Add connection based API example

Author: auxten

examples/connect.py

@@ -0,0 +1,122 @@
+"""
+chdb API Example - Demonstrating the Connection and Cursor interfaces
+This example shows common usage patterns with explanatory comments
+"""
+
+import chdb
+from datetime import datetime, date
+
+# 1. Creating a connection
+# The connect function supports several connection string formats:
+# - ":memory:" (in-memory database, default)
+# - "test.db" or "file:test.db" (relative path)
+# - "/path/to/test.db" or "file:/path/to/test.db" (absolute path)
+# - Connection strings can include query parameters: "file:test.db?param1=value1"
+
+# Create an in-memory connection
+conn = chdb.connect(":memory:")
+# Alternative: conn = chdb.connect("test.db")  # file-based connection
+
+# 2. Working with cursors
+# Cursors allow executing SQL queries and fetching results
+cursor = conn.cursor()
+
+# 3. Execute a simple query with multiple data types
+cursor.execute("""
+    SELECT 
+        42 as int_val,
+        3.14 as float_val,
+        'hello' as str_val,
+        true as bool_val,
+        NULL as null_val,
+        toDateTime('2024-03-20 15:30:00') as datetime_val,
+        toDate('2024-03-20') as date_val
+""")
+
+# 4. Fetch methods
+# 4.1. fetchone() - returns a single row as a tuple, or None if no more rows
+row = cursor.fetchone()
+print("Single row:", row)
+# Output example: (42, 3.14, 'hello', True, None, datetime(2024,3,20,15,30), date(2024,3,20))
+
+# 4.2. Execute a query with multiple rows
+cursor.execute("""
+    SELECT number, toString(number) as str_val 
+    FROM system.numbers 
+    LIMIT 5
+""")
+
+# fetchmany(size) - returns up to 'size' rows as a tuple of tuples
+batch = cursor.fetchmany(2)
+print("First 2 rows:", batch)
+# Output example: ((0, '0'), (1, '1'))
+
+# fetchall() - returns all remaining rows as a tuple of tuples
+remaining = cursor.fetchall()
+print("Remaining rows:", remaining)
+# Output example: ((2, '2'), (3, '3'), (4, '4'))
+
+# 5. Cursor as an iterator
+cursor.execute("SELECT number FROM system.numbers LIMIT 3")
+print("Iterating through cursor:")
+for row in cursor:
+    print(f"  Row: {row}")
+# Output:
+#   Row: (0,)
+#   Row: (1,)
+#   Row: (2,)
+
+# 6. Get metadata about the result set
+cursor.execute("""
+    SELECT 
+        42 as int_col,
+        'hello' as str_col, 
+        now() as time_col
+""")
+
+# 6.1. column_names() - get a list of column names
+col_names = cursor.column_names()
+print("Column names:", col_names)
+# Output example: ['int_col', 'str_col', 'time_col']
+
+# 6.2. column_types() - get a list of column types
+col_types = cursor.column_types()
+print("Column types:", col_types)
+# Output example: ['UInt8', 'String', 'DateTime']
+
+# 6.3. description - DB-API 2.0 compatible column descriptions
+# Format: list of 7-item tuples (name, type_code, display_size, internal_size, precision, scale, null_ok)
+# Only name and type_code are populated in this implementation
+desc = cursor.description
+print("Description:", desc)
+# Output example: [('int_col', 'UInt8', None, None, None, None, None), ...]
+
+# 7. Using the Connection.query() method for direct queries
+# This method returns results directly without needing to create a cursor
+
+# 7.1. Default format is CSV
+csv_result = conn.query("SELECT 1 as val, 'test' as name")
+print("CSV query result:", csv_result)
+# Returns data in CSV format as a string
+
+# 7.2. Using Arrow format to get a PyArrow table
+# Note: requires pyarrow to be installed
+arrow_result = conn.query("SELECT 1 as val, 'test' as name", format="Arrow") 
+print("Arrow query result type:", type(arrow_result))
+# Returns a PyArrow Table object
+
+# 7.3. Using DataFrame format to get a pandas DataFrame
+# Note: requires both pyarrow and pandas to be installed
+df_result = conn.query("SELECT 1 as val, 'test' as name", format="dataframe")
+print("DataFrame query result:\n", df_result)
+# Returns a pandas DataFrame
+
+# 8. Error handling
+try:
+    cursor.execute("SELECT non_existent_column")
+except Exception as e:
+    print("SQL Error:", e)
+
+# 9. Always close resources when done
+cursor.close()
+conn.close()