SERIAL 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:

CREATE TABLE tab ( k SERIAL); -- internal counter = 0
INSERT INTO tab VALUES ( 0 ); -- internal counter = 1
INSERT INTO tab VALUES ( 10 ); -- internal counter = 10
INSERT INTO tab VALUES ( 0 ); -- internal counter = 11
DELETE FROM tab; -- internal counter = 11
INSERT INTO tab VALUES ( 0 ); -- internal counter = 12

ORACLE

Details about Oracle sequences:

• Sequences are totally detached from tables.
• The purpose of sequences is to provide unique integer numbers.
• Sequences are identified by a sequence name.
• To create a sequence, you must use the CREATE SEQUENCE statement. Once a sequence is created, it is permanent (like a table).
• To get a new sequence value, you must use the nextval keyword, preceded by the name of the sequence. The seqname.nextval expression can be used in INSERT statements:

  INSERT INTO tab1 VALUES ( tab1_seq.nextval, ... )

• To get the last generated number, Oracle provides the currval keyword:

  SELECT seqname.currval FROM DUAL

• In order to improve performance, Oracle can handle a set of sequences in the cache (See CREATE SEQUENCE syntax in the Oracle documentation).

Solution

The SERIAL data type can be emulated with sequences used in INSERT triggers or with the DEFAULT ON NULL clause.

dbi.database.dbname.ifxemul.datatype.serial.emulation = {"native"|"native2"|"regtable"}

• native: uses insert triggers with sequences.
• native2: uses DEFAULT ON NULL column clause with sequences.
• regtable: uses insert triggers with the SERIALREG table.

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}

Notes common to all serial emulation modes

When a BDL program executes a CREATE [TEMP] TABLE with a SERIAL column, the Oracle interface automatically creates the additional SQL objects (column clauses, sequences or triggers) to generate numbers when an INSERT statement is performed.

Users executing programs which create tables with SERIAL columns must have the CONNECT and RESOURCE roles assigned to create triggers and sequences.

SERIAL[(n)] data types are converted to NUMBER(10,0), while BIGSERIAL[(n)] is replaced by NUMBER(20,0).

For SERIAL types, the SQLCA.SQLERRD[2] register is filled as expected with the last generated serial value. However, since SQLCA.SQLERRD[2] is defined as an INTEGER, it cannot hold values from BIGSERIAL (NUMBER(20,0)) auto-incremented columns. If you are using BIGSERIAL columns, you must the fetch the sequence pseudo-column CURR_VAL or fetch the LASTSERIAL column from the SERIALREG table, if used.

INSERT INTO tab ( col1, col2 ) VALUES ( NULL, 'data' )

INSERT INTO tab (col2) VALUES ('data')

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

INSERT INTO tab (col2) VALUES (p_value)

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

When using the Static SQL INSERT or UPDATE syntax using record.* without parentheses, make sure that your database schema files contain information about serials. This information can be lost when extracting the schema from an Oracle database. See Database Schema for more details about the serial flag in column type encoding (data type code must be 6).

If the "native" or "regtable" emulation is used, inserting rows with Oracle tools like SQL*Plus or SQL*Loader will execute the INSERT triggers. When loading big tables, you can disable triggers with ALTER TRIGGER [ENABLE | DISABLE] (see Oracle documentation for more details). After reactivation of the serial triggers, the SERIAL sequences must be re-initialized (use serialpkg.create_sequence('tab','col')) or re-execute the PL/SQL script containing the sequence and trigger creation.

Using the native serial emulation

Each table having a SERIAL column needs an INSERT TRIGGER and a SEQUENCE dedicated to SERIAL generation.

To know how to write those sequences and 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.

For temporary tables, the trigger and the sequence are dropped automatically after a "DROP TABLE temptab" or when the program disconnects from the database.

Using the native2 serial emulation

CREATE TABLE t1 ( mykey SERIAL(100), .... )

CREATE SEQUENCE t1_srl INCREMENT BY 1 START WITH 100
CREATE TABLE t1 (mykey NUMBER(10,0) DEFAULT ON NULL t1_srl.nextval , ...

For temporary tables, the sequence is dropped automatically after a "DROP TABLE temptab" or when the program disconnects from the database.

Using the regtable serial emulation

Each table having a SERIAL column needs an INSERT TRIGGER which uses the SERIALREG table dedicated to SERIAL registration.

First, you must prepare the database and create the SERIALREG table as follows:

CREATE TABLE serialreg (
    tablename VARCHAR2(50) NOT NULL,
    lastserial NUMBER(20,0) NOT NULL,
    PRIMARY KEY ( tablename )
)

In database creation scripts, all SERIAL[(n)] data types must be converted to INTEGER data types and you must create one trigger for each table. SERIAL8/BIGSERIAL columns must be converted to NUMBER(20,0). 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 trigger creation command.

The serial production is based on the SERIALREG table which registers the last generated number for each table. If you delete rows of this table, sequences will restart at start values and you might get duplicated values.

For temporary tables, the trigger is dropped automatically after a "DROP TABLE temptab" or when the program disconnects from the database.