SQL/MX 2.x Reference Manual (H06.04+)

SQL/MX Statements

HP NonStop SQL/MX Reference Manual—540440-003

2-17

Syntax Description of ALTER TABLE

If you specify CASCADE and referential constraints are dependent on the

constraint, those dependent constraints are dropped in addition to the specified

constraint being dropped.

If you drop a constraint, NonStop SQL/MX drops its dependent index if SQL/MX

originally created the same index. If the constraint uses an existing index, the index

is not dropped.

The default is RESTRICT.

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 6-12.

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

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 unless the column is part

of the PRIMARY KEY.

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. All columns defined as unique must be specified as

NOT NULL.

A UNIQUE constraint is enforced with a unique index. If there is already a unique

index on column-list, NonStop SQL/MX uses this index; if not, the system

creates a unique index.

PRIMARY KEY [ASC[ENDING] | DESC[ENDING]] DROPPABLE]

PRIMARY KEY key-column-list

is a column or table constraint (respectively) that specifies a column or set of

columns as the primary key for the table. key-column-list cannot include more

than one occurrence of the same column. In addition, the set of columns you