY Age DESC SKIP 1;
+-----------------+-----+
| Name | Age |
+-----------------+-----+
| "Manu Ginobili" | 41 |
| "Tony Parker" | 36 |
+-----------------+-----+
nebula> MATCH (v:player{name:"Tim Duncan"}) --> (v2) \
RETURN v2.player.name AS Name, v2.player.age AS Age \
ORDER BY Age DESC SKIP 1+1;
+---------------+-----+
| Name | Age |
+---------------+-----+
| "Tony Parker" | 36 |
+---------------+-----+
Example of SKIP and LIMIT¶
SKIP and LIMIT can be used together to return the specified amount of data starting from the specified position.
nebula> MATCH (v:player{name:"Tim Duncan"}) --> (v2) \
RETURN v2.player.name AS Name, v2.player.age AS Age \
ORDER BY Age DESC SKIP 1 LIMIT 1;
+-----------------+-----+
| Name | Age |
+-----------------+-----+
| "Manu Ginobili" | 41 |
+-----------------+-----+