SQL/MX 3.2 Reference Manual (H06.25+, J06.14+)

SQL/MX Statements
HP NonStop SQL/MX Release 3.2 Reference Manual—691117-001
2-16
Syntax Description of ALTER TABLE
[CONSTRAINT constraint] column-constraint
specifies a name constraint and constraint definition for a column
constraint. See Database Object Names on page 6-13.
ADD [CONSTRAINT constraint] table-constraint
adds a constraint to the table and optionally specifies constraint as the name
for the constraint. The new constraint must be consistent with any data already
present in the table.
CONSTRAINT constraint
specifies a name for the column or table constraint. constraint must have
the same catalog and schema as table and must be unique among constraint
names in that schema. If you omit the catalog portion or the catalog and
schema portions of the name you specify in constraint, NonStop SQL/MX
expands the name by using the catalog and schema for table. See Database
Object Names on page 6-13.
If you do not specify a constraint name, NonStop SQL/MX constructs an SQL
identifier as the name for the constraint in the catalog and schema for table.
The identifier consists of the fully qualified table name concatenated with a
system-generated unique identifier. For example, a constraint on table A.B.C
might be assigned a name such as A.B.C_971..._01... . .
UNIQUE
or
UNIQUE column-list
is a column or table constraint (respectively) that specifies that the column or
set of columns cannot contain more than one occurrence of the same value or
set of values. If you omit UNIQUE, duplicate values are allowed.
column-list cannot include more than one occurrence of the same column.
In addition, the set of columns you specify on a UNIQUE constraint cannot
match the set of columns on any other UNIQUE constraint for the table or on
the PRIMARY KEY constraint for the table. Columns you define as unique
must be specified as NOT NULL.
A UNIQUE constraint is enforced with a unique index. If there is already a
user-defined unique index on column-list, NonStop SQL/MX uses this
index; if not, the system creates a unique index.
The maximum combined length of the columns for a UNIQUE constraint is
2010 bytes for 4K blocks and 2048 bytes for 32K blocks.