Create_field Class Reference

Create_field is a description a field/column that may or may not exists in a table. More...

#include <create_field.h>

Inheritance diagram for Create_field:

Public Member Functions
size_t	max_display_width_in_codepoints () const
size_t	max_display_width_in_bytes () const
size_t	pack_length (bool dont_override=false) const
size_t	key_length () const
bool	explicit_display_width () const
void	set_max_display_width_from_create_field (const Create_field &create_field)
	Set the maximum display width based on another Create_field. More...
	Create_field ()
	Create_field (Field *field, Field *orig_field)
	Constructs a column definition from an object representing an actual column. More...
Create_field *	clone (MEM_ROOT *mem_root) const
bool	is_gcol () const
bool	is_virtual_gcol () const
void	init_for_tmp_table (enum_field_types sql_type_arg, uint32 max_length, uint32 decimals, bool is_nullable, bool is_unsigned, uint pack_length_override, const char *field_name="")
	Init for a tmp table field. More...
bool	init (THD *thd, const char *field_name, enum_field_types type, const char *length, const char *decimals, uint type_modifier, Item *default_value, Item *on_update_value, const LEX_CSTRING *comment, const char *change, List< String > *interval_list, const CHARSET_INFO *cs, bool has_explicit_collation, uint uint_geom_type, Value_generator *gcol_info, Value_generator *default_val_expr, std::optional< gis::srid_t > srid, dd::Column::enum_hidden_type hidden, bool is_array=false)
	Initialize a column definition object. More...
ha_storage_media	field_storage_type () const
column_format_type	column_format () const

Public Attributes
dd::Column::enum_hidden_type	hidden
const char *	field_name
const char *	change
	Name of column modified by ALTER TABLE's CHANGE/MODIFY COLUMN clauses, NULL for columns added. More...
const char *	after {nullptr}
LEX_CSTRING	comment
Item *	constant_default
	The declared default value, if any, otherwise NULL. More...
enum_field_types	sql_type
uint	decimals
uint	flags {0}
uchar	auto_flags {Field::NONE}
	Bitmap of flags indicating if field value should be auto-generated by default and/or on update, and in which way. More...
TYPELIB *	interval
List< String >	interval_list
const CHARSET_INFO *	charset
bool	is_explicit_collation
Field::geometry_type	geom_type
Field *	field
uint	offset
bool	is_nullable
	Indicate whether column is nullable, zerofill or unsigned. More...
bool	is_zerofill
bool	is_unsigned
bool	treat_bit_as_char
	Indicates that storage engine doesn't support optimized BIT field storage. More...
uint	pack_length_override {0}
	Row based replication code sometimes needs to create ENUM and SET fields with pack length which doesn't correspond to number of elements in interval TYPELIB. More...
Value_generator *	gcol_info {nullptr}
bool	stored_in_db
Value_generator *	m_default_val_expr {nullptr}
	Holds the expression to be used to generate default values. More...
std::optional< gis::srid_t >	m_srid
bool	is_array {false}
LEX_CSTRING	m_engine_attribute = EMPTY_CSTR
LEX_CSTRING	m_secondary_engine_attribute = EMPTY_CSTR

Private Attributes
size_t	m_max_display_width_in_codepoints {0}
	The maximum display width of this column. More...
bool	m_explicit_display_width {false}
	Whether or not the display width was given explicitly by the user. More...

Detailed Description

Create_field is a description a field/column that may or may not exists in a table.

The main usage of Create_field is to contain the description of a column given by the user (usually given with CREATE TABLE). It is also used to describe changes to be carried out on a column (usually given with ALTER TABLE ... CHANGE COLUMN).

Constructor & Destructor Documentation

Create_field() [1/2]

Create_field::Create_field ( )

inline

Create_field() [2/2]

Create_field::Create_field	(	Field *	old_field,
		Field *	orig_field
	)

Constructs a column definition from an object representing an actual column.

This is a reverse-engineering procedure that creates a column definition object as produced by the parser (Create_field) from a resolved column object (Field).

Parameters

old_field	The column object from which the column definition is constructed.
orig_field	Used for copying default values. This parameter may be NULL, but if present it is used for copying default values.

Default values are copied into an Item_string unless:

• The default value is a function.
• There is no default value.
• old_field is a BLOB column.
• old_field has its data pointer improperly initialized.

Member Function Documentation

clone()

Create_field * Create_field::clone ( MEM_ROOT *  mem_root ) const

inline

column_format()

column_format_type Create_field::column_format ( ) const

inline

explicit_display_width()

bool Create_field::explicit_display_width ( ) const

inline

Return values

true	if the maximum column length was given explicitly by the user.
false	if the user didn't specify any maximum length.

field_storage_type()

ha_storage_media Create_field::field_storage_type ( ) const

inline

init()

bool Create_field::init	(	THD *	thd,
		const char *	fld_name,
		enum_field_types	fld_type,
		const char *	display_width_in_codepoints,
		const char *	fld_decimals,
		uint	fld_type_modifier,
		Item *	fld_default_value,
		Item *	fld_on_update_value,
		const LEX_CSTRING *	fld_comment,
		const char *	fld_change,
		List< String > *	fld_interval_list,
		const CHARSET_INFO *	fld_charset,
		bool	has_explicit_collation,
		uint	fld_geom_type,
		Value_generator *	fld_gcol_info,
		Value_generator *	fld_default_val_expr,
		std::optional< gis::srid_t >	srid,
		dd::Column::enum_hidden_type	hidden,
		bool	is_array_arg = false
	)

Initialize a column definition object.

Column definition objects can be used to construct Field objects.

Parameters

thd	Session/Thread handle.
fld_name	Column name.
fld_type	Column type.
display_width_in_codepoints	The column display width, counted in number of code points.
fld_decimals	Number of digits to the right of the decimal point (if any.)
fld_type_modifier	Additional type information.
fld_default_value	Column default constant or datetime expression (if any.)
fld_on_update_value	The expression in the ON UPDATE clause.
fld_comment	Column comment.
fld_change	Column change.
fld_interval_list	Interval list (if any.)
fld_charset	Column charset.
has_explicit_collation	Column has an explicit COLLATE attribute.
fld_geom_type	Column geometry type (if any.)
fld_gcol_info	Generated column data
fld_default_val_expr	The expression for generating default values
srid	The SRID specification. This might be null (has_value() may return false).
hidden	Whether this column should be hidden or not.
is_array_arg	Whether the field is a typed array

Return values

false	on success.
true	on error.

init_for_tmp_table()

void Create_field::init_for_tmp_table	(	enum_field_types	sql_type_arg,
		uint32	length_arg,
		uint32	decimals_arg,
		bool	is_nullable_arg,
		bool	is_unsigned_arg,
		uint	pack_length_override_arg,
		const char *	fld_name = ""
	)

Init for a tmp table field.

To be extended if need be.

is_gcol()

bool Create_field::is_gcol ( ) const

inline

is_virtual_gcol()

bool Create_field::is_virtual_gcol ( ) const

inline

key_length()

size_t Create_field::key_length

(

)

const

Returns

the key length for this column.

max_display_width_in_bytes()

size_t Create_field::max_display_width_in_bytes

(

)

const

Returns

the maximum display width of this column, in number of bytes. For numeric types, temporal types, YEAR and BIT, this method returns the same as max_display_width_in_codepoints(). For character types (CHAR, VARCHAR, TEXT etc) the returned value depends on max_display_width_in_codepoints() and the character set of this column.

max_display_width_in_codepoints()

size_t Create_field::max_display_width_in_codepoints

(

)

const

Returns

the maximum display width of this column, in number of. code points. See m_max_display_width_in_codepoints for an explanation of "display width" and "code point".

pack_length()

size_t Create_field::pack_length

(

bool

dont_override = false

)

const

Returns

the pack length for this column, which is the number of bytes needed to store this column in memory. Note that blob returns a length variable + the size of a pointer to an external memory location where the actual data is stored. So LONGBLOB would return 4 bytes for the length variable + 8 bytes for the pointer to the data (12 bytes in total).

Parameters

dont_override

Don't use pack_length_override even if non-zero Used by multi-valued index, where pack_length and key_length aren't the same.

set_max_display_width_from_create_field()

void Create_field::set_max_display_width_from_create_field ( const Create_field &  create_field )

inline

Set the maximum display width based on another Create_field.

Member Data Documentation

after

const char* Create_field::after {nullptr}

auto_flags

uchar Create_field::auto_flags {Field::NONE}

Bitmap of flags indicating if field value should be auto-generated by default and/or on update, and in which way.

See also

Field::enum_auto_flags for possible options.

change

const char* Create_field::change

Name of column modified by ALTER TABLE's CHANGE/MODIFY COLUMN clauses, NULL for columns added.

charset

const CHARSET_INFO* Create_field::charset

comment

LEX_CSTRING Create_field::comment

constant_default

Item* Create_field::constant_default

The declared default value, if any, otherwise NULL.

Note that this member is NULL if the default is a function. If the column definition has a function declared as the default, the information is found in Create_field::auto_flags.

See also

Create_field::auto_flags

decimals

uint Create_field::decimals

field

Field* Create_field::field

field_name

const char* Create_field::field_name

flags

uint Create_field::flags {0}

gcol_info

Value_generator* Create_field::gcol_info {nullptr}

geom_type

Field::geometry_type Create_field::geom_type

hidden

dd::Column::enum_hidden_type Create_field::hidden

interval

TYPELIB* Create_field::interval

interval_list

List<String> Create_field::interval_list

is_array

bool Create_field::is_array {false}

is_explicit_collation

bool Create_field::is_explicit_collation

is_nullable

bool Create_field::is_nullable

Indicate whether column is nullable, zerofill or unsigned.

Initialized based on flags and other members at prepare_create_field()/ init_for_tmp_table() stage.

is_unsigned

bool Create_field::is_unsigned

is_zerofill

bool Create_field::is_zerofill

m_default_val_expr

Value_generator* Create_field::m_default_val_expr {nullptr}

Holds the expression to be used to generate default values.

m_engine_attribute

LEX_CSTRING Create_field::m_engine_attribute = EMPTY_CSTR

m_explicit_display_width

bool Create_field::m_explicit_display_width {false}

private

Whether or not the display width was given explicitly by the user.

m_max_display_width_in_codepoints

size_t Create_field::m_max_display_width_in_codepoints {0}

private

The maximum display width of this column.

The "display width" is the number of code points that is needed to print out the string representation of a value. It can be given by the user both explicitly and implicitly. If a user creates a table with the columns "a VARCHAR(3), b INT(3)", both columns are given an explicit display width of 3 code points. But if a user creates a table with the columns "a INT, b TINYINT UNSIGNED", the first column has an implicit display width of 11 (-2147483648 is the longest value for a signed int) and the second column has an implicit display width of 3 (255 is the longest value for an unsigned tinyint). This is related to storage size for some types (VARCHAR, BLOB etc), but not for all types (an INT is four bytes regardless of the display width).

A "code point" is basically a numeric value. For instance, ASCII compromises of 128 code points (0x00 to 0x7F), while unicode contains way more. In most cases a code point represents a single graphical unit (aka grapheme), but not always. For instance, É may consists of two code points where one is the letter E and the other one is the quotation mark above the letter.

m_secondary_engine_attribute

LEX_CSTRING Create_field::m_secondary_engine_attribute = EMPTY_CSTR

m_srid

std::optional<gis::srid_t> Create_field::m_srid

offset

uint Create_field::offset

pack_length_override

uint Create_field::pack_length_override {0}

Row based replication code sometimes needs to create ENUM and SET fields with pack length which doesn't correspond to number of elements in interval TYPELIB.

When this member is non-zero ENUM/SET field to be created will use its value as pack length instead of one calculated from number elements in its interval.

Initialized at prepare_create_field()/init_for_tmp_table() stage.

sql_type

enum_field_types Create_field::sql_type

stored_in_db

bool Create_field::stored_in_db

treat_bit_as_char

bool Create_field::treat_bit_as_char

Indicates that storage engine doesn't support optimized BIT field storage.

Note

We also use safe/non-optimized version of BIT field for special cases like virtual temporary tables.

Initialized at mysql_prepare_create_table()/sp_prepare_create_field()/ init_for_tmp_table() stage.

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The documentation for this class was generated from the following files:

• sql/create_field.h
• sql/create_field.cc