Gbase 8C system table PG_ attribute

pg_attribute System tables store information about table fields .

name	type	quote	describe
attrelid	oid	pg_class.oid	The table to which the column belongs
attname	name		Name
atttypid	oid	pg_type.oid	The data type of the column
attstattarget	int4		attstattarget Control by ANALYZE The level of detail of the statistics collected for this column .0 Value means that no statistics will be collected . A negative value indicates that the default target of the system is directly used . The exact meaning of a positive value depends on the data type . For scalar data types ,attstattarget Is to collect “ The most common value ” Target number of , It is also the target number of the histogram container to be created .
attlen	int2		Of this column type pg_type.typlen a copy
attnum	int2		Number of columns . Generally, it is listed from 1 Start numbering up . System column （ Such as oid） You have （ arbitrarily ） Negative number .
attndims	int4		If the column is an array type , Here is its dimension ; Otherwise 0.（ At present, the number of dimensions of an array is not mandatory , Therefore, any non-zero value can effectively indicate “ This is an array ”.）
attcacheoff	int4		In storage, it is always -1, But when it is loaded into a row descriptor in memory , Here it may be updated to the offset of the attribute in the row
atttypmod	int4		atttypmod Records the type related data provided when the table is created （ For example, one varchar The maximum length of the column ）. It will be passed to the type related input function and length constraint function . For those who don't need atttypmod The type of , This value is always -1.
attbyval	bool		Of this column type pg_type.typbyval A copy of
attstorage	char		Usually of this column type pg_type.typstorage A copy of . For can TOAST Data type of , This can be modified after the column is created to control the storage policy .
attalign	char		Of this column type pg_type.typalign A copy of
attnotnull	bool		This represents a non empty constraint .
atthasdef	bool		This column has a default value , In this case, in pg_attrdef There will be a corresponding entry in the directory to really record the default value .
attidentity	char		If it is zero bytes (''), Is not an identification column . otherwise ,a = Always generated , d = Default generated .
attisdropped	bool		The column has been deleted and is no longer valid . A deleted column still physically exists in the table , But it will be ignored by the analyzer and therefore cannot pass SQL visit .
attislocal	bool		This column is defined locally by the relationship . Note that a column can be both locally defined and inherited .
attinhcount	int4		The number of the direct ancestor of this column . A column with non-zero numbered ancestors cannot be deleted or renamed .
attcollation	oid	pg_collation.oid	The sorting rules defined for this column , If the column is not a sortable data type, then 0.
attacl	aclitem[]		Column level access
attoptions	text[]		Attribute level options , With “keyword=value” String of form
attfdwoptions	text[]		Attribute level external data wrapper options , With “keyword=value” String of form