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 (INT[]). 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,
DUCKDB_TYPE_BOOLEAN,
DUCKDB_TYPE_TINYINT,
DUCKDB_TYPE_SMALLINT,
DUCKDB_TYPE_INTEGER,
DUCKDB_TYPE_BIGINT,
DUCKDB_TYPE_UTINYINT,
DUCKDB_TYPE_USMALLINT,
DUCKDB_TYPE_UINTEGER,
DUCKDB_TYPE_UBIGINT,
DUCKDB_TYPE_FLOAT,
DUCKDB_TYPE_DOUBLE,
DUCKDB_TYPE_TIMESTAMP,
DUCKDB_TYPE_DATE,
DUCKDB_TYPE_TIME,
DUCKDB_TYPE_INTERVAL,
DUCKDB_TYPE_HUGEINT,
DUCKDB_TYPE_VARCHAR,
DUCKDB_TYPE_BLOB,
DUCKDB_TYPE_DECIMAL,
DUCKDB_TYPE_TIMESTAMP_S,
DUCKDB_TYPE_TIMESTAMP_MS,
DUCKDB_TYPE_TIMESTAMP_NS,
DUCKDB_TYPE_ENUM,
DUCKDB_TYPE_LIST,
DUCKDB_TYPE_STRUCT,
DUCKDB_TYPE_MAP,
DUCKDB_TYPE_UUID,
DUCKDB_TYPE_JSON
} duckdb_type;
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.
Note that
duckdb_value_varcharandduckdb_value_blobrequire the result to be de-allocated usingduckdb_free.
duckdb_result_get_chunk
The duckdb_result_get_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
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);
bool duckdb_value_boolean(duckdb_result *result, idx_t col, idx_t row);
int8_t duckdb_value_int8(duckdb_result *result, idx_t col, idx_t row);
int16_t duckdb_value_int16(duckdb_result *result, idx_t col, idx_t row);
int32_t duckdb_value_int32(duckdb_result *result, idx_t col, idx_t row);
int64_t duckdb_value_int64(duckdb_result *result, idx_t col, idx_t row);
duckdb_hugeint duckdb_value_hugeint(duckdb_result *result, idx_t col, idx_t row);
duckdb_decimal duckdb_value_decimal(duckdb_result *result, idx_t col, idx_t row);
uint8_t duckdb_value_uint8(duckdb_result *result, idx_t col, idx_t row);
uint16_t duckdb_value_uint16(duckdb_result *result, idx_t col, idx_t row);
uint32_t duckdb_value_uint32(duckdb_result *result, idx_t col, idx_t row);
uint64_t duckdb_value_uint64(duckdb_result *result, idx_t col, idx_t row);
float duckdb_value_float(duckdb_result *result, idx_t col, idx_t row);
double duckdb_value_double(duckdb_result *result, idx_t col, idx_t row);
duckdb_date duckdb_value_date(duckdb_result *result, idx_t col, idx_t row);
duckdb_time duckdb_value_time(duckdb_result *result, idx_t col, idx_t row);
duckdb_timestamp duckdb_value_timestamp(duckdb_result *result, idx_t col, idx_t row);
duckdb_interval duckdb_value_interval(duckdb_result *result, idx_t col, idx_t row);
char *duckdb_value_varchar(duckdb_result *result, idx_t col, idx_t row);
char *duckdb_value_varchar_internal(duckdb_result *result, idx_t col, idx_t row);
duckdb_string duckdb_value_string_internal(duckdb_result *result, idx_t col, idx_t row);
duckdb_blob duckdb_value_blob(duckdb_result *result, idx_t col, idx_t row);
bool duckdb_value_is_null(duckdb_result *result, idx_t col, idx_t row);
Date/Time/Timestamp Helpers
duckdb_date_struct duckdb_from_date(duckdb_date date);
duckdb_date duckdb_to_date(duckdb_date_struct date);
duckdb_time_struct duckdb_from_time(duckdb_time time);
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);
Hugeint Helpers
double duckdb_hugeint_to_double(duckdb_hugeint val);
duckdb_hugeint duckdb_double_to_hugeint(double val);
duckdb_decimal duckdb_double_to_decimal(double val, uint8_t width, uint8_t scale);
Decimal Helpers
double duckdb_decimal_to_double(duckdb_decimal val);
Logical Type Interface
duckdb_logical_type duckdb_create_logical_type(duckdb_type type);
duckdb_logical_type duckdb_create_list_type(duckdb_logical_type type);
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_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_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_result_get_chunk
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.
returns
The resulting data chunk. Returns NULL if the chunk index is out of bounds.
duckdb_result_is_streaming
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.
returns
Whether or not the result object is of the type StreamQueryResult
duckdb_result_chunk_count
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
returns
Number of data chunks present in the result.
duckdb_value_boolean
Syntax
bool duckdb_value_boolean(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The boolean value at the specified location, or false if the value cannot be converted.
duckdb_value_int8
Syntax
int8_t duckdb_value_int8(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The int8_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_int16
Syntax
int16_t duckdb_value_int16(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The int16_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_int32
Syntax
int32_t duckdb_value_int32(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The int32_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_int64
Syntax
int64_t duckdb_value_int64(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The int64_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_hugeint
Syntax
duckdb_hugeint duckdb_value_hugeint(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_hugeint value at the specified location, or 0 if the value cannot be converted.
duckdb_value_decimal
Syntax
duckdb_decimal duckdb_value_decimal(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_decimal value at the specified location, or 0 if the value cannot be converted.
duckdb_value_uint8
Syntax
uint8_t duckdb_value_uint8(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The uint8_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_uint16
Syntax
uint16_t duckdb_value_uint16(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The uint16_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_uint32
Syntax
uint32_t duckdb_value_uint32(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The uint32_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_uint64
Syntax
uint64_t duckdb_value_uint64(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The uint64_t value at the specified location, or 0 if the value cannot be converted.
duckdb_value_float
Syntax
float duckdb_value_float(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The float value at the specified location, or 0 if the value cannot be converted.
duckdb_value_double
Syntax
double duckdb_value_double(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The double value at the specified location, or 0 if the value cannot be converted.
duckdb_value_date
Syntax
duckdb_date duckdb_value_date(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_date value at the specified location, or 0 if the value cannot be converted.
duckdb_value_time
Syntax
duckdb_time duckdb_value_time(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_time value at the specified location, or 0 if the value cannot be converted.
duckdb_value_timestamp
Syntax
duckdb_timestamp duckdb_value_timestamp(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_timestamp value at the specified location, or 0 if the value cannot be converted.
duckdb_value_interval
Syntax
duckdb_interval duckdb_value_interval(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_interval value at the specified location, or 0 if the value cannot be converted.
duckdb_value_varchar
Syntax
char *duckdb_value_varchar(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
DEPRECATED
use duckdb_value_string instead. This function does not work correctly if the string contains null bytes.
returns
The text value at the specified location as a null-terminated string, or nullptr if the value cannot be
converted. The result must be freed with duckdb_free.
duckdb_value_varchar_internal
Syntax
char *duckdb_value_varchar_internal(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
DEPRECATED
use duckdb_value_string_internal instead. This function does not work correctly if the string contains null bytes.
returns
The char* value at the specified location. ONLY works on VARCHAR columns and does not auto-cast. If the column is NOT a VARCHAR column this function will return NULL.
The result must NOT be freed.
duckdb_value_string_internal
Syntax
duckdb_string duckdb_value_string_internal(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
DEPRECATED
use duckdb_value_string_internal instead. This function does not work correctly if the string contains null bytes.
returns
The char* value at the specified location. ONLY works on VARCHAR columns and does not auto-cast. If the column is NOT a VARCHAR column this function will return NULL.
The result must NOT be freed.
duckdb_value_blob
Syntax
duckdb_blob duckdb_value_blob(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
The duckdb_blob value at the specified location. Returns a blob with blob.data set to nullptr if the
value cannot be converted. The resulting "blob.data" must be freed with duckdb_free.
duckdb_value_is_null
Syntax
bool duckdb_value_is_null(
duckdb_result *result,
idx_t col,
idx_t row
);
Parameters
returns
Returns true if the value at the specified index is NULL, and false otherwise.
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 a DUCKDB_TYPE_DATE column.
returns
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 a duckdb_date_struct.
returns
The duckdb_date element.
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 a DUCKDB_TYPE_TIME column.
returns
The duckdb_time_struct with the decomposed elements.
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 a duckdb_time_struct.
returns
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 a DUCKDB_TYPE_TIMESTAMP column.
returns
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 a duckdb_timestamp_struct.
returns
The duckdb_timestamp element.
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.
returns
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.
returns
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.
returns
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.
returns
The converted double element.
duckdb_create_logical_type
Creates a duckdb_logical_type from a standard primitive type.
The resulting type should be destroyed with duckdb_destroy_logical_type.
This should not be used with DUCKDB_TYPE_DECIMAL.
Syntax
duckdb_logical_type duckdb_create_logical_type(
duckdb_type type
);
Parameters
type
The primitive type to create.
returns
The logical type.
duckdb_create_list_type
Creates a list type from its child type.
The resulting type should 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 list type to create.
returns
The logical type.
duckdb_create_map_type
Creates a map type from its key type and value type.
The resulting type should 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
type
The key type and value type of map type to create.
returns
The logical type.
duckdb_create_union_type
Creates a UNION type from the passed types array
The resulting type should 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
types
The array of types that the union should consist of.
type_amount
The size of the types array.
returns
The logical type.
duckdb_create_decimal_type
Creates a duckdb_logical_type of type decimal 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 type
scale
The scale of the decimal type
returns
The logical type.
duckdb_get_type_id
Retrieves the type class of a duckdb_logical_type.
Syntax
duckdb_type duckdb_get_type_id(
duckdb_logical_type type
);
Parameters
type
The logical type object
returns
The 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
returns
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
returns
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
returns
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
returns
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
returns
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 object
index
The index in the dictionary
returns
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.
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 object
returns
The child type of the list type. Must be destroyed with duckdb_destroy_logical_type.
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
returns
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
returns
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
returns
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 object
index
The child index
returns
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 object
index
The child index
returns
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
returns
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 object
index
The child index
returns
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 object
index
The child index
returns
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.