Conditional CHAR vs VARCHAR as needed by mysql

query.go

@@ -10,6 +10,19 @@ import (
 
 const tagName = "gormlike"
 
+func likeCastType(dialect string) string {
+	switch strings.ToLower(dialect) {
+	case "mysql", "mariadb":
+		return "CHAR"
+	default:
+		return "VARCHAR"
+	}
+}
+
+func likeCondition(dialect, column string) string {
+	return fmt.Sprintf("CAST(%s as %s) LIKE ?", column, likeCastType(dialect))
+}
+
 //nolint:gocognit,cyclop // is a complex, recursive function
 func (d *gormLike) replaceExpressions(db *gorm.DB, expressions []clause.Expression) []clause.Expression {
 	for index, cond := range expressions {
@@ -55,7 +68,7 @@ func (d *gormLike) replaceExpressions(db *gorm.DB, expressions []clause.Expressi
 				continue
 			}
 
-			condition := fmt.Sprintf("CAST(%s as varchar) LIKE ?", column.Name)
+			condition := likeCondition(db.Dialector.Name(), column.Name)
 
 			if d.replaceCharacter != "" {
 				value = strings.ReplaceAll(value, d.replaceCharacter, "%")
@@ -99,7 +112,7 @@ func (d *gormLike) replaceExpressions(db *gorm.DB, expressions []clause.Expressi
 
 				// If there are no % AND there aren't only replaceable characters, just skip it because it's a normal query
 				if strings.Contains(value, "%") || (d.replaceCharacter != "" && strings.Contains(value, d.replaceCharacter)) {
-					condition = fmt.Sprintf("CAST(%s as varchar) LIKE ?", column.Name)
+					condition = likeCondition(db.Dialector.Name(), column.Name)
 
 					if d.replaceCharacter != "" {
 						value = strings.ReplaceAll(value, d.replaceCharacter, "%")

query_test.go

@@ -10,6 +10,51 @@ import (
 	"gorm.io/gorm"
 )
 
+func TestLikeCastType(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]struct {
+		dialect  string
+		expected string
+	}{
+		"mysql uses char": {
+			dialect:  "mysql",
+			expected: "CHAR",
+		},
+		"mariadb uses char": {
+			dialect:  "mariadb",
+			expected: "CHAR",
+		},
+		"case-insensitive mysql": {
+			dialect:  "MySQL",
+			expected: "CHAR",
+		},
+		"postgres defaults to varchar": {
+			dialect:  "postgres",
+			expected: "VARCHAR",
+		},
+		"sqlite defaults to varchar": {
+			dialect:  "sqlite",
+			expected: "VARCHAR",
+		},
+	}
+
+	for name, testData := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			assert.Equal(t, testData.expected, likeCastType(testData.dialect))
+		})
+	}
+}
+
+func TestLikeCondition(t *testing.T) {
+	t.Parallel()
+
+	assert.Equal(t, "CAST(type as CHAR) LIKE ?", likeCondition("mysql", "type"))
+	assert.Equal(t, "CAST(type as VARCHAR) LIKE ?", likeCondition("postgres", "type"))
+}
+
 //nolint:maintidx // Acceptable
 func TestGormLike_Initialize_TriggersLikingCorrectly(t *testing.T) {
 	t.Parallel()