Predicate syntax

delta-explain accepts standard SQL WHERE-clause syntax, parsed via sqlparser-rs.

-- Comparisons
age > 30
country = 'DE'
score >= 90.5

-- Logical operators
age > 30 AND country = 'DE'
country = 'DE' OR country = 'IT'
NOT country = 'US'

-- IN lists
country IN ('DE', 'IT', 'US')
country NOT IN ('US')

-- BETWEEN
age BETWEEN 20 AND 40

-- NULL checks
name IS NOT NULL
age IS NULL

-- Parentheses
(country = 'DE' OR country = 'IT') AND age > 30

-- Nested columns
payload.age > 30

Also supported: IS [NOT] DISTINCT FROM, DATE '...' / TIMESTAMP '...' literal forms, schema-driven coercion (a quoted '2026-07-01' against a DATE column just works, including DECIMAL and narrow integers), and LIKE: prefix patterns (country LIKE 'D%') prune on partition values and on string min/max statistics, and on partition columns every other shape ('%son', _, NOT LIKE) prunes exactly too.

Subqueries, functions, and non-prefix LIKE on data columns are outside the pruning language: they warn and keep files instead of failing. The exact rules are the degradation rules in the semantics contract.

What the analysis shows

The analysis block always displays the predicate as analyzed, so normalization is visible rather than silent. A prefix LIKE appears as the lexicographic range it was rewritten to, and prunes through the ordinary partition rules:

$ delta-explain ./table -w "country LIKE 'D%' AND age > 40"

Predicate Analysis:
  partition-safe: country >= 'D' AND country < 'E'
  stats-safe:     age > 40
  stats coverage:
    age [min_max]: 2/2 candidate files (100%)
  unsplittable:   -
  confidence:     conservative

Files in snapshot: 6

Phase 1: Partition pruning [exact]
  predicate:       country >= 'D' AND country < 'E'
  files remaining: 2  (-4, 67% pruned)

Phase 2: Data skipping (min/max statistics) [conservative]
  predicate:       age > 40
  files remaining: 1  (-1, 50% pruned)

Total reduction: 6 -> 1 files (83% pruned)

A construct outside the pruning language degrades loudly instead of erroring: the fragment routes to unsplittable, confidence drops to incomplete, a warning names the offending expression, and the sibling conjunct still prunes:

$ delta-explain ./table -w "UPPER(country) = 'DE' AND age > 40"

Predicate Analysis:
  partition-safe: -
  stats-safe:     age > 40
  stats coverage:
    age [min_max]: 6/6 candidate files (100%)
  unsplittable:   UPPER(country) = 'DE'
  confidence:     incomplete

Files in snapshot: 6

Phase 1: Data skipping (min/max statistics) [incomplete]
  predicate:       age > 40  (+1 unsupported fragment, keeps all files)
  files remaining: 3  (-3, 50% pruned)

Warnings!
[UNSUPPORTED_EXPRESSION]: Unsupported expression: UPPER(country); the fragment 'UPPER(country) = 'DE'' cannot contribute to pruning and is applied conservatively (keeps all files)