SERIAL and BIGSERIAL data types

Informix®

1. Create the table with a column using SERIAL, or BIGSERIAL.
2. To generate a new serial, no value or a zero value is specified in the INSERT statement:

   INSERT INTO tab1 ( c ) VALUES ( 'aa' )
   INSERT INTO tab1 ( k, c ) VALUES ( 0, 'aa' )

3. After INSERT, the new value of a SERIAL column is provided in sqlca.sqlerrd[2], while the new value of a BIGSERIAL value must be fetched with a SELECT dbinfo('bigserial') query.

Informix allows you to insert rows with a value different from zero for a serial column. Using an explicit value will automatically increment the internal serial counter, to avoid conflicts with future INSERT statements that are using a zero value:

SQL statement                                               Internal serial counter
------------------------------------------------------------------------------------------
CREATE TABLE tab ( pkey SERIAL, name VARCHAR(50) );                    0
INSERT INTO tab VALUES (  0, 'aaa' );                                  1
INSERT INTO tab VALUES ( 10, 'bbb' );                                 10
INSERT INTO tab VALUES (  0, 'ccc' );                                 11
DELETE FROM tab;                                                      11
INSERT INTO tab VALUES (  0, 'ddd' );                                 12

IBM® DB2®

CREATE TABLE tab ( k INTEGER GENERATED ALWAYS AS IDENTITY, name VARCHAR(50) )

To get the last generated IDENTITY value after an INSERT, DB2 provides the IDENTITY_VAL_LOCAL() function.

CREATE SEQUENCE sq1 START WITH 100

INSERT INTO table VALUES ( NEXTVAL FOR sq1, ... )

SELECT PREVVAL FOR sq1 ...

Solution

To emulate Informix serials with IBM DB2, you can use IDENTITY columns (1), or INSERT triggers using sequences (2). The first solution is faster, but does not allow explicit serial value specification in insert statements; the second solution is slower but allows explicit serial value specification.

dbi.database.dbname.ifxemul.datatype.serial.emulation = {"native"|"trigseq"}

• native: uses IDENTITY columns.
• trigseq: uses INSERT triggers with sequences.

The default emulation technique is "native".

dbi.database.dbname.ifxemul.datatype.serial = {true|false}
dbi.database.dbname.ifxemul.datatype.serial8 = {true|false}
dbi.database.dbname.ifxemul.datatype.bigserial = {true|false}

Disabling automatic serial retrieval for sqlca.sqlerrd[2]

For Informix compatibility, when the SERIAL type emulation is active, the ODI drivers automatically execute another SQL query (or do a DB client API call when possible) after each INSERT statement, to get the last generated serial, and fill the sqlca.sqlerrd[2] register. This results in some overhead that can be avoided, if the sqlca.sqlerrd[2] register is not used by the program.

When serial emulation is required (to create temp tables with a serial column during program execution), and the sqlca.sqlerrd[2] register does not need to be filled, (typically because you use your own method to retrieve the last generated serial), you can set the ifxemul.datatype.serial.sqlerrd2 FGLPROFILE entry to false. This will avoid the automatic retrieval of last serial value to fill sqlca.sqlerrd[2]:

dbi.database.dbname.ifxemul.datatype.serial.sqlerrd2 = false

dbi.database.dbname.ifxemul.datatype.serial = false

See also db_get_last_serial().

Using the native serial emulation

In database creation scripts, all SERIAL[(n)] data types must be converted by hand to:

INTEGER GENERATED ALWAYS AS IDENTITY[( START WITH n, INCREMENT BY 1)]

BIGINT GENERATED ALWAYS AS IDENTITY[( START WITH n, INCREMENT BY 1)]

Tables created from the BDL programs can use the SERIAL data type: When a BDL program executes a CREATE [TEMP] TABLE with a SERIAL column, the database interface automatically converts the SERIAL[(n)] data type to an IDENTITY specification.

In BDL, the new generated SERIAL value is available from the sqlca.sqlerrd[2] variable. The database interface performs a call to the IDENTITY_VAL_LOCAL() function. However, sqlca.sqlerrd[2] is defined as an INTEGER, it cannot hold values from BIGINT identity columns. If you are using BIGINT IDENTITY columns, you must use the IDENTITY_VAL_LOCAL() function.

INSERT INTO tab (col1,col2) VALUES (0, p_value)

INSERT INTO tab (col2) VALUES (p_value)

Static SQL INSERT using records defined from the schema file must also be reviewed:

DEFINE rec LIKE tab.*
INSERT INTO tab VALUES ( rec.* ) -- will use the serial column 

INSERT INTO tab VALUES rec.* -- without parentheses, serial column is removed

Using the trigseq serial emulation

In database creation scripts, all SERIAL[(n)] data types must be converted to INTEGER data types, SERIAL8/BIGSERIAL must be converted to BIGINT, and you must create a sequence and a trigger for each table using a SERIAL.

To know how to write those triggers, you can create a small Genero program that creates a table with a SERIAL column. Set the FGLSQLDEBUG environment variable and run the program. The debug output will show you the native SQL commands to create the sequence and the trigger.

Tables created from the BDL programs can use the SERIAL data type: When a BDL program executes a CREATE [TEMP] TABLE with a SERIAL column, the database interface automatically converts the SERIAL[(n)] data type to INTEGER and creates the sequence and the INSERT trigger.

INSERT INTO tab VALUES (NULL,p_value)

INSERT INTO tab (col2) VALUES (p_value)