LOAD and UNLOAD instructions

The LOAD and UNLOAD instructions can produce different data formats depending on the database server type.

The Genero BDL runtime system implements the LOAD and UNLOAD instructions, by using and INSERT (for LOAD) or SELECT (for UNLOAD) SQL commands.

To handle the values to be used in the INSERT statements for LOAD, or to hold the data fetched from the SELECT for UNLOAD, the runtime system needs to allocate data buffers dynamically. This operation requires the description of the column types in order to work.

As each database defines its native set of SQL data types, you must pay attention to the BDL type that results from the native database column type.

Depending on the native SQL data type, data formatting may be different from Informix® SQL / Genero BDL.

For example, when using Oracle DB, if the table contains a DATE column, the LOAD and UNLOAD instruction will use the date/time format YYYY-MM-DD hh:mm:ss. Since the native Oracle DATE type can be used to store both Informix / BDL DATE or DATETIME YEAR TO SECOND values, and as LOAD / UNLOAD need to make date/time to string conversions when reading from or writing to unload files, it impossible to distinguish the Informix/BDL native date type formats.

When using LOAD/UNLOAD, if the target database server provides the exact equivalent date types as the native Informix/BDL DATE, the date values will use the DBDATE format setting.

Table 1. Database server support of LOAD and UNLOAD
Database Server Type	LOAD/UNLOAD support
IBM® Informix	Yes, native SQL feature
Microsoft™ SQL Server	Yes, with some limitations
Oracle® MySQL / MariadDB	Yes, see details
Oracle Database Server	Yes, with some limitations
PostgreSQL	Yes, see details
SAP HANA®	Yes, see details
SQLite	Yes, see details
Dameng®	Yes, see details

To export table rows from a database brand that is different from the target database, format the data, to prepare for the native column types of the destination database.

For example, to unload from Informix and load into Oracle DB, format date/time columns:

FUNCTION ifx_type_to_expr_for_oracle(tn STRING) RETURNS STRING
    CASE
    WHEN tn == "DATE"                              RETURN "TO_CHAR(%1,'%%Y-%%m-%%d 00:00:00')"
    WHEN tn == "DATETIME YEAR TO YEAR"             RETURN "%1||'-01-01 00:00:00'"
    WHEN tn == "DATETIME YEAR TO MONTH"            RETURN "%1||'-01 00:00:00'"
    WHEN tn == "DATETIME YEAR TO DAY"              RETURN "%1||' 00:00:00'"
    WHEN tn == "DATETIME YEAR TO MINUTE"           RETURN "%1||':00'"
    WHEN tn == "DATETIME HOUR TO SECOND"           RETURN "'1900-01-01 '||%1"
    WHEN tn == "DATETIME HOUR TO MINUTE"           RETURN "'1900-01-01 '||%1||':00'"
    WHEN tn MATCHES "DATETIME HOUR TO FRACTION*"   RETURN "'1900-01-01 '||%1"
    WHEN tn MATCHES "INTERVAL YEAR* TO YEAR"       RETURN "%1-00"
    WHEN tn MATCHES "INTERVAL YEAR* TO MONTH"      RETURN "%1"
    WHEN tn MATCHES "INTERVAL HOUR* TO MINUTE"     RETURN "'0 '||%1||':00'"
    WHEN tn MATCHES "INTERVAL HOUR* TO SECOND"     RETURN "'0 '||%1"
    WHEN tn MATCHES "INTERVAL HOUR* TO FRACTION*"  RETURN "'0 '||%1"
    OTHERWISE                                      RETURN "%1"
    END CASE
END FUNCTION

FUNCTION build_select(tn STRING) RETURNS STRING
    DEFINE x INTEGER
    DEFINE sqlcmd base.StringBuffer
    DEFINE curs base.SqlHandle
    LET curs = base.SqlHandle.create()
    CALL curs.prepare("SELECT * FROM "||tn)
    CALL curs.open()
    LET sqlcmd = base.StringBuffer.create()
    CALL sqlcmd.append("SELECT ")
    FOR x=1 TO curs.getResultCount()
        IF x>1 THEN
            CALL sqlcmd.append( ", " )
        END IF
        CALL sqlcmd.append(
             SFMT( ifx_type_to_expr(curs.getResultType(x)),
                   curs.getResultName(x) )
             )
    END FOR
    CALL sqlcmd.append( " FROM " || tn )
    RETURN sqlcmd.toString()
END FUNCTION