diff --git a/.github/workflows/release_build.yml b/.github/workflows/release_build.yml
index 0314f3c..a105de8 100644
--- a/.github/workflows/release_build.yml
+++ b/.github/workflows/release_build.yml
@@ -3,6 +3,8 @@ on:
   push:
     tags:
       - "*"
+permissions:
+  contents: write
 jobs:
   goreleaser:
     runs-on: ubuntu-latest
diff --git a/diagram/diagram.go b/diagram/diagram.go
index f04f9bf..a09b34d 100644
--- a/diagram/diagram.go
+++ b/diagram/diagram.go
@@ -57,7 +57,7 @@ func (d diagram) Create(wr io.Writer, result *database.Result) error {
 			continue
 		}
 
-		constraints = append(constraints, getConstraintData(d.config, relationshipLabelMap, constraint))
+		constraints = append(constraints, getConstraintData(d.config, relationshipLabelMap, result.Tables, constraint))
 	}
 
 	diagramData := ErdDiagramData{
diff --git a/diagram/diagram_data.go b/diagram/diagram_data.go
index 6fe72df..a13fefb 100644
--- a/diagram/diagram_data.go
+++ b/diagram/diagram_data.go
@@ -3,8 +3,10 @@ package diagram
 type ErdRelationType string
 
 const (
-	relationOneToOne  ErdRelationType = "|o--||"
-	relationManyToOne ErdRelationType = "}o--||"
+	relationOneToOne       ErdRelationType = "|o--||"
+	relationOneToMaybeOne  ErdRelationType = "|o--o|"
+	relationManyToOne      ErdRelationType = "}o--||"
+	relationManyToMaybeOne ErdRelationType = "}o--o|"
 )
 
 type ErdAttributeKey string
diff --git a/diagram/diagram_util.go b/diagram/diagram_util.go
index d8bc297..d3f92ce 100644
--- a/diagram/diagram_util.go
+++ b/diagram/diagram_util.go
@@ -10,9 +10,15 @@ import (
 	"github.com/KarnerTh/mermerd/database"
 )
 
-func getRelation(constraint database.ConstraintResult) ErdRelationType {
+func getRelation(constraint database.ConstraintResult, isUnique bool, isNullable bool) ErdRelationType {
 	if constraint.IsPrimary && !constraint.HasMultiplePK {
 		return relationOneToOne
+	} else if isUnique && isNullable {
+		return relationOneToMaybeOne
+	} else if isUnique {
+		return relationOneToOne
+	} else if isNullable {
+		return relationManyToMaybeOne
 	} else {
 		return relationManyToOne
 	}
@@ -96,7 +102,7 @@ func shouldSkipConstraint(config config.MermerdConfig, tables []ErdTableData, co
 	return !(tableNameInSlice(tables, constraint.PkTable) && tableNameInSlice(tables, constraint.FkTable))
 }
 
-func getConstraintData(config config.MermerdConfig, labelMap RelationshipLabelMap, constraint database.ConstraintResult) ErdConstraintData {
+func getConstraintData(config config.MermerdConfig, labelMap RelationshipLabelMap, tables []database.TableResult, constraint database.ConstraintResult) ErdConstraintData {
 	pkTableName := getTableName(config, database.TableDetail{Schema: constraint.PkSchema, Name: constraint.PkTable})
 	fkTableName := getTableName(config, database.TableDetail{Schema: constraint.FkSchema, Name: constraint.FkTable})
 
@@ -108,10 +114,25 @@ func getConstraintData(config config.MermerdConfig, labelMap RelationshipLabelMa
 		constraintLabel = relationshipLabel.Label
 	}
 
+	isUnique := false
+	isNullable := true
+	for _, table := range tables {
+		if table.Table.Name == constraint.FkTable && table.Table.Schema == constraint.FkSchema {
+			for _, column := range table.Columns {
+				if column.Name == constraint.ColumnName {
+					isUnique = column.IsUnique
+					isNullable = column.IsNullable
+					goto double_break
+				}
+			}
+		}
+	}
+double_break:
+
 	return ErdConstraintData{
 		PkTableName:     pkTableName,
 		FkTableName:     fkTableName,
-		Relation:        getRelation(constraint),
+		Relation:        getRelation(constraint, isUnique, isNullable),
 		ConstraintLabel: constraintLabel,
 	}
 }
diff --git a/diagram/diagram_util_test.go b/diagram/diagram_util_test.go
index 32834b5..986f772 100644
--- a/diagram/diagram_util_test.go
+++ b/diagram/diagram_util_test.go
@@ -16,11 +16,26 @@ func TestGetRelation(t *testing.T) {
 		isPrimary        bool
 		hasMultiplePK    bool
 		expectedRelation ErdRelationType
+		isUnique         bool
+		isNullable       bool
 	}{
-		{true, true, relationManyToOne},
-		{false, true, relationManyToOne},
-		{false, false, relationManyToOne},
-		{true, false, relationOneToOne},
+		{true, true, relationManyToOne, false, false},
+		{false, true, relationManyToOne, false, false},
+		{false, false, relationManyToOne, false, false},
+		{true, false, relationOneToOne, false, false},
+
+		{false, false, relationOneToMaybeOne, true, true},
+		{false, false, relationOneToOne, true, false},
+		{false, false, relationManyToMaybeOne, false, true},
+
+		{true, false, relationOneToOne, true, false},
+		// if PK is true it should not be nullable (thought technically possible in Sqlite)
+
+		{false, true, relationOneToMaybeOne, true, true},
+		{false, true, relationOneToOne, true, false},
+		{false, true, relationManyToMaybeOne, false, true},
+
+		{true, true, relationOneToOne, true, false},
 	}
 
 	for index, testCase := range testCases {
@@ -33,9 +48,11 @@ func TestGetRelation(t *testing.T) {
 				IsPrimary:      testCase.isPrimary,
 				HasMultiplePK:  testCase.hasMultiplePK,
 			}
+			isUnique := testCase.isUnique
+			isNullable := testCase.isNullable
 
 			// Act
-			result := getRelation(constraint)
+			result := getRelation(constraint, isUnique, isNullable)
 
 			// Assert
 			assert.Equal(t, testCase.expectedRelation, result)
@@ -335,9 +352,10 @@ func TestGetConstraintData(t *testing.T) {
 		configMock.On("OmitConstraintLabels").Return(false).Once()
 		configMock.On("ShowSchemaPrefix").Return(false).Twice()
 		constraint := database.ConstraintResult{ColumnName: "Column1"}
+		tables := []database.TableResult{}
 
 		// Act
-		result := getConstraintData(&configMock, &relationshipLabelMap{}, constraint)
+		result := getConstraintData(&configMock, &relationshipLabelMap{}, tables, constraint)
 
 		// Assert
 		configMock.AssertExpectations(t)
@@ -350,9 +368,10 @@ func TestGetConstraintData(t *testing.T) {
 		configMock.On("ShowSchemaPrefix").Return(false).Twice()
 
 		constraint := database.ConstraintResult{ColumnName: "Column1"}
+		tables := []database.TableResult{}
 
 		// Act
-		result := getConstraintData(&configMock, &relationshipLabelMap{}, constraint)
+		result := getConstraintData(&configMock, &relationshipLabelMap{}, tables, constraint)
 
 		// Assert
 		configMock.AssertExpectations(t)
@@ -377,8 +396,24 @@ func TestGetConstraintData(t *testing.T) {
 			ColumnName: "Column1",
 		}
 
+		tables := []database.TableResult{
+			{
+				Table: database.TableDetail{
+					Name: "pk",
+				},
+				Columns: []database.ColumnResult{
+					{
+						Name:       "Column1",
+						IsUnique:   false,
+						IsNullable: false,
+					},
+				},
+				Constraints: database.ConstraintResultList{constraint},
+			},
+		}
+
 		// Act
-		result := getConstraintData(&configMock, labelsMap, constraint)
+		result := getConstraintData(&configMock, labelsMap, tables, constraint)
 
 		// Assert
 		configMock.AssertExpectations(t)
@@ -403,8 +438,24 @@ func TestGetConstraintData(t *testing.T) {
 			ColumnName: "Column1",
 		}
 
+		tables := []database.TableResult{
+			{
+				Table: database.TableDetail{
+					Name: "pk",
+				},
+				Columns: []database.ColumnResult{
+					{
+						Name:       "Column1",
+						IsUnique:   false,
+						IsNullable: false,
+					},
+				},
+				Constraints: database.ConstraintResultList{constraint},
+			},
+		}
+
 		// Act
-		result := getConstraintData(&configMock, labelsMap, constraint)
+		result := getConstraintData(&configMock, labelsMap, tables, constraint)
 
 		// Assert
 		configMock.AssertExpectations(t)