hash function

The hash() function returns the hash value of the argument. The argument can be a number, a string, a list, a boolean, null, or an expression that evaluates to a value of the preceding data types.

The source code of the hash() function (MurmurHash2), seed (0xc70f6907UL), and other parameters can be found in MurmurHash2.h.

For Java, the hash function operates as follows.

MurmurHash2.hash64("to_be_hashed".getBytes(),"to_be_hashed".getBytes().length, 0xc70f6907)

Legacy version compatibility

In nGQL 1.0, when nGQL does not support string VIDs, a common practice is to hash the strings first and then use the values as VIDs. But in nGQL 2.0, both string VIDs and integer VIDs are supported, so there is no need to use hash() to set VIDs.

Hash a number

nebula> YIELD hash(-123);
+--------------+
| hash(-(123)) |
+--------------+
| -123         |
+--------------+

Hash a string

nebula> YIELD hash("to_be_hashed");
+----------------------+
| hash(to_be_hashed)   |
+----------------------+
| -1098333533029391540 |
+----------------------+

Hash a list

nebula> YIELD hash([1,2,3]);
+----------------+
| hash([1,2,3])  |
+----------------+
| 11093822460243 |
+----------------+

Hash a boolean

nebula> YIELD hash(true);
+------------+
| hash(true) |
+------------+
| 1          |
+------------+

nebula> YIELD hash(false);
+-------------+
| hash(false) |
+-------------+
| 0           |
+-------------+

Hash NULL

nebula> YIELD hash(NULL);
+------------+
| hash(NULL) |
+------------+
| -1         |
+------------+

Hash an expression

nebula> YIELD hash(toLower("HELLO NEBULA"));
+-------------------------------+
| hash(toLower("HELLO NEBULA")) |
+-------------------------------+
| -8481157362655072082          |
+-------------------------------+

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Last update: January 14, 2022