tasks/format-code-task-000043/instruction.md

Fix the following issue:

Fix DataFrame uploads with reserved/geometry columns

Uploading a pandas/geopandas DataFrame to CARTO via Dataset(df).upload(...) is generating inconsistent and sometimes broken SQL. For example, a DataFrame whose only columns are cartodb_id and the_geom ends up producing a CREATE TABLE statement with a dangling leading comma like CREATE TABLE t (, the_geom geometry(...)), which the database rejects. The root cause is that the column list used to create the table, the column list used in the COPY statement, and the values written to each row are all computed independently and can disagree about how many columns there are and what they are called.

Make the upload path derive a single, consistent description of the destination columns from the DataFrame and use it everywhere. The observable behavior of an upload (the CREATE TABLE statement and the COPY ... FROM stdin statement together with the rows of CSV data streamed to the backend) must satisfy the following contract.

Column selection and ordering

• Every column of the DataFrame is uploaded, in the DataFrame's original column order. In particular cartodb_id is treated as a normal column and is kept.
• A column named the_geom_webmercator (matched case-insensitively) is always dropped and never appears in the table, the COPY column list, or the data.

Geometry handling

• Exactly one column is treated as the geometry. If the DataFrame is a GeoDataFrame with an active geometry column, that column is used; otherwise the first column whose lower-cased name is one of the_geom, geom, geometry is used, considered in that order of priority (so if several are present, the_geom wins, then geom, then geometry).
• The chosen geometry column is named the_geom in the destination, declared with type geometry(<GeometryType>, 4326) where <GeometryType> is detected from the data (e.g. Point), and its values are emitted as SRID=4326;<WKT>. A null/missing geometry value produces an empty field.
• Any other column that merely happens to be named like a geometry but was not selected as the geometry column is uploaded as an ordinary column: it keeps its (normalized) name and its value is written verbatim, not re-encoded.

Ordinary columns

• Non-geometry column names are normalized to SQL-safe names (lower-cased, spaces and other unsupported characters replaced, etc.) in both the CREATE TABLE and the COPY column list. Values are written in their string form; a null value produces an empty field.
• Column SQL types in CREATE TABLE are derived from the DataFrame dtypes: float64/float32 → numeric, int64 → bigint, int32 → integer, object → text, bool → boolean, datetime dtypes → timestamp; anything else defaults to text.

with_lnglat

• When with_lnglat=(lng_col, lat_col) is passed, an extra geometry column named the_geom of type geometry(Point, 4326) is appended after the regular columns, built per row as SRID=4326;POINT (<lng> <lat>). The lng_col and lat_col columns are still uploaded as ordinary columns.
• When with_lnglat is used, any geometry column that would otherwise have been detected in the DataFrame is dropped, so the synthesized point is the only geometry uploaded.

Statement format

The COPY statement keeps its existing shape:

COPY <table>(<col1>,<col2>,...) FROM stdin WITH (FORMAT csv, DELIMITER '|');

with the destination column names joined by commas (no spaces). Each streamed row is the column values joined by | and terminated by a newline, encoded to bytes.