Preserve UNIQUE NULLS NOT DISTINCT

cmd/dump/dump_integration_test.go

@@ -137,6 +137,13 @@ func TestDumpCommand_Issue396CheckConstraintIsNotNull(t *testing.T) {
 	runExactMatchTest(t, "issue_396_check_constraint_is_not_null")
 }
 
+func TestDumpCommand_Issue412UniqueNullsNotDistinct(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping integration test in short mode")
+	}
+	runExactMatchTest(t, "issue_412_unique_nulls_not_distinct")
+}
+
 func TestDumpCommand_Issue191FunctionProcedureOverload(t *testing.T) {
 	if testing.Short() {
 		t.Skip("Skipping integration test in short mode")

internal/diff/constraint.go

@@ -32,7 +32,11 @@ func generateConstraintSQL(constraint *ir.Constraint, targetSchema string) strin
 		if constraint.IsTemporal && len(cols) > 0 {
 			cols[len(cols)-1] = cols[len(cols)-1] + " WITHOUT OVERLAPS"
 		}
-		return fmt.Sprintf("CONSTRAINT %s UNIQUE (%s)", ir.QuoteIdentifier(constraint.Name), strings.Join(cols, ", "))
+		modifier := ""
+		if constraint.NullsNotDistinct {
+			modifier = " NULLS NOT DISTINCT"
+		}
+		return fmt.Sprintf("CONSTRAINT %s UNIQUE%s (%s)", ir.QuoteIdentifier(constraint.Name), modifier, strings.Join(cols, ", "))
 	case ir.ConstraintTypeForeignKey:
 		// Always include CONSTRAINT name to preserve explicit FK names
 		// Use QualifyEntityNameWithQuotes to add schema qualifier when referencing tables in other schemas
@@ -176,6 +180,9 @@ func constraintsEqual(old, new *ir.Constraint) bool {
 	if old.IsTemporal != new.IsTemporal {
 		return false
 	}
+	if old.NullsNotDistinct != new.NullsNotDistinct {
+		return false
+	}
 
 	// Validation status - only compare for CHECK and FOREIGN KEY constraints
 	// PRIMARY KEY and UNIQUE constraints are always valid (IsValid is not meaningful for them)

internal/diff/table.go

@@ -774,7 +774,11 @@ func (td *tableDiff) generateAlterTableStatements(targetSchema string, collector
 				case ir.ConstraintTypePrimaryKey:
 					inlineConstraint = fmt.Sprintf(" CONSTRAINT %s PRIMARY KEY", ir.QuoteIdentifier(constraint.Name))
 				case ir.ConstraintTypeUnique:
-					inlineConstraint = fmt.Sprintf(" CONSTRAINT %s UNIQUE", ir.QuoteIdentifier(constraint.Name))
+					modifier := ""
+					if constraint.NullsNotDistinct {
+						modifier = " NULLS NOT DISTINCT"
+					}
+					inlineConstraint = fmt.Sprintf(" CONSTRAINT %s UNIQUE%s", ir.QuoteIdentifier(constraint.Name), modifier)
 				case ir.ConstraintTypeForeignKey:
 					// For FK, use the generateForeignKeyClause with inline=true
 					fkClause := generateForeignKeyClause(constraint, targetSchema, true)
@@ -876,8 +880,12 @@ func (td *tableDiff) generateAlterTableStatements(targetSchema string, collector
 				columnNames[len(columnNames)-1] = columnNames[len(columnNames)-1] + " WITHOUT OVERLAPS"
 			}
 			tableName := getTableNameWithSchema(td.Table.Schema, td.Table.Name, targetSchema)
-			sql := fmt.Sprintf("ALTER TABLE %s\nADD CONSTRAINT %s UNIQUE (%s);",
-				tableName, ir.QuoteIdentifier(constraint.Name), strings.Join(columnNames, ", "))
+			modifier := ""
+			if constraint.NullsNotDistinct {
+				modifier = " NULLS NOT DISTINCT"
+			}
+			sql := fmt.Sprintf("ALTER TABLE %s\nADD CONSTRAINT %s UNIQUE%s (%s);",
+				tableName, ir.QuoteIdentifier(constraint.Name), modifier, strings.Join(columnNames, ", "))
 
 			context := &diffContext{
 				Type:                DiffTypeTableConstraint,
@@ -1004,8 +1012,12 @@ func (td *tableDiff) generateAlterTableStatements(targetSchema string, collector
 			if constraint.IsTemporal && len(columnNames) > 0 {
 				columnNames[len(columnNames)-1] = columnNames[len(columnNames)-1] + " WITHOUT OVERLAPS"
 			}
-			addSQL = fmt.Sprintf("ALTER TABLE %s\nADD CONSTRAINT %s UNIQUE (%s);",
-				tableName, ir.QuoteIdentifier(constraint.Name), strings.Join(columnNames, ", "))
+			modifier := ""
+			if constraint.NullsNotDistinct {
+				modifier = " NULLS NOT DISTINCT"
+			}
+			addSQL = fmt.Sprintf("ALTER TABLE %s\nADD CONSTRAINT %s UNIQUE%s (%s);",
+				tableName, ir.QuoteIdentifier(constraint.Name), modifier, strings.Join(columnNames, ", "))
 
 		case ir.ConstraintTypeCheck:
 			// Add CHECK constraint with ensured outer parentheses

ir/inspector.go

@@ -486,13 +486,14 @@ func (i *Inspector) buildConstraints(ctx context.Context, schema *IR, targetSche
 			}
 
 			c = &Constraint{
-				Schema:     schemaName,
-				Table:      tableName,
-				Name:       constraintName,
-				Type:       cType,
-				Columns:    []*ConstraintColumn{},
-				NoInherit:  constraint.NoInherit,
-				IsTemporal: constraint.IsPeriod.Bool, // PG18 temporal constraint (WITHOUT OVERLAPS / PERIOD)
+				Schema:           schemaName,
+				Table:            tableName,
+				Name:             constraintName,
+				Type:             cType,
+				Columns:          []*ConstraintColumn{},
+				NoInherit:        constraint.NoInherit,
+				IsTemporal:       constraint.IsPeriod.Bool,         // PG18 temporal constraint (WITHOUT OVERLAPS / PERIOD)
+				NullsNotDistinct: constraint.NullsNotDistinct.Bool, // PG15+ UNIQUE NULLS NOT DISTINCT
 			}
 
 			// Handle foreign key references

ir/ir.go

@@ -222,8 +222,9 @@ type Constraint struct {
 	Deferrable          bool                `json:"deferrable,omitempty"`
 	InitiallyDeferred   bool                `json:"initially_deferred,omitempty"`
 	IsValid             bool                `json:"is_valid,omitempty"`
-	NoInherit           bool                `json:"no_inherit,omitempty"` // CHECK constraint NO INHERIT modifier
-	IsTemporal          bool                `json:"is_temporal,omitempty"` // PG18: temporal constraint (WITHOUT OVERLAPS on PK/UNIQUE, PERIOD on FK)
+	NoInherit           bool                `json:"no_inherit,omitempty"`         // CHECK constraint NO INHERIT modifier
+	IsTemporal          bool                `json:"is_temporal,omitempty"`        // PG18: temporal constraint (WITHOUT OVERLAPS on PK/UNIQUE, PERIOD on FK)
+	NullsNotDistinct    bool                `json:"nulls_not_distinct,omitempty"` // PG15+: UNIQUE constraint treats NULLs as not distinct
 	Comment             string              `json:"comment,omitempty"`
 }
 

ir/queries/queries.sql

@@ -930,14 +930,18 @@ SELECT
     c.condeferred AS initially_deferred,
     c.convalidated AS is_valid,
     COALESCE((to_jsonb(c) ->> 'conperiod')::boolean, false) AS is_period,
-    c.connoinherit AS no_inherit
+    c.connoinherit AS no_inherit,
+    -- pg_index.indnullsnotdistinct is PG15+. Use to_jsonb so the column reference
+    -- doesn't fail to plan on PG14 (where the attribute does not exist on pg_index).
+    COALESCE((to_jsonb(i) ->> 'indnullsnotdistinct')::boolean, false) AS nulls_not_distinct
 FROM pg_constraint c
 JOIN pg_class cl ON c.conrelid = cl.oid
 JOIN pg_namespace n ON cl.relnamespace = n.oid
 LEFT JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)
 LEFT JOIN pg_class fcl ON c.confrelid = fcl.oid
 LEFT JOIN pg_namespace fn ON fcl.relnamespace = fn.oid
 LEFT JOIN pg_attribute fa ON fa.attrelid = c.confrelid AND fa.attnum = c.confkey[array_position(c.conkey, a.attnum)]
+LEFT JOIN pg_index i ON i.indexrelid = c.conindid
 WHERE n.nspname = $1
 ORDER BY n.nspname, cl.relname, c.contype, c.conname, a.attnum;
 

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/diff.sql

@@ -0,0 +1,2 @@
+ALTER TABLE pgschema_repro_nulls
+ADD CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b);

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/new.sql

@@ -0,0 +1,11 @@
+-- Regression for: UNIQUE NULLS NOT DISTINCT modifier dropped from constraints
+-- Add a table-level UNIQUE constraint with the NULLS NOT DISTINCT modifier
+-- (PostgreSQL 15+). Without the fix, the inspector loses the modifier and the
+-- generated migration emits a plain UNIQUE (a, b) — silently changing the
+-- semantics of the constraint and breaking INSERT ... ON CONFLICT flows that
+-- rely on NULLs colliding.
+CREATE TABLE public.pgschema_repro_nulls (
+    a integer,
+    b integer,
+    CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b)
+);

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/old.sql

@@ -0,0 +1,6 @@
+-- Regression for: UNIQUE NULLS NOT DISTINCT modifier dropped from constraints
+-- The starting state has no UNIQUE constraint at all; we add one in new.sql.
+CREATE TABLE public.pgschema_repro_nulls (
+    a integer,
+    b integer
+);

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/plan.json

@@ -0,0 +1,20 @@
+{
+  "version": "1.0.0",
+  "pgschema_version": "1.9.0",
+  "created_at": "1970-01-01T00:00:00Z",
+  "source_fingerprint": {
+    "hash": "70a4465367d5d40d0149eadc73c423f9eb954838b6602f00ca3496b264baf2e9"
+  },
+  "groups": [
+    {
+      "steps": [
+        {
+          "sql": "ALTER TABLE pgschema_repro_nulls\nADD CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b);",
+          "type": "table.constraint",
+          "operation": "create",
+          "path": "public.pgschema_repro_nulls.pgschema_repro_nulls_uniq"
+        }
+      ]
+    }
+  ]
+}

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/plan.sql

@@ -0,0 +1,2 @@
+ALTER TABLE pgschema_repro_nulls
+ADD CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b);

testdata/diff/create_table/add_unique_constraint_nulls_not_distinct/plan.txt

@@ -0,0 +1,14 @@
+Plan: 1 to modify.
+
+Summary by type:
+  tables: 1 to modify
+
+Tables:
+  ~ pgschema_repro_nulls
+    + pgschema_repro_nulls_uniq (constraint)
+
+DDL to be executed:
+--------------------------------------------------
+
+ALTER TABLE pgschema_repro_nulls
+ADD CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b);

testdata/dump/issue_412_unique_nulls_not_distinct/manifest.json

@@ -0,0 +1,9 @@
+{
+  "name": "issue_412_unique_nulls_not_distinct",
+  "description": "pgschema dump silently drops the NULLS NOT DISTINCT modifier from UNIQUE table constraints",
+  "source": "https://github.com/pgplex/pgschema/issues/412",
+  "notes": [
+    "NULLS NOT DISTINCT was introduced in PostgreSQL 15; the underlying pg_index.indnullsnotdistinct column does not exist on PG14.",
+    "The inspector exposes the modifier on UNIQUE constraints by joining pg_index via conindid and reading indnullsnotdistinct defensively (to_jsonb), which collapses to false on PG14."
+  ]
+}

testdata/dump/issue_412_unique_nulls_not_distinct/pgdump.sql

@@ -0,0 +1,32 @@
+--
+-- PostgreSQL database dump
+--
+
+SET statement_timeout = 0;
+SET lock_timeout = 0;
+-- SET transaction_timeout = 0;
+SET client_encoding = 'UTF8';
+SET standard_conforming_strings = on;
+SET check_function_bodies = false;
+SET client_min_messages = warning;
+SET row_security = off;
+
+--
+-- Name: pgschema_repro_nulls; Type: TABLE; Schema: public; Owner: -
+--
+
+CREATE TABLE public.pgschema_repro_nulls (
+    a integer,
+    b integer
+);
+
+--
+-- Name: pgschema_repro_nulls pgschema_repro_nulls_uniq; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.pgschema_repro_nulls
+    ADD CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b);
+
+--
+-- PostgreSQL database dump complete
+--

testdata/dump/issue_412_unique_nulls_not_distinct/pgschema.sql

@@ -0,0 +1,18 @@
+--
+-- pgschema database dump
+--
+
+-- Dumped from database version PostgreSQL 18.0
+-- Dumped by pgschema version 1.9.0
+
+
+--
+-- Name: pgschema_repro_nulls; Type: TABLE; Schema: -; Owner: -
+--
+
+CREATE TABLE IF NOT EXISTS pgschema_repro_nulls (
+    a integer,
+    b integer,
+    CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b)
+);
+

testdata/dump/issue_412_unique_nulls_not_distinct/raw.sql

@@ -0,0 +1,14 @@
+--
+-- Test case for GitHub issue #412: UNIQUE NULLS NOT DISTINCT dropped from dump
+--
+-- The NULLS NOT DISTINCT modifier (PostgreSQL 15+) makes NULL-bearing tuples
+-- collide for uniqueness purposes, which is the opposite of the SQL default.
+-- pgschema dump used to silently drop the modifier, emitting a plain
+-- UNIQUE (...) constraint and quietly changing semantics.
+--
+
+CREATE TABLE pgschema_repro_nulls (
+    a integer,
+    b integer,
+    CONSTRAINT pgschema_repro_nulls_uniq UNIQUE NULLS NOT DISTINCT (a, b)
+);

testutil/skip_list.go

@@ -68,6 +68,8 @@ var skipListRequiresExtension = []string{
 // These tests use features not available in PostgreSQL 14 (e.g., NULLS NOT DISTINCT is PG15+).
 var skipListPG14 = []string{
 	"create_index/add_index",
+	"create_table/add_unique_constraint_nulls_not_distinct",
+	"TestDumpCommand_Issue412UniqueNullsNotDistinct",
 }
 
 // skipListPG14_17 defines test cases that should be skipped for PostgreSQL 14-17.