--- layout: docu title: Table Functions --- The table function API can be used to define a table function that can then be called from within DuckDB in the `FROM` clause of a query. ## API Reference Overview

duckdb_table_function duckdb_create_table_function();
void duckdb_destroy_table_function(duckdb_table_function *table_function);
void duckdb_table_function_set_name(duckdb_table_function table_function, const char *name);
void duckdb_table_function_add_parameter(duckdb_table_function table_function, duckdb_logical_type type);
void duckdb_table_function_add_named_parameter(duckdb_table_function table_function, const char *name, duckdb_logical_type type);
void duckdb_table_function_set_extra_info(duckdb_table_function table_function, void *extra_info, duckdb_delete_callback_t destroy);
void duckdb_table_function_set_bind(duckdb_table_function table_function, duckdb_table_function_bind_t bind);
void duckdb_table_function_set_init(duckdb_table_function table_function, duckdb_table_function_init_t init);
void duckdb_table_function_set_local_init(duckdb_table_function table_function, duckdb_table_function_init_t init);
void duckdb_table_function_set_function(duckdb_table_function table_function, duckdb_table_function_t function);
void duckdb_table_function_supports_projection_pushdown(duckdb_table_function table_function, bool pushdown);
duckdb_state duckdb_register_table_function(duckdb_connection con, duckdb_table_function function);

### Table Function Bind

void *duckdb_bind_get_extra_info(duckdb_bind_info info);
void duckdb_bind_add_result_column(duckdb_bind_info info, const char *name, duckdb_logical_type type);
idx_t duckdb_bind_get_parameter_count(duckdb_bind_info info);
duckdb_value duckdb_bind_get_parameter(duckdb_bind_info info, idx_t index);
duckdb_value duckdb_bind_get_named_parameter(duckdb_bind_info info, const char *name);
void duckdb_bind_set_bind_data(duckdb_bind_info info, void *bind_data, duckdb_delete_callback_t destroy);
void duckdb_bind_set_cardinality(duckdb_bind_info info, idx_t cardinality, bool is_exact);
void duckdb_bind_set_error(duckdb_bind_info info, const char *error);

### Table Function Init

void *duckdb_init_get_extra_info(duckdb_init_info info);
void *duckdb_init_get_bind_data(duckdb_init_info info);
void duckdb_init_set_init_data(duckdb_init_info info, void *init_data, duckdb_delete_callback_t destroy);
idx_t duckdb_init_get_column_count(duckdb_init_info info);
idx_t duckdb_init_get_column_index(duckdb_init_info info, idx_t column_index);
void duckdb_init_set_max_threads(duckdb_init_info info, idx_t max_threads);
void duckdb_init_set_error(duckdb_init_info info, const char *error);

### Table Function

void *duckdb_function_get_extra_info(duckdb_function_info info);
void *duckdb_function_get_bind_data(duckdb_function_info info);
void *duckdb_function_get_init_data(duckdb_function_info info);
void *duckdb_function_get_local_init_data(duckdb_function_info info);
void duckdb_function_set_error(duckdb_function_info info, const char *error);

### `duckdb_create_table_function` Creates a new empty table function. The return value should be destroyed with `duckdb_destroy_table_function`. #### Syntax

duckdb_table_function duckdb_create_table_function(
  
);

#### Parameters * `returns` The table function object.
### `duckdb_destroy_table_function` Destroys the given table function object. #### Syntax

void duckdb_destroy_table_function(
  duckdb_table_function *table_function
);

#### Parameters * `table_function` The table function to destroy
### `duckdb_table_function_set_name` Sets the name of the given table function. #### Syntax

void duckdb_table_function_set_name(
  duckdb_table_function table_function,
  const char *name
);

#### Parameters * `table_function` The table function * `name` The name of the table function
### `duckdb_table_function_add_parameter` Adds a parameter to the table function. #### Syntax

void duckdb_table_function_add_parameter(
  duckdb_table_function table_function,
  duckdb_logical_type type
);

#### Parameters * `table_function` The table function * `type` The type of the parameter to add.
### `duckdb_table_function_add_named_parameter` Adds a named parameter to the table function. #### Syntax

void duckdb_table_function_add_named_parameter(
  duckdb_table_function table_function,
  const char *name,
  duckdb_logical_type type
);

#### Parameters * `table_function` The table function * `name` The name of the parameter * `type` The type of the parameter to add.
### `duckdb_table_function_set_extra_info` Assigns extra information to the table function that can be fetched during binding, etc. #### Syntax

void duckdb_table_function_set_extra_info(
  duckdb_table_function table_function,
  void *extra_info,
  duckdb_delete_callback_t destroy
);

#### Parameters * `table_function` The table function * `extra_info` The extra information * `destroy` The callback that will be called to destroy the bind data (if any)
### `duckdb_table_function_set_bind` Sets the bind function of the table function. #### Syntax

void duckdb_table_function_set_bind(
  duckdb_table_function table_function,
  duckdb_table_function_bind_t bind
);

#### Parameters * `table_function` The table function * `bind` The bind function
### `duckdb_table_function_set_init` Sets the init function of the table function. #### Syntax

void duckdb_table_function_set_init(
  duckdb_table_function table_function,
  duckdb_table_function_init_t init
);

#### Parameters * `table_function` The table function * `init` The init function
### `duckdb_table_function_set_local_init` Sets the thread-local init function of the table function. #### Syntax

void duckdb_table_function_set_local_init(
  duckdb_table_function table_function,
  duckdb_table_function_init_t init
);

#### Parameters * `table_function` The table function * `init` The init function
### `duckdb_table_function_set_function` Sets the main function of the table function. #### Syntax

void duckdb_table_function_set_function(
  duckdb_table_function table_function,
  duckdb_table_function_t function
);

#### Parameters * `table_function` The table function * `function` The function
### `duckdb_table_function_supports_projection_pushdown` Sets whether or not the given table function supports projection pushdown. If this is set to true, the system will provide a list of all required columns in the `init` stage through the `duckdb_init_get_column_count` and `duckdb_init_get_column_index` functions. If this is set to false (the default), the system will expect all columns to be projected. #### Syntax

void duckdb_table_function_supports_projection_pushdown(
  duckdb_table_function table_function,
  bool pushdown
);

#### Parameters * `table_function` The table function * `pushdown` True if the table function supports projection pushdown, false otherwise.
### `duckdb_register_table_function` Register the table function object within the given connection. The function requires at least a name, a bind function, an init function and a main function. If the function is incomplete or a function with this name already exists DuckDBError is returned. #### Syntax

duckdb_state duckdb_register_table_function(
  duckdb_connection con,
  duckdb_table_function function
);

#### Parameters * `con` The connection to register it in. * `function` The function pointer * `returns` Whether or not the registration was successful.
### `duckdb_bind_get_extra_info` Retrieves the extra info of the function as set in `duckdb_table_function_set_extra_info`. #### Syntax

void *duckdb_bind_get_extra_info(
  duckdb_bind_info info
);

#### Parameters * `info` The info object * `returns` The extra info
### `duckdb_bind_add_result_column` Adds a result column to the output of the table function. #### Syntax

void duckdb_bind_add_result_column(
  duckdb_bind_info info,
  const char *name,
  duckdb_logical_type type
);

#### Parameters * `info` The info object * `name` The name of the column * `type` The logical type of the column
### `duckdb_bind_get_parameter_count` Retrieves the number of regular (non-named) parameters to the function. #### Syntax

idx_t duckdb_bind_get_parameter_count(
  duckdb_bind_info info
);

#### Parameters * `info` The info object * `returns` The number of parameters
### `duckdb_bind_get_parameter` Retrieves the parameter at the given index. The result must be destroyed with `duckdb_destroy_value`. #### Syntax

duckdb_value duckdb_bind_get_parameter(
  duckdb_bind_info info,
  idx_t index
);

#### Parameters * `info` The info object * `index` The index of the parameter to get * `returns` The value of the parameter. Must be destroyed with `duckdb_destroy_value`.
### `duckdb_bind_get_named_parameter` Retrieves a named parameter with the given name. The result must be destroyed with `duckdb_destroy_value`. #### Syntax

duckdb_value duckdb_bind_get_named_parameter(
  duckdb_bind_info info,
  const char *name
);

#### Parameters * `info` The info object * `name` The name of the parameter * `returns` The value of the parameter. Must be destroyed with `duckdb_destroy_value`.
### `duckdb_bind_set_bind_data` Sets the user-provided bind data in the bind object. This object can be retrieved again during execution. #### Syntax

void duckdb_bind_set_bind_data(
  duckdb_bind_info info,
  void *bind_data,
  duckdb_delete_callback_t destroy
);

#### Parameters * `info` The info object * `extra_data` The bind data object. * `destroy` The callback that will be called to destroy the bind data (if any)
### `duckdb_bind_set_cardinality` Sets the cardinality estimate for the table function, used for optimization. #### Syntax

void duckdb_bind_set_cardinality(
  duckdb_bind_info info,
  idx_t cardinality,
  bool is_exact
);

#### Parameters * `info` The bind data object. * `is_exact` Whether or not the cardinality estimate is exact, or an approximation
### `duckdb_bind_set_error` Report that an error has occurred while calling bind. #### Syntax

void duckdb_bind_set_error(
  duckdb_bind_info info,
  const char *error
);

#### Parameters * `info` The info object * `error` The error message
### `duckdb_init_get_extra_info` Retrieves the extra info of the function as set in `duckdb_table_function_set_extra_info`. #### Syntax

void *duckdb_init_get_extra_info(
  duckdb_init_info info
);

#### Parameters * `info` The info object * `returns` The extra info
### `duckdb_init_get_bind_data` Gets the bind data set by `duckdb_bind_set_bind_data` during the bind. Note that the bind data should be considered as read-only. For tracking state, use the init data instead. #### Syntax

void *duckdb_init_get_bind_data(
  duckdb_init_info info
);

#### Parameters * `info` The info object * `returns` The bind data object
### `duckdb_init_set_init_data` Sets the user-provided init data in the init object. This object can be retrieved again during execution. #### Syntax

void duckdb_init_set_init_data(
  duckdb_init_info info,
  void *init_data,
  duckdb_delete_callback_t destroy
);

#### Parameters * `info` The info object * `extra_data` The init data object. * `destroy` The callback that will be called to destroy the init data (if any)
### `duckdb_init_get_column_count` Returns the number of projected columns. This function must be used if projection pushdown is enabled to figure out which columns to emit. #### Syntax

idx_t duckdb_init_get_column_count(
  duckdb_init_info info
);

#### Parameters * `info` The info object * `returns` The number of projected columns.
### `duckdb_init_get_column_index` Returns the column index of the projected column at the specified position. This function must be used if projection pushdown is enabled to figure out which columns to emit. #### Syntax

idx_t duckdb_init_get_column_index(
  duckdb_init_info info,
  idx_t column_index
);

#### Parameters * `info` The info object * `column_index` The index at which to get the projected column index, from 0..duckdb_init_get_column_count(info) * `returns` The column index of the projected column.
### `duckdb_init_set_max_threads` Sets how many threads can process this table function in parallel (default: 1) #### Syntax

void duckdb_init_set_max_threads(
  duckdb_init_info info,
  idx_t max_threads
);

#### Parameters * `info` The info object * `max_threads` The maximum amount of threads that can process this table function
### `duckdb_init_set_error` Report that an error has occurred while calling init. #### Syntax

void duckdb_init_set_error(
  duckdb_init_info info,
  const char *error
);

#### Parameters * `info` The info object * `error` The error message
### `duckdb_function_get_extra_info` Retrieves the extra info of the function as set in `duckdb_table_function_set_extra_info`. #### Syntax

void *duckdb_function_get_extra_info(
  duckdb_function_info info
);

#### Parameters * `info` The info object * `returns` The extra info
### `duckdb_function_get_bind_data` Gets the bind data set by `duckdb_bind_set_bind_data` during the bind. Note that the bind data should be considered as read-only. For tracking state, use the init data instead. #### Syntax

void *duckdb_function_get_bind_data(
  duckdb_function_info info
);

#### Parameters * `info` The info object * `returns` The bind data object
### `duckdb_function_get_init_data` Gets the init data set by `duckdb_init_set_init_data` during the init. #### Syntax

void *duckdb_function_get_init_data(
  duckdb_function_info info
);

#### Parameters * `info` The info object * `returns` The init data object
### `duckdb_function_get_local_init_data` Gets the thread-local init data set by `duckdb_init_set_init_data` during the local_init. #### Syntax

void *duckdb_function_get_local_init_data(
  duckdb_function_info info
);

#### Parameters * `info` The info object * `returns` The init data object
### `duckdb_function_set_error` Report that an error has occurred while executing the function. #### Syntax

void duckdb_function_set_error(
  duckdb_function_info info,
  const char *error
);

#### Parameters * `info` The info object * `error` The error message