Promotion of Data Types

Data types can be classified into groups of related data types. Within such groups, an order of precedence exists in which one data type is considered to precede another data type. This precedence enables the database manager to support the promotion of one data type to another data type that appears later in the precedence order. For example, the database manager can promote the data type CHAR to VARCHAR and the data type INTEGER to DOUBLE PRECISION; however, the database manager cannot promote a CLOB to a VARCHAR.

The database manager considers the promotion of data types when:

• Performing function resolution (see Function Resolution)
• Casting distinct types (see Casting Between Data Types)
• Assigning distinct types to built-in data types (see Distinct Type Assignments)

For each data type, Table 7 shows the precedence list (in order) that the database manager uses to determine the data types to which each data type can be promoted. The table indicates that the best choice is the same data type and not promotion to another data type. Note that the table also shows data types that are considered equivalent during the promotion process. For example, CHARACTER and GRAPHIC are considered to be equivalent data types.

Table 7. Precedence of Data Types

Data Type *	Data Type Precedence List (in best-to-worst order)
CHAR or GRAPHIC	CHAR or GRAPHIC, VARCHAR or VARGRAPHIC, CLOB or DBCLOB
VARCHAR or VARGRAPHIC	VARCHAR or VARGRAPHIC, CLOB or DBCLOB
CLOB or DBCLOB	CLOB or DBCLOB
BLOB	BLOB
SMALLINT	SMALLINT, INTEGER, BIGINT, DECIMAL or NUMERIC, REAL, DOUBLE
INTEGER	INTEGER, BIGINT, DECIMAL or NUMERIC, REAL, DOUBLE
BIGINT	BIGINT, DECIMAL or NUMERIC, REAL, DOUBLE
DECIMAL or NUMERIC	DECIMAL or NUMERIC, REAL, DOUBLE
REAL	REAL, DOUBLE
DOUBLE	DOUBLE
DATE	DATE
TIME	TIME
TIMESTAMP	TIMESTAMP
DATALINK	DATALINK
A distinct type	The same distinct type
Notes: * Other synonyms for the listed data types are considered to be the same as the synonym listed.