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          |
+-------------------------------+

Last update: August 27, 2021