Added halfvec example for OpenAI [skip ci]

Author: ankane

examples/openai/halfvec.py

@@ -0,0 +1,34 @@
+from openai import OpenAI
+from pgvector.psycopg import register_vector, HalfVector
+import psycopg
+
+conn = psycopg.connect(dbname='pgvector_example', autocommit=True)
+
+conn.execute('CREATE EXTENSION IF NOT EXISTS vector')
+register_vector(conn)
+
+conn.execute('DROP TABLE IF EXISTS documents')
+conn.execute('CREATE TABLE documents (id bigserial PRIMARY KEY, content text, embedding halfvec(3072))')
+conn.execute('CREATE INDEX ON documents USING hnsw (embedding halfvec_cosine_ops)')
+
+
+def embed(input):
+    client = OpenAI()
+    response = client.embeddings.create(input=input, model='text-embedding-3-large')
+    return [v.embedding for v in response.data]
+
+
+input = [
+    'The dog is barking',
+    'The cat is purring',
+    'The bear is growling'
+]
+embeddings = embed(input)
+for content, embedding in zip(input, embeddings):
+    conn.execute('INSERT INTO documents (content, embedding) VALUES (%s, %s)', (content, HalfVector(embedding)))
+
+query = 'forest'
+query_embedding = embed([query])[0]
+result = conn.execute('SELECT content FROM documents ORDER BY embedding <=> %s LIMIT 5', (HalfVector(query_embedding),)).fetchall()
+for row in result:
+    print(row[0])