docs: Separate config from notebooks, add PostgreSQL compatibility

Changes:
- Remove environment variable configuration from notebooks
  (DataJoint reads DJ_* env vars automatically)
- Add conftest.py to configure DataJoint for pytest runs
- Fix boolean aggregation in 04-queries.ipynb to work on both backends
  (use CASE WHEN instead of sum(boolean))
- Add PostgreSQL skip to json-type.ipynb (requires MySQL JSON functions)

Test results:
- MySQL: 21/21 passed
- PostgreSQL: 20/20 passed, 1 skipped (json-type)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

conftest.py

@@ -0,0 +1,35 @@
+"""
+Pytest configuration for notebook tests.
+
+Configures DataJoint from environment variables before any tests run.
+This separates configuration from workflow execution.
+
+Usage:
+    # MySQL (default)
+    DJ_HOST=localhost DJ_USER=root DJ_PASS=tutorial pytest --nbmake ...
+
+    # PostgreSQL
+    DJ_HOST=localhost DJ_PORT=5432 DJ_USER=datajoint DJ_PASS=tutorial DJ_BACKEND=postgresql pytest --nbmake ...
+"""
+
+import os
+
+
+def pytest_configure(config):
+    """Configure DataJoint from environment variables before tests run."""
+    import datajoint as dj
+
+    # Database connection settings
+    if os.getenv('DJ_HOST'):
+        dj.config['database.host'] = os.getenv('DJ_HOST')
+    if os.getenv('DJ_PORT'):
+        dj.config['database.port'] = int(os.getenv('DJ_PORT'))
+    if os.getenv('DJ_USER'):
+        dj.config['database.user'] = os.getenv('DJ_USER')
+    if os.getenv('DJ_PASS'):
+        dj.config['database.password'] = os.getenv('DJ_PASS')
+    if os.getenv('DJ_BACKEND'):
+        dj.config['database.backend'] = os.getenv('DJ_BACKEND')
+
+    # Display settings for notebooks
+    dj.config['display.limit'] = 8

src/how-to/model-relationships.ipynb

@@ -31,7 +31,7 @@
      ]
     }
    ],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('howto_relationships')\nschema.drop(prompt=False)\nschema = dj.Schema('howto_relationships')"
+   "source": "import datajoint as dj\n\nschema = dj.Schema('howto_relationships')\nschema.drop(prompt=False)\nschema = dj.Schema('howto_relationships')"
   },
   {
    "cell_type": "markdown",

src/how-to/read-diagrams.ipynb

@@ -36,7 +36,7 @@
      ]
     }
    ],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('howto_diagrams')\nschema.drop(prompt=False)\nschema = dj.Schema('howto_diagrams')"
+   "source": "import datajoint as dj\n\nschema = dj.Schema('howto_diagrams')\nschema.drop(prompt=False)\nschema = dj.Schema('howto_diagrams')"
   },
   {
    "cell_type": "markdown",

src/tutorials/advanced/custom-codecs.ipynb

@@ -35,7 +35,7 @@
      ]
     }
    ],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nimport numpy as np\n\nschema = dj.Schema('tutorial_codecs')"
+   "source": "import datajoint as dj\n\nimport numpy as np\n\nschema = dj.Schema('tutorial_codecs')"
   },
   {
    "cell_type": "markdown",

src/tutorials/advanced/distributed.ipynb

@@ -36,7 +36,7 @@
      ]
     }
    ],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nimport numpy as np\nimport time\n\nschema = dj.Schema('tutorial_distributed')\n\n# Clean up from previous runs\nschema.drop(prompt=False)\nschema = dj.Schema('tutorial_distributed')"
+   "source": "import datajoint as dj\n\nimport numpy as np\nimport time\n\nschema = dj.Schema('tutorial_distributed')\n\n# Clean up from previous runs\nschema.drop(prompt=False)\nschema = dj.Schema('tutorial_distributed')"
   },
   {
    "cell_type": "markdown",

src/tutorials/advanced/json-type.ipynb

@@ -42,7 +42,7 @@
     }
    },
    "outputs": [],
-   "source": "import datajoint as dj\nimport os\n\n# Configure database connection from environment variables (for CI/testing)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\n# Check if running against PostgreSQL - skip this MySQL-specific tutorial"
+   "source": "import datajoint as dj\n\n# Skip this tutorial when running against PostgreSQL\n# (requires MySQL 8.0+ for JSON_VALUE function)\nimport pytest\nif dj.config.database.backend == 'postgresql':\n    pytest.skip(\"JSON tutorial requires MySQL 8.0+ (uses MySQL-specific JSON functions)\", allow_module_level=True)"
   },
   {
    "cell_type": "markdown",

src/tutorials/advanced/sql-comparison.ipynb

@@ -34,7 +34,7 @@
     }
    },
    "outputs": [],
-   "source": "import datajoint as dj\nimport os\n\n# Configure database connection from environment variables (for CI/testing)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('tutorial_sql_comparison')"
+   "source": "import datajoint as dj\n\n# Configure database connection from environment variables (for CI/testing)\n\nschema = dj.Schema('tutorial_sql_comparison')"
   },
   {
    "cell_type": "markdown",

src/tutorials/basics/01-first-pipeline.ipynb

@@ -39,7 +39,7 @@
     }
    },
    "outputs": [],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('tutorial_first_pipeline')"
+   "source": "import datajoint as dj\n\nschema = dj.Schema('tutorial_first_pipeline')"
   },
   {
    "cell_type": "markdown",

src/tutorials/basics/02-schema-design.ipynb

@@ -36,7 +36,7 @@
      ]
     }
    ],
-   "source": "import datajoint as dj\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('tutorial_design')"
+   "source": "import datajoint as dj\n\nschema = dj.Schema('tutorial_design')"
   },
   {
    "cell_type": "markdown",

src/tutorials/basics/03-data-entry.ipynb

@@ -30,7 +30,7 @@
     }
    },
    "outputs": [],
-   "source": "import datajoint as dj\nimport numpy as np\nimport os\n\n# Configure from environment variables (for testing with different backends)\nif os.getenv('DJ_HOST'):\n    dj.config['database.host'] = os.getenv('DJ_HOST')\nif os.getenv('DJ_PORT'):\n    dj.config['database.port'] = int(os.getenv('DJ_PORT'))\nif os.getenv('DJ_USER'):\n    dj.config['database.user'] = os.getenv('DJ_USER')\nif os.getenv('DJ_PASS'):\n    dj.config['database.password'] = os.getenv('DJ_PASS')\n\nschema = dj.Schema('tutorial_data_entry')"
+   "source": "import datajoint as dj\nimport numpy as np\n\nschema = dj.Schema('tutorial_data_entry')"
   },
   {
    "cell_type": "code",