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

Microsoft™ SQL Server

Microsoft SQL Server provides IDENTITY columns to auto-generate numeric values:

• When creating a table, the IDENTITY keyword must be specified after the column data type:

  CREATE TABLE tab1 ( k INTEGER IDENTITY, c NVARCHAR(10) )

• You can specify a start value and an increment with IDENTITY(start,incr):

  CREATE TABLE tab1 ( k INTEGER IDENTITY(100,2), ...

• A new number is automatically created when inserting a new row:

  INSERT INTO tab1 ( c ) VALUES ( 'aaa' )

• To get the last generated number, Microsoft SQL SERVER provides the SCOPE_IDENTITY() function. The @@IDENTITY global T-SQL variable is not recommended, as it is scope-less.
• To put a specific value into an IDENTITY column, the SET IDENTITY_INSERT command must be used:

  SET IDENTITY_INSERT tab1 ON
  INSERT INTO tab1 ( k, c ) VALUES ( 100, 'aaa' )
  SET IDENTITY_INSERT tab1 OFF 

Informix SERIALs and SQL Server IDENTITY columns are quite similar; the main difference is that SQL Server does not allow you to use the zero value for the identity column when inserting a new row.

-- To create a sequence object:
CREATE SEQUENCE myseq START WITH 100 INCREMENT BY 1;

-- To get a new sequence value:
SELECT NEXT VALUE FOR myseq;

-- To find the current sequence value (last generated)
SELECT convert(bigint, current_value) FROM sys.sequences WHERE name = 'myseq';

-- To reset the sequence with a new start number:
ALTER SEQUENCE myseq START WITH 100;

Solution

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

1. native: uses IDENTITY columns.
2. trigseq: uses INSERT triggers with sequences (CREATE SEQUENCE).
3. 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}

The native IDENTITY-based solution is faster, but does not allow explicit serial value specification in insert statements; the other solutions are slower but allow explicit serial value specification in INSERT statements.

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().

1. Using the native serial emulation

In order to use the "native" emulation, make sure that the following FGLPROFILE entry is not defined (it is the default), or is set the entry to "native":

dbi.database.dbname.ifxemul.datatype.serial.emulation = "native"

In database creation scripts, all SERIAL[(n)] data types must be converted by hand to INTEGER IDENTITY[(n,1)] data types, while BIGSERIAL[(n)] data types must be converted by hand to BIGINT IDENTITY[(n,1)] data types.

Tables created from the BDL programs can use the SERIAL or BIGSERIAL data type: When a BDL program executes a CREATE [TEMP] TABLE with such column type, the database interface automatically converts to an identity column.

In BDL, the new generated SERIAL value is available from the sqlca.sqlerrd[2] variable. The database interface performs a SELECT SCOPE_IDENTITY(). However, since sqlca.sqlerrd[2] is defined as an INTEGER, it cannot hold values from BIGINT identity columns. When using a BIGINT IDENTITY column, retrieve the last generated serial with the SCOPE_IDENTITY() SQL function.

By default, you cannot specify the identity column in INSERT statements; All INSERT statements must be reviewed to remove the identity column from the list.

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

INSERT INTO tab (col2) VALUES (p_value)

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

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

Since 2.10.06, SELECT * FROM table INTO TEMP with original table having an IDENTITY column is supported: The database driver converts the Informix SELECT INTO TEMP to the following sequence of statements:

SELECT selection-items INTO #table FROM ... WHERE 1=2
SET IDENTITY_ INSERT #table ON
INSERT INTO #table ( column-list ) SELECT original select clauses
SET IDENTITY_ INSERT #table OFF

See also temporary tables.

2. Using the trigseq serial emulation (SQL Server 2012 and +)

In order to use the serial emulation based on triggers and sequences, make sure that all database users creating tables in program have permissions to create/drop sequences and triggers.

dbi.database.dbname.ifxemul.datatype.serial.emulation = "trigseq"

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

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 INSERT triggers. When using BIGSERIAL[(n)], the column is converted to a BIGINT.

3. Using the regtable serial emulation (SQL Server versions prior to 2012)

This solution is supported for SQL Server versions prior to 2012, if your server is SQL Server 2012 or +, consider using the "trigseq" emulation instead.

In order to use the serial emulation based on triggers and the SERIALREG table, make sure that all database users creating tables in program have permissions to create/drop triggers.

Then, prepare the database and create the SERIALREG table as follows:

CREATE TABLE serialreg (
    tablename VARCHAR(50) NOT NULL,
    lastserial BIGINT NOT NULL,
    PRIMARY KEY ( tablename )
)

Make sure that other users can read from the SERIALREG table (using database roles).

The SERIALREG table and columns have to be created with lower case names, since the SQL SERVER database is created with case sensitive names, because triggers are using this table in lower case.

dbi.database.dbname.ifxemul.datatype.serial.emulation = "regtable"

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

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 INSERT triggers. When using BIGSERIAL[(n)], the column is converted to a BIGINT.