diff --git a/clause/where.go b/clause/where.go
index 9af9701c..a3774e1c 100644
--- a/clause/where.go
+++ b/clause/where.go
@@ -1,5 +1,9 @@
 package clause
 
+import (
+	"strings"
+)
+
 // Where where clause
 type Where struct {
 	Exprs []Expression
@@ -22,6 +26,7 @@ func (where Where) Build(builder Builder) {
 		}
 	}
 
+	wrapInParentheses := false
 	for idx, expr := range where.Exprs {
 		if idx > 0 {
 			if v, ok := expr.(OrConditions); ok && len(v.Exprs) == 1 {
@@ -31,7 +36,36 @@ func (where Where) Build(builder Builder) {
 			}
 		}
 
-		expr.Build(builder)
+		if len(where.Exprs) > 1 {
+			switch v := expr.(type) {
+			case OrConditions:
+				if len(v.Exprs) == 1 {
+					if e, ok := v.Exprs[0].(Expr); ok {
+						sql := strings.ToLower(e.SQL)
+						wrapInParentheses = strings.Contains(sql, "and") || strings.Contains(sql, "or")
+					}
+				}
+			case AndConditions:
+				if len(v.Exprs) == 1 {
+					if e, ok := v.Exprs[0].(Expr); ok {
+						sql := strings.ToLower(e.SQL)
+						wrapInParentheses = strings.Contains(sql, "and") || strings.Contains(sql, "or")
+					}
+				}
+			case Expr:
+				sql := strings.ToLower(v.SQL)
+				wrapInParentheses = strings.Contains(sql, "and") || strings.Contains(sql, "or")
+			}
+		}
+
+		if wrapInParentheses {
+			builder.WriteString(`(`)
+			expr.Build(builder)
+			builder.WriteString(`)`)
+			wrapInParentheses = false
+		} else {
+			expr.Build(builder)
+		}
 	}
 }
 
@@ -50,6 +84,8 @@ func (where Where) MergeClause(clause *Clause) {
 func And(exprs ...Expression) Expression {
 	if len(exprs) == 0 {
 		return nil
+	} else if len(exprs) == 1 {
+		return exprs[0]
 	}
 	return AndConditions{Exprs: exprs}
 }
@@ -118,6 +154,7 @@ func (not NotConditions) Build(builder Builder) {
 	if len(not.Exprs) > 1 {
 		builder.WriteByte('(')
 	}
+
 	for idx, c := range not.Exprs {
 		if idx > 0 {
 			builder.WriteString(" AND ")
@@ -127,9 +164,22 @@ func (not NotConditions) Build(builder Builder) {
 			negationBuilder.NegationBuild(builder)
 		} else {
 			builder.WriteString("NOT ")
+			e, wrapInParentheses := c.(Expr)
+			if wrapInParentheses {
+				sql := strings.ToLower(e.SQL)
+				if wrapInParentheses = strings.Contains(sql, "and") || strings.Contains(sql, "or"); wrapInParentheses {
+					builder.WriteByte('(')
+				}
+			}
+
 			c.Build(builder)
+
+			if wrapInParentheses {
+				builder.WriteByte(')')
+			}
 		}
 	}
+
 	if len(not.Exprs) > 1 {
 		builder.WriteByte(')')
 	}
diff --git a/tests/sql_builder_test.go b/tests/sql_builder_test.go
index e6038947..c0176fc3 100644
--- a/tests/sql_builder_test.go
+++ b/tests/sql_builder_test.go
@@ -1,6 +1,7 @@
 package tests_test
 
 import (
+	"regexp"
 	"strings"
 	"testing"
 
@@ -188,3 +189,56 @@ func TestGroupConditions(t *testing.T) {
 		t.Errorf("expects: %v, got %v", expects, result)
 	}
 }
+
+func TestCombineStringConditions(t *testing.T) {
+	dryRunDB := DB.Session(&gorm.Session{DryRun: true})
+	sql := dryRunDB.Where("a = ? or b = ?", "a", "b").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Or("c = ? and d = ?", "c", "d").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) OR \(c = .+ and d = .+\) AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Or("c = ?", "c").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) OR c = .+ AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Or("c = ? and d = ?", "c", "d").Or("e = ? and f = ?", "e", "f").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) OR \(c = .+ and d = .+\) OR \(e = .+ and f = .+\) AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Where("c = ? and d = ?", "c", "d").Not("e = ? and f = ?", "e", "f").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) AND \(c = .+ and d = .+\) AND NOT \(e = .+ and f = .+\) AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Where("c = ?", "c").Not("e = ? and f = ?", "e", "f").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) AND c = .+ AND NOT \(e = .+ and f = .+\) AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Where("c = ? and d = ?", "c", "d").Not("e = ?", "e").Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE \(a = .+ or b = .+\) AND \(c = .+ and d = .+\) AND NOT e = .+ AND .users.\..deleted_at. IS NULL`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Where("a = ? or b = ?", "a", "b").Unscoped().Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE a = .+ or b = .+$`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Or("a = ? or b = ?", "a", "b").Unscoped().Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE a = .+ or b = .+$`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+
+	sql = dryRunDB.Not("a = ? or b = ?", "a", "b").Unscoped().Find(&User{}).Statement.SQL.String()
+	if !regexp.MustCompile(`WHERE NOT \(a = .+ or b = .+\)$`).MatchString(sql) {
+		t.Fatalf("invalid sql generated, got %v", sql)
+	}
+}