DuckDB is a strongly typed database system. As such, every column has a single type specified. This type is constant
over the entire column. That is to say, a column that is labeled as an INTEGER column will only contain INTEGER
values.
DuckDB also supports columns of composite types. For example, it is possible to define an array of integers (INTEGER[]). It is also possible to define types as arbitrary structs (ROW(i INTEGER, j VARCHAR)). For that reason, native DuckDB type objects are not mere enums, but a class that can potentially be nested.
Types in the C API are modeled using an enum (duckdb_type) and a complex class (duckdb_logical_type). For most primitive types, e.g., integers or varchars, the enum is sufficient. For more complex types, such as lists, structs or decimals, the logical type must be used.
typedef enum DUCKDB_TYPE {
DUCKDB_TYPE_INVALID = 0,
DUCKDB_TYPE_BOOLEAN = 1,
DUCKDB_TYPE_TINYINT = 2,
DUCKDB_TYPE_SMALLINT = 3,
DUCKDB_TYPE_INTEGER = 4,
DUCKDB_TYPE_BIGINT = 5,
DUCKDB_TYPE_UTINYINT = 6,
DUCKDB_TYPE_USMALLINT = 7,
DUCKDB_TYPE_UINTEGER = 8,
DUCKDB_TYPE_UBIGINT = 9,
DUCKDB_TYPE_FLOAT = 10,
DUCKDB_TYPE_DOUBLE = 11,
DUCKDB_TYPE_TIMESTAMP = 12,
DUCKDB_TYPE_DATE = 13,
DUCKDB_TYPE_TIME = 14,
DUCKDB_TYPE_INTERVAL = 15,
DUCKDB_TYPE_HUGEINT = 16,
DUCKDB_TYPE_UHUGEINT = 32,
DUCKDB_TYPE_VARCHAR = 17,
DUCKDB_TYPE_BLOB = 18,
DUCKDB_TYPE_DECIMAL = 19,
DUCKDB_TYPE_TIMESTAMP_S = 20,
DUCKDB_TYPE_TIMESTAMP_MS = 21,
DUCKDB_TYPE_TIMESTAMP_NS = 22,
DUCKDB_TYPE_ENUM = 23,
DUCKDB_TYPE_LIST = 24,
DUCKDB_TYPE_STRUCT = 25,
DUCKDB_TYPE_MAP = 26,
DUCKDB_TYPE_ARRAY = 33,
DUCKDB_TYPE_UUID = 27,
DUCKDB_TYPE_UNION = 28,
DUCKDB_TYPE_BIT = 29,
DUCKDB_TYPE_TIME_TZ = 30,
DUCKDB_TYPE_TIMESTAMP_TZ = 31,
} duckdb_type;
Functions
The enum type of a column in the result can be obtained using the duckdb_column_type function. The logical type of a column can be obtained using the duckdb_column_logical_type function.
duckdb_value
The duckdb_value functions will auto-cast values as required. For example, it is no problem to use
duckdb_value_double on a column of type duckdb_value_int32. The value will be auto-cast and returned as a double.
Note that in certain cases the cast may fail. For example, this can happen if we request a duckdb_value_int8 and the value does not fit within an int8 value. In this case, a default value will be returned (usually 0 or nullptr). The same default value will also be returned if the corresponding value is NULL.
The duckdb_value_is_null function can be used to check if a specific value is NULL or not.
The exception to the auto-cast rule is the duckdb_value_varchar_internal function. This function does not auto-cast and only works for VARCHAR columns. The reason this function exists is that the result does not need to be freed.
duckdb_value_varcharandduckdb_value_blobrequire the result to be de-allocated usingduckdb_free.
duckdb_fetch_chunk
The duckdb_fetch_chunk function can be used to read data chunks from a DuckDB result set, and is the most efficient way of reading data from a DuckDB result using the C API. It is also the only way of reading data of certain types from a DuckDB result. For example, the duckdb_value functions do not support structural reading of composite types (lists or structs) or more complex types like enums and decimals.
For more information about data chunks, see the documentation on data chunks.
API Reference Overview
duckdb_data_chunk duckdb_result_get_chunk(duckdb_result result, idx_t chunk_index);
bool duckdb_result_is_streaming(duckdb_result result);
idx_t duckdb_result_chunk_count(duckdb_result result);
duckdb_result_type duckdb_result_return_type(duckdb_result result);
Date Time Timestamp Helpers
duckdb_date_struct duckdb_from_date(duckdb_date date);
duckdb_date duckdb_to_date(duckdb_date_struct date);
bool duckdb_is_finite_date(duckdb_date date);
duckdb_time_struct duckdb_from_time(duckdb_time time);
duckdb_time_tz duckdb_create_time_tz(int64_t micros, int32_t offset);
duckdb_time_tz_struct duckdb_from_time_tz(duckdb_time_tz micros);
duckdb_time duckdb_to_time(duckdb_time_struct time);
duckdb_timestamp_struct duckdb_from_timestamp(duckdb_timestamp ts);
duckdb_timestamp duckdb_to_timestamp(duckdb_timestamp_struct ts);
bool duckdb_is_finite_timestamp(duckdb_timestamp ts);
Hugeint Helpers
double duckdb_hugeint_to_double(duckdb_hugeint val);
duckdb_hugeint duckdb_double_to_hugeint(double val);
Decimal Helpers
duckdb_decimal duckdb_double_to_decimal(double val, uint8_t width, uint8_t scale);
double duckdb_decimal_to_double(duckdb_decimal val);
Logical Type Interface
duckdb_logical_type duckdb_create_logical_type(duckdb_type type);
char *duckdb_logical_type_get_alias(duckdb_logical_type type);
void duckdb_logical_type_set_alias(duckdb_logical_type type, const char *alias);
duckdb_logical_type duckdb_create_list_type(duckdb_logical_type type);
duckdb_logical_type duckdb_create_array_type(duckdb_logical_type type, idx_t array_size);
duckdb_logical_type duckdb_create_map_type(duckdb_logical_type key_type, duckdb_logical_type value_type);
duckdb_logical_type duckdb_create_union_type(duckdb_logical_type *member_types, const char **member_names, idx_t member_count);
duckdb_logical_type duckdb_create_struct_type(duckdb_logical_type *member_types, const char **member_names, idx_t member_count);
duckdb_logical_type duckdb_create_enum_type(const char **member_names, idx_t member_count);
duckdb_logical_type duckdb_create_decimal_type(uint8_t width, uint8_t scale);
duckdb_type duckdb_get_type_id(duckdb_logical_type type);
uint8_t duckdb_decimal_width(duckdb_logical_type type);
uint8_t duckdb_decimal_scale(duckdb_logical_type type);
duckdb_type duckdb_decimal_internal_type(duckdb_logical_type type);
duckdb_type duckdb_enum_internal_type(duckdb_logical_type type);
uint32_t duckdb_enum_dictionary_size(duckdb_logical_type type);
char *duckdb_enum_dictionary_value(duckdb_logical_type type, idx_t index);
duckdb_logical_type duckdb_list_type_child_type(duckdb_logical_type type);
duckdb_logical_type duckdb_array_type_child_type(duckdb_logical_type type);
idx_t duckdb_array_type_array_size(duckdb_logical_type type);
duckdb_logical_type duckdb_map_type_key_type(duckdb_logical_type type);
duckdb_logical_type duckdb_map_type_value_type(duckdb_logical_type type);
idx_t duckdb_struct_type_child_count(duckdb_logical_type type);
char *duckdb_struct_type_child_name(duckdb_logical_type type, idx_t index);
duckdb_logical_type duckdb_struct_type_child_type(duckdb_logical_type type, idx_t index);
idx_t duckdb_union_type_member_count(duckdb_logical_type type);
char *duckdb_union_type_member_name(duckdb_logical_type type, idx_t index);
duckdb_logical_type duckdb_union_type_member_type(duckdb_logical_type type, idx_t index);
void duckdb_destroy_logical_type(duckdb_logical_type *type);
duckdb_state duckdb_register_logical_type(duckdb_connection con, duckdb_logical_type type, duckdb_create_type_info info);
duckdb_result_get_chunk
Warning Deprecation notice. This method is scheduled for removal in a future release.
Fetches a data chunk from the duckdb_result. This function should be called repeatedly until the result is exhausted.
The result must be destroyed with duckdb_destroy_data_chunk.
This function supersedes all duckdb_value functions, as well as the duckdb_column_data and duckdb_nullmask_data
functions. It results in significantly better performance, and should be preferred in newer code-bases.
If this function is used, none of the other result functions can be used and vice versa (i.e., this function cannot be mixed with the legacy result functions).
Use duckdb_result_chunk_count to figure out how many chunks there are in the result.
Syntax
duckdb_data_chunk duckdb_result_get_chunk(
duckdb_result result,
idx_t chunk_index
);
Parameters
result: The result object to fetch the data chunk from.chunk_index: The chunk index to fetch from.
Return Value
The resulting data chunk. Returns NULL if the chunk index is out of bounds.
duckdb_result_is_streaming
Warning Deprecation notice. This method is scheduled for removal in a future release.
Checks if the type of the internal result is StreamQueryResult.
Syntax
bool duckdb_result_is_streaming(
duckdb_result result
);
Parameters
result: The result object to check.
Return Value
Whether or not the result object is of the type StreamQueryResult
duckdb_result_chunk_count
Warning Deprecation notice. This method is scheduled for removal in a future release.
Returns the number of data chunks present in the result.
Syntax
idx_t duckdb_result_chunk_count(
duckdb_result result
);
Parameters
result: The result object
Return Value
Number of data chunks present in the result.
duckdb_result_return_type
Returns the return_type of the given result, or DUCKDB_RETURN_TYPE_INVALID on error
Syntax
duckdb_result_type duckdb_result_return_type(
duckdb_result result
);
Parameters
result: The result object
Return Value
The return_type
duckdb_from_date
Decompose a duckdb_date object into year, month and date (stored as duckdb_date_struct).
Syntax
duckdb_date_struct duckdb_from_date(
duckdb_date date
);
Parameters
date: The date object, as obtained from aDUCKDB_TYPE_DATEcolumn.
Return Value
The duckdb_date_struct with the decomposed elements.
duckdb_to_date
Re-compose a duckdb_date from year, month and date (duckdb_date_struct).
Syntax
duckdb_date duckdb_to_date(
duckdb_date_struct date
);
Parameters
date: The year, month and date stored in aduckdb_date_struct.
Return Value
The duckdb_date element.
duckdb_is_finite_date
Test a duckdb_date to see if it is a finite value.
Syntax
bool duckdb_is_finite_date(
duckdb_date date
);
Parameters
date: The date object, as obtained from aDUCKDB_TYPE_DATEcolumn.
Return Value
True if the date is finite, false if it is ±infinity.
duckdb_from_time
Decompose a duckdb_time object into hour, minute, second and microsecond (stored as duckdb_time_struct).
Syntax
duckdb_time_struct duckdb_from_time(
duckdb_time time
);
Parameters
time: The time object, as obtained from aDUCKDB_TYPE_TIMEcolumn.
Return Value
The duckdb_time_struct with the decomposed elements.
duckdb_create_time_tz
Create a duckdb_time_tz object from micros and a timezone offset.
Syntax
duckdb_time_tz duckdb_create_time_tz(
int64_t micros,
int32_t offset
);
Parameters
micros: The microsecond component of the time.offset: The timezone offset component of the time.
Return Value
The duckdb_time_tz element.
duckdb_from_time_tz
Decompose a TIME_TZ objects into micros and a timezone offset.
Use duckdb_from_time to further decompose the micros into hour, minute, second and microsecond.
Syntax
duckdb_time_tz_struct duckdb_from_time_tz(
duckdb_time_tz micros
);
Parameters
micros: The time object, as obtained from aDUCKDB_TYPE_TIME_TZcolumn.
duckdb_to_time
Re-compose a duckdb_time from hour, minute, second and microsecond (duckdb_time_struct).
Syntax
duckdb_time duckdb_to_time(
duckdb_time_struct time
);
Parameters
time: The hour, minute, second and microsecond in aduckdb_time_struct.
Return Value
The duckdb_time element.
duckdb_from_timestamp
Decompose a duckdb_timestamp object into a duckdb_timestamp_struct.
Syntax
duckdb_timestamp_struct duckdb_from_timestamp(
duckdb_timestamp ts
);
Parameters
ts: The ts object, as obtained from aDUCKDB_TYPE_TIMESTAMPcolumn.
Return Value
The duckdb_timestamp_struct with the decomposed elements.
duckdb_to_timestamp
Re-compose a duckdb_timestamp from a duckdb_timestamp_struct.
Syntax
duckdb_timestamp duckdb_to_timestamp(
duckdb_timestamp_struct ts
);
Parameters
ts: The de-composed elements in aduckdb_timestamp_struct.
Return Value
The duckdb_timestamp element.
duckdb_is_finite_timestamp
Test a duckdb_timestamp to see if it is a finite value.
Syntax
bool duckdb_is_finite_timestamp(
duckdb_timestamp ts
);
Parameters
ts: The timestamp object, as obtained from aDUCKDB_TYPE_TIMESTAMPcolumn.
Return Value
True if the timestamp is finite, false if it is ±infinity.
duckdb_hugeint_to_double
Converts a duckdb_hugeint object (as obtained from a DUCKDB_TYPE_HUGEINT column) into a double.
Syntax
double duckdb_hugeint_to_double(
duckdb_hugeint val
);
Parameters
val: The hugeint value.
Return Value
The converted double element.
duckdb_double_to_hugeint
Converts a double value to a duckdb_hugeint object.
If the conversion fails because the double value is too big the result will be 0.
Syntax
duckdb_hugeint duckdb_double_to_hugeint(
double val
);
Parameters
val: The double value.
Return Value
The converted duckdb_hugeint element.
duckdb_double_to_decimal
Converts a double value to a duckdb_decimal object.
If the conversion fails because the double value is too big, or the width/scale are invalid the result will be 0.
Syntax
duckdb_decimal duckdb_double_to_decimal(
double val,
uint8_t width,
uint8_t scale
);
Parameters
val: The double value.
Return Value
The converted duckdb_decimal element.
duckdb_decimal_to_double
Converts a duckdb_decimal object (as obtained from a DUCKDB_TYPE_DECIMAL column) into a double.
Syntax
double duckdb_decimal_to_double(
duckdb_decimal val
);
Parameters
val: The decimal value.
Return Value
The converted double element.
duckdb_create_logical_type
Creates a duckdb_logical_type from a primitive type.
The resulting logical type must be destroyed with duckdb_destroy_logical_type.
Returns an invalid logical type, if type is: DUCKDB_TYPE_INVALID, DUCKDB_TYPE_DECIMAL, DUCKDB_TYPE_ENUM,
DUCKDB_TYPE_LIST, DUCKDB_TYPE_STRUCT, DUCKDB_TYPE_MAP, DUCKDB_TYPE_ARRAY, or DUCKDB_TYPE_UNION.
Syntax
duckdb_logical_type duckdb_create_logical_type(
duckdb_type type
);
Parameters
type: The primitive type to create.
Return Value
The logical type.
duckdb_logical_type_get_alias
Returns the alias of a duckdb_logical_type, if set, else nullptr.
The result must be destroyed with duckdb_free.
Syntax
char *duckdb_logical_type_get_alias(
duckdb_logical_type type
);
Parameters
type: The logical type
Return Value
The alias or nullptr
duckdb_logical_type_set_alias
Sets the alias of a duckdb_logical_type.
Syntax
void duckdb_logical_type_set_alias(
duckdb_logical_type type,
const char *alias
);
Parameters
type: The logical typealias: The alias to set
duckdb_create_list_type
Creates a LIST type from its child type.
The return type must be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_list_type(
duckdb_logical_type type
);
Parameters
type: The child type of the list
Return Value
The logical type.
duckdb_create_array_type
Creates an ARRAY type from its child type.
The return type must be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_array_type(
duckdb_logical_type type,
idx_t array_size
);
Parameters
type: The child type of the array.array_size: The number of elements in the array.
Return Value
The logical type.
duckdb_create_map_type
Creates a MAP type from its key type and value type.
The return type must be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_map_type(
duckdb_logical_type key_type,
duckdb_logical_type value_type
);
Parameters
key_type: The map's key type.value_type: The map's value type.
Return Value
The logical type.
duckdb_create_union_type
Creates a UNION type from the passed arrays.
The return type must be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_union_type(
duckdb_logical_type *member_types,
const char **member_names,
idx_t member_count
);
Parameters
member_types: The array of union member types.member_names: The union member names.member_count: The number of union members.
Return Value
The logical type.
duckdb_create_struct_type
Creates a STRUCT type based on the member types and names.
The resulting type must be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_struct_type(
duckdb_logical_type *member_types,
const char **member_names,
idx_t member_count
);
Parameters
member_types: The array of types of the struct members.member_names: The array of names of the struct members.member_count: The number of members of the struct.
Return Value
The logical type.
duckdb_create_enum_type
Creates an ENUM type from the passed member name array.
The resulting type should be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_enum_type(
const char **member_names,
idx_t member_count
);
Parameters
member_names: The array of names that the enum should consist of.member_count: The number of elements that were specified in the array.
Return Value
The logical type.
duckdb_create_decimal_type
Creates a DECIMAL type with the specified width and scale.
The resulting type should be destroyed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_create_decimal_type(
uint8_t width,
uint8_t scale
);
Parameters
width: The width of the decimal typescale: The scale of the decimal type
Return Value
The logical type.
duckdb_get_type_id
Retrieves the enum duckdb_type of a duckdb_logical_type.
Syntax
duckdb_type duckdb_get_type_id(
duckdb_logical_type type
);
Parameters
type: The logical type.
Return Value
The duckdb_type id.
duckdb_decimal_width
Retrieves the width of a decimal type.
Syntax
uint8_t duckdb_decimal_width(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The width of the decimal type
duckdb_decimal_scale
Retrieves the scale of a decimal type.
Syntax
uint8_t duckdb_decimal_scale(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The scale of the decimal type
duckdb_decimal_internal_type
Retrieves the internal storage type of a decimal type.
Syntax
duckdb_type duckdb_decimal_internal_type(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The internal type of the decimal type
duckdb_enum_internal_type
Retrieves the internal storage type of an enum type.
Syntax
duckdb_type duckdb_enum_internal_type(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The internal type of the enum type
duckdb_enum_dictionary_size
Retrieves the dictionary size of the enum type.
Syntax
uint32_t duckdb_enum_dictionary_size(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The dictionary size of the enum type
duckdb_enum_dictionary_value
Retrieves the dictionary value at the specified position from the enum.
The result must be freed with duckdb_free.
Syntax
char *duckdb_enum_dictionary_value(
duckdb_logical_type type,
idx_t index
);
Parameters
type: The logical type objectindex: The index in the dictionary
Return Value
The string value of the enum type. Must be freed with duckdb_free.
duckdb_list_type_child_type
Retrieves the child type of the given LIST type. Also accepts MAP types.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_list_type_child_type(
duckdb_logical_type type
);
Parameters
type: The logical type, either LIST or MAP.
Return Value
The child type of the LIST or MAP type.
duckdb_array_type_child_type
Retrieves the child type of the given ARRAY type.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_array_type_child_type(
duckdb_logical_type type
);
Parameters
type: The logical type. Must be ARRAY.
Return Value
The child type of the ARRAY type.
duckdb_array_type_array_size
Retrieves the array size of the given array type.
Syntax
idx_t duckdb_array_type_array_size(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The fixed number of elements the values of this array type can store.
duckdb_map_type_key_type
Retrieves the key type of the given map type.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_map_type_key_type(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The key type of the map type. Must be destroyed with duckdb_destroy_logical_type.
duckdb_map_type_value_type
Retrieves the value type of the given map type.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_map_type_value_type(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The value type of the map type. Must be destroyed with duckdb_destroy_logical_type.
duckdb_struct_type_child_count
Returns the number of children of a struct type.
Syntax
idx_t duckdb_struct_type_child_count(
duckdb_logical_type type
);
Parameters
type: The logical type object
Return Value
The number of children of a struct type.
duckdb_struct_type_child_name
Retrieves the name of the struct child.
The result must be freed with duckdb_free.
Syntax
char *duckdb_struct_type_child_name(
duckdb_logical_type type,
idx_t index
);
Parameters
type: The logical type objectindex: The child index
Return Value
The name of the struct type. Must be freed with duckdb_free.
duckdb_struct_type_child_type
Retrieves the child type of the given struct type at the specified index.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_struct_type_child_type(
duckdb_logical_type type,
idx_t index
);
Parameters
type: The logical type objectindex: The child index
Return Value
The child type of the struct type. Must be destroyed with duckdb_destroy_logical_type.
duckdb_union_type_member_count
Returns the number of members that the union type has.
Syntax
idx_t duckdb_union_type_member_count(
duckdb_logical_type type
);
Parameters
type: The logical type (union) object
Return Value
The number of members of a union type.
duckdb_union_type_member_name
Retrieves the name of the union member.
The result must be freed with duckdb_free.
Syntax
char *duckdb_union_type_member_name(
duckdb_logical_type type,
idx_t index
);
Parameters
type: The logical type objectindex: The child index
Return Value
The name of the union member. Must be freed with duckdb_free.
duckdb_union_type_member_type
Retrieves the child type of the given union member at the specified index.
The result must be freed with duckdb_destroy_logical_type.
Syntax
duckdb_logical_type duckdb_union_type_member_type(
duckdb_logical_type type,
idx_t index
);
Parameters
type: The logical type objectindex: The child index
Return Value
The child type of the union member. Must be destroyed with duckdb_destroy_logical_type.
duckdb_destroy_logical_type
Destroys the logical type and de-allocates all memory allocated for that type.
Syntax
void duckdb_destroy_logical_type(
duckdb_logical_type *type
);
Parameters
type: The logical type to destroy.
duckdb_register_logical_type
Registers a custom type within the given connection. The type must have an alias
Syntax
duckdb_state duckdb_register_logical_type(
duckdb_connection con,
duckdb_logical_type type,
duckdb_create_type_info info
);
Parameters
con: The connection to usetype: The custom type to register
Return Value
Whether or not the registration was successful.