Type conversion rules

Informix®

When using parameterized SQL statements (SQL with program variables), the Informix SQL engine supports various type conversions.

For example, it is possible to compare a VARCHAR column to an INTEGER program variable:

MAIN
    DEFINE v_int INTEGER
         , v_count INTEGER
    DATABASE test1
    CREATE TABLE tt1 ( col1 VARCHAR(10) )
    INSERT INTO tt1 VALUES ( '12345' )
    LET v_int = 12345
    SELECT COUNT(*) INTO v_count
       FROM tt1 WHERE col1 = v_int
    DISPLAY "count = ", v_count
END MAIN

PostgreSQL

PostgreSQL is more strict as Informix when comparing or assigning SQL column values to program variable, if the data types do not match.

With the above code example, PostgreSQL produces the following SQL error:

SQLSTATE: 42883
SQL message: operator does not exist: character varying = integer

A similar error is raised for date vs string and decimal vs string types.

Solution

A good coding convention is to always use a program variable type that corresponds to the database column type.

For a complete list of Informix / PostgreSQL data type correspondance, see Data type conversion table: Informix to PostgreSQL.

Tip: Check that the data stored in the database actually requires the current type of the column. For example, if a VARCHAR column contains (and should only contain) whole numbers, consider to modify the column type to SMALLINT, INTEGER or BIGINT.