Promotion of data types

Data types can be classified into groups of related data types. Within such groups, an order of precedence exists where 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 ordering. For example, the data type CHAR can be promoted to VARCHAR; INTEGER can be promoted to DOUBLE PRECISION; but CLOB is NOT promotable 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 11 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 11. Data Type Precedence Table
Data Type	Data Type Precedence List (in best-to-worst order)
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
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
BINARY	BINARY, VARBINARY, BLOB
VARBINARY	VARBINARY, BLOB
BLOB	BLOB
DATE	DATE
TIME	TIME
TIMESTAMP	TIMESTAMP
DATALINK	DATALINK
ROWID	ROWID
udt	same udt
Note: The lower case types above are defined as follows: decimal = DECIMAL(p,s) or NUMERIC(p,s) real = REAL or FLOAT(n) where n is a specification for single precision floating point double = DOUBLE, DOUBLE PRECISION, FLOAT or FLOAT(n) where n is a specification for double precision floating point udt = a user-defined type Shorter and longer form synonyms of the data types listed are considered to be the same as the synonym listed. Character and graphic strings are only compatible for Unicode data.

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