Signal Analysis

Name: Lexega
Author: Lexega

Signal Analysis runs pre-execution checks on SQL to surface risks and governance issues (without connecting to Snowflake unless you opt into catalog pulling).

What You Get

A risk report (what was detected) via lexega-sql analyze.
Optional policy enforcement (allow/warn/block) via --policy + --env + --decision-out.

Lexega ships with hundreds of built-in rules (the exact set depends on your installed version). Rather than duplicating them here, the recommended workflow is: discover what's available from the CLI so docs never drift. For a browsable list, see Builtin Rule Reference.

Dialect Coverage

Dialect	Coverage	Signal Categories
Snowflake	Extensive	Security, governance, performance, correctness, semantics
PostgreSQL	Extensive	Security (RLS, roles, privileges), DDL governance, operations
BigQuery	Core	Data movement, governance, BQML lifecycle/security, external data paths
Databricks	Extensive	Delta operations, Unity Catalog governance, row/column security controls, storage credentials

All dialects use the same signal architecture and policy engine. Custom rules work across dialects.

Discover Rules and Signals

# List built-in rule IDs available in your version
lexega-sql analyze --list-signals

# Show which signals were extracted per statement
lexega-sql analyze --explain-signals query.sql

# Full detail mode (includes all statements/signals)
lexega-sql analyze --trace --format json query.sql

Diff Signals (Semantic Diff)

In addition to static analysis signals (emitted by lexega-sql analyze), Lexega also emits diff signals when you run Semantic Diff.

Diff signals describe semantic changes between a baseline and a head version of SQL.
They are emitted by lexega-sql diff (and by unified review workflows that include semantic diff).
Custom rules can match diff signals via diff_triggers (instead of signals). The allowed change types are validated by SemanticChangeType in the Custom Rules schema.

See: Semantic Diff

Signal Categories (for Custom Rules)

Custom rules match structured signals. The category field uses these technical categories:

SECURITY — Authentication, encryption, access control
GOVERNANCE — Policies, tags, compliance metadata
DATA_ACCESS — Table/column reads and writes
DATA_INTEGRITY — Data correctness/trustworthiness signals
PERFORMANCE — Cost and efficiency signals
OPERATIONS — Reliability/lifecycle/administrative signals
QUERY — Query pattern signals
SEMANTICS — SQL logic hazards (NULL handling, 3-valued logic, etc.)