Files > SQLI_PRIMARY_KEY

name

SQLI_PRIMARY_KEY

number

1.5218

location

^DMSQ("P",

description

A chosen set of columns which uniquely identify a table. In the relational model (as in set theory) the columns of a primary key are not ordered. In SQLI they must be, in order to map to the quasi- hierarchical model of M globals. FileMan subfiles (multiples) have a primary key element for each parent plus one for the subfile. Each contains a pointer to its primary key table element (SQLI_TABLE-ELEMENT), a sequence and a column in the local base table (SQL_COLUMN).

Fields

#	Name	Location	Type	Details	Index	Description
.01	p tbl element(+)	0;1	POINTER	1.5216	B	IEN of table element in SQLI_TABLE_ELEMENT
1	p column(+)	0;2	POINTER	1.5217	D	IEN of column in SQLI_COLUMN corresponding to this primary key
2	p sequence(+)	0;3	NUMERIC			Sequence number of primary key
3	p start at	0;4	FREE TEXT			Initial value of key before a $ORDER loop
4	p end if	1;E1,245	FREE TEXT			M expression in key value, {K}, which, if false, ends the $ORDER loop
5	p row count	0;5	NUMERIC			Estimated number of rows per record set at this level
6	p preselect	2;E1,245	FREE TEXT			Code to be executed before selecting this key, before optimization.
7	p key format	0;6	POINTER	1.5213		Key formats map internal storage values to their value when used as keys. In general, information is lost in the process; they can't be converted back. This means data must be converted to key format before it can be compared to such a key.