Considerations When Using the CREATE TABLE Statement

When creating tables for compatibility, be aware of the following compatibility considerations for NULL treatment, check constraints, referential integrity, default values, identify columns, computed columns, temporary tables, and table location.

NULL in Columns

For compatible treatment of NULL:

SQL Anywhere and Sybase IQ assume that columns can be null unless NOT NULL is stated in the column definition. You can change this behavior by setting the database option ALLOW_NULLS_BY_DEFAULT to the Transact-SQL compatible setting of OFF.
SQL Anywhere assumes that BIT columns only cannot be NULL.
Adaptive Server Enterprise assumes that columns cannot be null unless NULL is stated.

Check Constraints

Sybase IQ enforces check constraints on base, global temporary, and local temporary tables, and on user-defined data types. Users can log check integrity constraint violations and specify the number of violations that can occur before a LOAD statement rolls back.

Sybase IQ does not allow the creation of a check constraint that it cannot evaluate, such as those composed of user-defined functions, proxy tables, or non-Sybase IQ tables. Constraints that cannot be evaluated are detected the first time the table on which the check constraint is defined is used in a LOAD, INSERT, or UPDATE statement. Sybase IQ does not allow check constraints containing:

Subqueries
Expressions specifying a host language parameter, a SQL parameter, or a column as the target for a data value
Set functions
Invocations of nondeterministic functions or functions that modify data

Adaptive Server Enterprise and SQL Anywhere enforce CHECK constraints. SQL Anywhere allows subqueries in check constraints.

Sybase IQ supports user-defined data types that allow constraints to be encapsulated in the data type definition.

Referential Integrity Constraints

Sybase IQ enforces referential integrity as described in the System Administration Guide: Volume 1.

Actions for enforcing integrity are supported as follows:

SQL Anywhere supports all ANSI actions: SET NULL, CASCADE, DEFAULT, RESTRICT.
Adaptive Server Enterprise supports two of these actions: SET NULL, DEFAULT.

Note: You can achieve CASCADE in Adaptive Server Enterprise by using triggers instead of referential integrity.
Sybase IQ supports the RESTRICT action only.
Sybase IQ does not support NOT NULL FOREIGN KEY.
Sybase IQ has the restriction that a column cannot be both a candidate key and a foreign key at the same time.

Default Values in a Column

Default value support differs as follows:

Adaptive Server Enterprise and SQL Anywhere support specifying a default value for a column.
Only SQL Anywhere supports DEFAULT UTC TIMESTAMP.
Sybase IQ supports specifying a default value for a column, except for the special values DEFAULT UTC TIMESTAMP and DEFAULT CURRENT UTC TIMESTAMP. Sybase IQ also ignores settings for the DEFAULT_TIMESTAMP_INCREMENT database option.

Identity Columns

Identity column support differs as follows:

Sybase IQ supports IDENTITY or DEFAULT AUTOINCREMENT as a default value. Sybase IQ supports identity columns of any numeric type with any precision and scale 0, and the column can be NULL. Sybase IQ identity columns must be positive and are limited by the range of the data type. Sybase IQ supports a single identity column per table, and requires database option IDENTITY_INSERT set to a table name for explicit inserts and updates. To drop a table with an IDENTITY column, you cannot have IDENTITY_INSERT set to that table. The table can contain data when adding an identity column. Tables derived using SELECT INTO do not have Identity/Autoincrement columns. Sybase IQ views cannot contain IDENTITY/DEFAULT AUTOINCREMENT columns.
SQL Anywhere supports the AUTOINCREMENT default value. SQL Anywhere supports identity columns of any numeric type with any allowable scale and precision. The identity column value can be positive, negative, or zero, limited by the range of the data type. SQL Anywhere supports any number of identity columns per table, and does not require identity_insert for explicit inserts, drops, and updates. The table must be empty when adding identity columns. SQL Anywhere identity columns can be altered to be nonidentity columns, and vice versa. You can add or drop AUTOINCREMENT columns from SQL Anywhere views.
Adaptive Server Enterprise supports a single identity column per table. Adaptive Server Enterprise identity columns are restricted to only numeric data type scale 0, maximum precision 38. They must be positive, are limited by the range of the data type, and cannot be null. Adaptive Server Enterprise requires identity_insert for explicit inserts and drops, but not for updates to the identity column. The table can contain data when you add an identity column. Adaptive Server Enterprise users cannot explicitly set the next value chosen for an identity column. Adaptive Server Enterprise views cannot contain IDENTITY/AUTOINCREMENT columns. When using SELECT INTO under certain conditions, Adaptive Server Enterprise allows Identity/Autoincrement columns in the result table if they were in the table being selected from.

Computed Columns

Computed column support differs as follows:

SQL Anywhere supports computed columns that can be indexed.
Adaptive Server Enterprise and Sybase IQ do not.

Temporary Tables

You can create a temporary table by placing a pound sign (#) without an owner specification in front of the table name in a CREATE TABLE statement. These temporary tables are Sybase IQ-declared temporary tables and are available only in the current connection.

Locating Tables

Physical placement of a table is carried out differently in Adaptive Server Enterprise and Sybase IQ. Sybase IQ supports the ON segment-name clause, but segment-name refers to a Sybase IQ dbspace.