According to the Query/400 Use manual (SC41-5210), a seven-byte character string used with the DATE function is considered to be a Julian date in the format ccyyddd. To convert a Julian date in the format yyddd or cyyddd to a date data type date, you can use an expression such as the following:
DATE(SUBSTR(DIGITS(1900000 + JULDAT), 2, 7))
Field JULDAT must be defined as numeric for the expression to work.
To demonstrate what actually happens, let’s break down the expression into its two parts. First, the DIGITS operation:
DIGITS(1900000 + JULDAT)
DIGITS returns a character representation of a number. For a JULDAT field with the value 97225 or 097225, the result of this expression is 01997225.
Next, the DATE operation:
DATE(SUBSTR(DATE_A, 2, 7)
Using the SUBSTR function to “feed” the DATE function a character string exactly seven bytes long activates Query/400’s Julian date rule and results in the date 8/13/97 (the date format and separator character depend on your job’s DATFMT and DATSEP attributes).
Articles on Apis 