Two KQL restrictions on the same property separated by a space are OR-ed — a range needs AND

Symptom

You page through a large result set by value instead of by startrow — "files at least 1 MB, largest first, next batch is everything up to the smallest size we've seen" — and build each query by appending a restriction:

IsDocument:1 Size>=1048576 Size<=2000000

The query returns far more rows than expected: every file of 1 MB or more plus every file up to 2 MB. Your continuation never shrinks, and nothing errors. A unit test that only compares the query string passes, and a live test in a mode without the lower bound (IsDocument:1 Size<=2000000) behaves correctly, so the bug hides until both bounds meet.

Cause

KQL's implicit operator between restrictions depends on the property:

Restrictions on different properties (IsDocument:1 FileExtension:pdf) are AND-ed, which is why the habit of "just append another restriction" usually works.

Fix

• Build the restriction on one property in one place and join the bounds with AND (or use the a..b range form):

function sizeClause(min, max) {
  if (max === undefined) return 'Size>=' + min;
  return min === max ? 'Size=' + min : '(Size>=' + min + ' AND Size<=' + max + ')';
}

• The same rule (documented in the KQL syntax reference for repeated property restrictions) applies to dates: LastModifiedTime>=2026-01-01 LastModifiedTime<=2026-06-30 is an OR; write LastModifiedTime:2026-01-01..2026-06-30 or use AND.
• Test the query live in every mode that composes it and compare row counts, not just the string.

Related trap: a value cursor must handle a value larger than one batch

If you continue with Size<=smallestSeen and an entire batch has the same size (more files of one size than the batch cap), moving the cursor below that size silently skips the rest of them. Read that one size separately (Size=X, paged with startrow) before continuing from X-1. A secondary sort on [DocId] / DocId is rejected by Search REST ("We didn't understand your search terms"), so it can't serve as a tie-breaker.

See also

• Microsoft: KQL syntax reference – multiple property restrictions (union for the same property, intersection for different ones; the date-range example there uses AND)
• An unparenthesized OR silently escapes your scope filter
• Search queries that actually work