create_aggregate(name, num_params, aggregate_class)
Creates a user-defined aggregate function.
The aggregate class must implement a step method, which accepts the number of parameters num_params (if num_params is -1, the function may take any number of arguments), and a finalize method which will return the final result of the aggregate.
The finalize method can return any of the types supported by SQLite: bytes, str, int, float and None.
Example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | import sqlite3class MySum: def __init__(self): self.count = 0 def step(self, value): self.count += value def finalize(self): return self.countcon = sqlite3.connect(":memory:")con.create_aggregate("mysum", 1, MySum)cur = con.cursor()cur.execute("create table test(i)")cur.execute("insert into test(i) values (1)")cur.execute("insert into test(i) values (2)")cur.execute("select mysum(i) from test")print(cur.fetchone()[0]) |
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