Data types can be classified into groups of related data types. Within such groups, a precedence order exists where one data type is considered to precede another data type. This precedence is used to allow the promotion of one data type to a data type later in the precedence ordering. For example, the data type CHAR can be promoted to VARCHAR; INTEGER can be promoted to DOUBLE PRECISION; but CLOB is NOT promotable to VARCHAR.
Promotion of data types is used when:
Table 5 shows the precedence list (in order) for each data type and
can be used to determine the data types to which a given data type can be
promoted. The table shows that the best choice is always the same data
type instead of choosing to promote to another data type.
Table 5. Data Type Precedence Table
| Data Type | Data Type Precedence List (in best-to-worst order) | ||
|---|---|---|---|
| CHAR | CHAR, VARCHAR, LONG VARCHAR, CLOB | ||
| VARCHAR | VARCHAR, LONG VARCHAR, CLOB | ||
| LONG VARCHAR | LONG VARCHAR, CLOB | ||
| GRAPHIC | GRAPHIC, VARGRAPHIC, LONG VARGRAPHIC, DBCLOB | ||
| VARGRAPHIC | VARGRAPHIC, LONG VARGRAPHIC, DBCLOB | ||
| LONG VARGRAPHIC | LONG VARGRAPHIC, DBCLOB | ||
| BLOB | BLOB | ||
| CLOB | CLOB | ||
| DBCLOB | DBCLOB | ||
| SMALLINT | SMALLINT, INTEGER, BIGINT, decimal, real, double | ||
| INTEGER | INTEGER, BIGINT, decimal, real, double | ||
| BIGINT | BIGINT, decimal, real, double | ||
| decimal | decimal, real, double | ||
| real | real, double | ||
| double | double | ||
| DATE | DATE | ||
| TIME | TIME | ||
| TIMESTAMP | TIMESTAMP | ||
| DATALINK | DATALINK | ||
| udt | udt (same name) | ||
| REF(T) | REF(S) (provided that S is a supertype of T) | ||
The lower case types above are defined as follows:
Shorter and longer form synonyms of the data types listed are considered to be the same as the synonym listed. | |||