Constraints help to ensure that the data entered into a table is correct,
and provide information to SAP Sybase IQ that boosts
performance.
The CREATE TABLE statement and ALTER
TABLE statement can specify many different attributes
for a table. Along with the basic table structure (number, name
and data type of columns, name and location of the table), you can specify
other features that allow control over data integrity.
Warning! Altering or creating tables might adversely interfere with other users of the
database. For large tables, ALTER TABLE or
CREATE TABLE can be a time-consuming
operation. CREATE TABLE processing delays
execution of other processes until the statement completes. Although you can execute
ALTER TABLE statements while other
connections are active, you cannot execute them if any other connection is using the
table to be altered. During ALTER TABLE, no other
requests referencing the table being altered are allowed while the statement is
being processed.