Fix Column Duplication

Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="coverlet.collector" Version="10.0.1" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="10.0.300" />
     <PackageVersion Include="Npgsql.DependencyInjection" Version="10.0.3" />
-    <PackageVersion Include="NSchema.Core" Version="3.0.0-alpha.41" />
+    <PackageVersion Include="NSchema.Core" Version="3.0.0-alpha.42" />
     <PackageVersion Include="Testcontainers" Version="4.12.0" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.6.0" />
     <PackageVersion Include="Npgsql" Version="10.0.3" />

src/NSchema.Postgres/NSchema.Postgres.csproj

@@ -20,7 +20,7 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
-    <Version>3.0.0-alpha.12</Version>
+    <Version>3.0.0-beta.1</Version>
     <AssemblyVersion>$(Version.Split('-')[0])</AssemblyVersion>
     <FileVersion>$(Version.Split('-')[0])</FileVersion>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>

src/NSchema.Postgres/Sql/PostgresSchemaProvider.cs

@@ -132,10 +132,10 @@ private static async Task<List<ColumnRow>> QueryColumns(NpgsqlConnection conn, s
                 seq.seqincrement AS identity_increment,
                 CASE WHEN c.is_generated = 'ALWAYS' THEN c.generation_expression END AS generation_expression
             FROM information_schema.columns c
+            LEFT JOIN pg_namespace    n  ON n.nspname   = c.table_schema
             LEFT JOIN pg_class        t  ON t.relname   = c.table_name
+                                        AND t.relnamespace = n.oid
                                         AND t.relkind   = 'r'
-            LEFT JOIN pg_namespace    n  ON n.oid        = t.relnamespace
-                                        AND n.nspname   = c.table_schema
             LEFT JOIN pg_attribute    a  ON a.attrelid  = t.oid
                                         AND a.attname   = c.column_name
             LEFT JOIN pg_depend       d  ON d.refobjid  = t.oid

tests/NSchema.Postgres.Tests/Sql/PostgresSchemaProviderTests.cs

@@ -1042,4 +1042,45 @@ public async Task GetSchema_Extensions_AreReportedAtRootWithVersion()
         citext.Version.ShouldNotBeNull();
         schema.Extensions.ShouldNotContain(e => e.Name == "plpgsql");
     }
+
+    // ── Same table name across schemas ────────────────────────────────────────
+
+    // Regression: the columns query joined pg_class on relname alone (not namespace), so a table name shared by
+    // two schemas matched both pg_class rows and fanned every column row out once per schema — columns appeared
+    // duplicated in each table. Each table must report only its own columns.
+    [Fact]
+    public async Task GetSchema_SameTableNameInDifferentSchemas_DoesNotDuplicateColumns()
+    {
+        // Arrange
+        var other = $"test_{Guid.NewGuid():N}";
+        await Exec($"CREATE SCHEMA \"{other}\"");
+        try
+        {
+            await Exec($"""
+                CREATE TABLE "{_schema}".users (
+                    id   INTEGER NOT NULL,
+                    name TEXT    NOT NULL
+                )
+                """);
+            await Exec($"""
+                CREATE TABLE "{other}".users (
+                    code   INTEGER NOT NULL,
+                    region TEXT    NOT NULL
+                )
+                """);
+
+            // Act
+            var model = await _sut.GetSchema([_schema, other], TestContext.Current.CancellationToken);
+
+            // Assert
+            var primary = model.Schemas.Single(s => s.Name == _schema).Tables.Single(t => t.Name == "users");
+            var secondary = model.Schemas.Single(s => s.Name == other).Tables.Single(t => t.Name == "users");
+            primary.Columns.Select(c => c.Name).ShouldBe(["id", "name"]);
+            secondary.Columns.Select(c => c.Name).ShouldBe(["code", "region"]);
+        }
+        finally
+        {
+            await Exec($"DROP SCHEMA IF EXISTS \"{other}\" CASCADE");
+        }
+    }
 }