# transform_null_equals

> transform_null_equals — Treats "expr=NULL" as "expr IS NULL". Observed in PG9.0–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Treats "expr=NULL" as "expr IS NULL".”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `bool` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Version and Platform Compatibility / Other Platforms and Clients | Upstream classification |
| Latest boot value | `off` | off |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.0 (research boundary) |
| Present in | PG9.0–19 Beta 3 |
| Removed in | No |
| Introduction commit | Not asserted: predates the PG9.0 research boundary |
| Commit date | — |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.0–19 Beta 3 | `off` | — | off |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Treats "expr=NULL" as "expr IS NULL". It can be changed at session scope, so different sessions may observe different behavior.

The parser rewrites expr = NULL to expr IS NULL for broken legacy clients. SQL's normal three-valued semantics make equality with NULL yield unknown, so enabling this can hide application defects and does not rewrite other NULL comparisons.

Monitor and change transform_null_equals together with array_nulls, backslash_quote, escape_string_warning. Validate on the relevant server role and real workload, then use its user context to choose session change, reload, or restart; a historical boot default is not the current effective value.

## Tuning advice {#tuning-advice}

> [!TIP]
> **Advice.** These are workload-specific starting points and must be validated with measurements.

| Workload | Guidance |
| --- | --- |
| OLTP | Keep the modern default and repair legacy clients/SQL that depend on transform_null_equals. Test migration at session scope first; do not make a compatibility switch permanent cluster policy. |
| OLAP | Regression-test ETL, generated SQL, and old drivers, where parsing/quoting assumptions hide. Performance is rarely a reason to change this switch. |
| Small nodes | Keep the default without a legacy requirement. If temporarily enabled, record owner, affected connections, and a removal date. |
{.full-width}

## Pigsty {#pigsty}

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

| Template | Effective value | Versus upstream boot | Source expression |
| --- | --- | --- | --- |
| OLTP | Unmodified | — | — |
| OLAP | Unmodified | — | — |
| CRIT | Unmodified | — | — |
| TINY | Unmodified | — | — |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Keeping a compatibility switch permanently instead of fixing the client.
- Testing in one session and deploying globally to unrelated applications.
- Confusing parsing compatibility with data or security compatibility.
- Forgetting to remove an override after the upgrade migration is complete.

## Related parameters {#related-parameters}

[`array_nulls`](/parameters/array-nulls/) · [`backslash_quote`](/parameters/backslash-quote/) · [`escape_string_warning`](/parameters/escape-string-warning/) · [`standard_conforming_strings`](/parameters/standard-conforming-strings/) · [`quote_all_identifiers`](/parameters/quote-all-identifiers/) · [`allow_alter_system`](/parameters/allow-alter-system/)

## References {#references}

- [PostgreSQL 19 Beta 3 — transform_null_equals](https://www.postgresql.org/docs/19/runtime-config-compatible.html#GUC-TRANSFORM-NULL-EQUALS)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)