Execute an arbitrary SQL statement against the chDB session.

Use ClickHouse SQL dialect. Common formats: JSONCompact (default), CSVWithNames, TabSeparatedWithNames, Pretty. The result is truncated at CHDB_MCP_MAX_RESULT_BYTES (default 1 MiB) and the query is aborted after CHDB_MCP_QUERY_TIMEOUT_SEC seconds (default 30).

Args: sql: Any read-only SQL (SELECT/SHOW/DESCRIBE/EXPLAIN). Writes require CHDB_MCP_WRITE=1. When CHDB_MCP_FILE_ALLOWLIST is set, any table function that isn't on the safe-by-construction list (numbers/values/view/merge/dictionary/etc.) is rejected — that includes file/url/s3/remote/executable/python and every other external-reach function chDB exposes. Use query_file() for files instead. format: Output format passed to chDB. Defaults to JSONCompact.

List databases visible to the chDB session.

Returns one database name per line (TabSeparated format).

List tables in a given database.

Args: database: Database name. Must be a plain SQL identifier (letters, digits, underscore — no quotes, dots, or spaces).

Return column types for a table.

Args: database: Database name (plain identifier). table: Table name (plain identifier).

Query a local file (Parquet/CSV/JSON/…) as if it were a table.

The literal token {file} in sql is substituted with a file('path', 'format') table-function call before execution.

Example::

query_file(
    path="/data/sales.parquet",
    sql="SELECT region, sum(revenue) FROM {file} GROUP BY region",
    format="Parquet",
)

Args: path: Filesystem path. If CHDB_MCP_FILE_ALLOWLIST is set, the resolved path must sit under one of its prefixes. sql: Query body. Must contain the literal placeholder {file}. When CHDB_MCP_FILE_ALLOWLIST is set, the SQL is scanned before substitution; any extra table function call other than the placeholder (e.g. a UNION with file('/etc/passwd', ...) or a stray url()/executable()) is rejected. format: chDB file format hint. Common values: Parquet, CSV, CSVWithNames, JSONEachRow, Arrow.

Return the first N rows of a table.

Args: database: Database name (plain identifier). table: Table name (plain identifier). limit: Maximum rows. Clamped to [1, 1000].

List SQL functions available in the chDB engine.

Returns name, is_aggregate, case_insensitive, alias_to for each entry in system.functions — useful for agents discovering ClickHouse's 1000+ function library (windowFunnel, quantilesTDigest, -If/-State/-Merge combinators, etc.) in one round trip.

Args: pattern: Optional case-insensitive substring filter on the function name. Plain text only; SQL wildcards and quotes are escaped.