Question:
What is the ora_hash function
and how do I use it?
Answer:
ora_hash is a function that computes a hash value for a
given expression. This function has 3 parameters: expr;
max_bucket; and seed_value. The expr
parameter determines the data that you want Oracle to compute a hash
for, and it can be any type or length of data. max_bucket
and seed_value are both optional. The first can be any
number between 0 and 4294967295 and defaults to the latter.
seed_value enables Oracle to produce different results for the
same set of data, and while it has the same upper and lower bounds
as max_bucket, the default for seed_value is 0.
The ora_hash function returns a NUMBER value.
The following example creates a hash for each combination of
customer ID and product ID from the sh.sales tables, divides the
hash values into 100 different buckets, and then returns the sum of
the amount_sold values in the first bucket. By adding or
changing a seed_value, you can get different hash results
from the same query.
SELECT SUM(amount_sold) FROM sales
WHERE ORA_HASH(CONCAT(cust_id, prod_id), 99) = 0;
SUM(AMOUNT_SOLD)
----------------
7315
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