DATE and DATETIME data types

Informix®

Informix provides two data types to store date and time information:

DATE = for year, month and day storage.
DATETIME = for year to fraction (1-5) storage.

The DATE type is stored as an INTEGER with the number of days since 1899/12/31.

The DATETIME type can be defined with various time units, by specifying a start and end qualifier. For example, you can define a datetime to store an hour-to-second time value with DATETIME HOUR TO SECOND.

The values of Informix DATETIME can be represented with a character string literal, or as DATETIME() literals:

'2017-12-24 15:45:12.345'  -- a DATETIME YEAR TO FRACTION(3)
'15:45'   -- a DATETIME HOUR TO MINUTE
DATETIME(2017-12-24 12:45) YEAR TO MINUTE
DATETIME(12:45:56.333) HOUR TO FRACTION(3)

Informix is able to convert quoted strings to DATE / DATETIME data, if the string contains matching environment parameters. The string to date conversion rules for DATE is defined by the DBDATE environment variable. The string to datetime format for DATETIME is defined by the GL_DATETIME environment variable.

Note: Within Genero programs, the string representation for DATETIME values is always ISO (YYYY-MM-DD hh:mm:ss.fffff)

Informix supports date arithmetic on DATE and DATETIME values. The result of an arithmetic expression involving dates/times is an INTEGER number of days when only DATE values are used, and an INTERVAL value if a DATETIME is used in the expression.

Informix automatically converts an INTEGER to a DATE when the integer is used to set a value of a date column.

SQLite

SQLite 3 does not have a native type for date/time storage, but you can use data/time type names and functions based on the string representation of dates and times. The date/time values are stored in the TEXT native type.

The date/time functions of SQLite are based on standard DATE (YYYY-MM-DD), TIME (hh:mm:ss) and TIMESTAMP (YYYY-MM-DD hh:mm:ss) concepts.

For maximum flexibility with other RDBMS SQL languages, SQLite allows you to define table columns with your own type names. You can for example use the SMALLDATETIME, SMALLTIME, TIME(N), DATETIME(N) type names.

Solution

All Informix - BDL date/time types can be stored in SQLite date/time columns.

Since SQLite allows various data type names, the date/time type conversion rules define specific type names such as SMALLTIME, TINYDATETIME, to map original Informix date/time types. This allows the SQLite ODI driver and the fgldbsch tool detect the exact date/time type of a column. When a CREATE TABLE statement in a BDL program uses DATETIME HOUR TO MINUTE, it is mapped to a SMALLTIME by the ODI driver, and when extracting the database schema, fgldbsch can recognized SMALLTIME as a BDL / Informix DATETIME HOUR TO MINUTE column.

The storage format must follow the ISO date/time formatting style (YYYY-MM-DD hh:mm:ss.fffff). Depending on the BDL date/time precision, some parts will be omitted. For example a DATETIME HOUR TO MINUTE is stored as hh:mm (see conversion table below for more details).

Use the following conversion rules to map Informix date/time types to SQLite date/time (pseudo) types:

Table 1. Informix data types and SQLite equivalents
Informix data type	SQLite (pseudo data type)	Storage format
`DATE`	`DATE`	`YYYY-MM-DD`
`DATETIME HOUR TO HOUR`	`SMALLTIME`	`hh:00`
`DATETIME HOUR TO MINUTE`	`SMALLTIME`	`hh:mm`
`DATETIME HOUR TO SECOND`	`TIME`	`hh:mm:ss`
`DATETIME HOUR TO FRACTION(n)`	`TIME(n)`	`hh:mm:ss.fffff`
`DATETIME MINUTE TO MINUTE`	`SMALLTIME`	`00:mm`
`DATETIME MINUTE TO SECOND`	`TIME`	`00:mm:ss`
`DATETIME MINUTE TO FRACTION(n)`	`TIME(n)`	`00:mm:ss.fffff`
`DATETIME SECOND TO SECOND`	`TIME`	`00:00:ss`
`DATETIME SECOND TO FRACTION(n)`	`TIME(n)`	`00:00:ss.fffff`
`DATETIME FRACTION TO FRACTION(n)`	`TIME(n)`	`00:00:00.fffff`
`DATETIME YEAR TO YEAR`	`TINYDATETIME`	`YYYY-01-01`
`DATETIME YEAR TO MONTH`	`TINYDATETIME`	`YYYY-MM-01`
`DATETIME YEAR TO DAY`	`TINYDATETIME`	`YYYY-MM-DD`
`DATETIME YEAR TO HOUR`	`SMALLDATETIME`	`YYYY-MM-DD hh:00`
`DATETIME YEAR TO MINUTE`	`SMALLDATETIME`	`YYYY-MM-DD hh:mm`
`DATETIME YEAR TO SECOND`	`DATETIME`	`YYYY-MM-DD hh:mm:ss`
`DATETIME YEAR TO FRACTION(n)`	`DATETIME(n)`	`YYYY-MM-DD hh:mm:ss.fffff`
`DATETIME MONTH TO MONTH`	`TINYDATETIME`	`1900-MM-01`
`DATETIME MONTH TO DAY`	`TINYDATETIME`	`1900-MM-DD`
`DATETIME MONTH TO HOUR`	`SMALLDATETIME`	`1900-MM-DD hh:00`
`DATETIME MONTH TO MINUTE`	`SMALLDATETIME`	`1900-MM-DD hh:mm`
`DATETIME MONTH TO SECOND`	`DATETIME`	`1900-MM-DD hh:mm:ss`
`DATETIME MONTH TO FRACTION(n)`	`DATETIME(n)`	`1900-MM-DD hh:mm:ss.fffff`
`DATETIME DAY TO DAY`	`TINYDATETIME`	`1900-01-DD`
`DATETIME DAY TO HOUR`	`SMALLDATETIME`	`1900-01-DD hh:00`
`DATETIME DAY TO MINUTE`	`SMALLDATETIME`	`1900-01-DD hh:mm`
`DATETIME DAY TO SECOND`	`DATETIME`	`1900-01-DD hh:mm:ss`
`DATETIME DAY TO FRACTION(n)`	`DATETIME(n)`	`1900-01-DD hh:mm:ss.fffff`

The DATE and DATETIME types translation can be controlled with the following FGLPROFILE entries:

dbi.database.dsname.ifxemul.datatype.date = { true | false }
dbi.database.dsname.ifxemul.datatype.datetime = { true | false }

For more details see IBM Informix emulation parameters in FGLPROFILE.

In SQL statements, CURRENT expressions are converted to SQLite strftime('%Y-%m-%d %H:%M:%S','now'). The SQLite 'now' option returns the current date/time in UTC, while the FGL runtime system CURRENT instruction returns the current local time. Both values can be different. Always consider using SQL parameters with program variables assigned by the CURRENT instruction of Genero BDL, instead of using CURRENT instructions in SQL statements.