Comparison of date fields

Date fields can be alphanumeric category, zoned decimal, or internal decimal; the existing rules for the validity and comparison type (numeric or alphanumeric) apply. For example, an alphanumeric date field cannot be compared with an internal decimal date field. In addition to these rules, two date fields can be compared only if they are compatible; they must have the same date format except for the year part, which can be windowed or expanded.

For year-last date fields, the only comparisons that are supported are IS EQUAL TO and IS NOT EQUAL TO between two year-last date fields with identical date formats, or between a year-last date field and a nondate.

Table 1 shows supported comparisons for nonyear-last date fields. This table uses the following terms to describe how the comparisons are performed:

Nonwindowed
The comparison is performed with no windowing, as if the operands were both nondates.
Windowed
The comparison is performed as if:
  1. Any windowed date field in the relation were expanded according to the century window specified by the YEARWINDOW compiler option, as described under Semantics of windowed date fields.
  2. Any repetitive alphanumeric figurative constant were expanded to the size of the windowed date field with which it is compared, giving an alphanumeric nondate comparand. Repetitive alphanumeric figurative constants include ZERO (in an alphanumeric context), SPACE, LOW-VALUE, HIGH-VALUE, QUOTE and ALL literal.
  3. Any nondate operands were treated as if they had the same date format as the date field, but with a base year of 1900.

The comparison is then performed according to normal COBOL rules. Alphanumeric comparisons are not changed to numeric comparisons by the prefixing of the century value.

Table 1. Comparisons with date fields
 


Nondate
second operand

Windowed
date field
second operand

Expanded
date field
second operand

Nondate
first operand

Nonwindowed Windowed1 Nonwindowed

Windowed date field
first operand

Windowed1 Windowed Windowed

Expanded date field
first operand

Nonwindowed Windowed Nonwindowed
  1. When compared with windowed date fields, nondates are assumed to contain a windowed year relative to 1900. For details, see item 3 under the definition of "Windowed" comparison.

Relation conditions can contain arithmetic expressions. For information about the treatment of date fields in arithmetic expressions, see Arithmetic with date fields.