diff --git a/ddlmod.go b/ddlmod.go
index d00f3ef..9301848 100644
--- a/ddlmod.go
+++ b/ddlmod.go
@@ -14,7 +14,7 @@ import (
 var (
 	sqliteSeparator    = "`|\"|'"
 	sqliteColumnQuote  = "`"
-	uniqueRegexp       = regexp.MustCompile(fmt.Sprintf(`^(?:CONSTRAINT [%v]?[\w-]+[%v]? )?UNIQUE (.*)$`, sqliteSeparator, sqliteSeparator))
+	uniqueRegexp       = regexp.MustCompile(fmt.Sprintf(`^(?i)(?:CONSTRAINT [%v]?[\w-]+[%v]? )?UNIQUE\s*(\(.*)$`, sqliteSeparator, sqliteSeparator))
 	indexRegexp        = regexp.MustCompile(fmt.Sprintf(`(?is)CREATE(?: UNIQUE)? INDEX [%v]?[\w\d-]+[%v]?(?s:.*?)ON (.*)$`, sqliteSeparator, sqliteSeparator))
 	tableRegexp        = regexp.MustCompile(fmt.Sprintf(`(?is)(CREATE TABLE [%v]?[\w\d-]+[%v]?)(?:\s*\((.*)\))?(.*)$`, sqliteSeparator, sqliteSeparator))
 	checkRegexp        = regexp.MustCompile(`^(?i)CHECK[\s]*\(`)
@@ -217,7 +217,9 @@ func (d *ddl) renameTable(dst, src string) error {
 }
 
 func compileConstraintRegexp(name string) *regexp.Regexp {
-	return regexp.MustCompile("^(?i:CONSTRAINT)\\s+[\"`]?" + regexp.QuoteMeta(name) + "[\"`\\s]")
+	// the name may be quoted with backquotes, double quotes, single quotes
+	// or brackets, or not at all
+	return regexp.MustCompile("^(?i:CONSTRAINT)\\s+[\"'`\\[]?" + regexp.QuoteMeta(name) + "[\"'`\\]\\s]")
 }
 
 func (d *ddl) addConstraint(name string, sql string) {
@@ -282,7 +284,7 @@ func (d *ddl) getColumns() []string {
 }
 
 func (d *ddl) removeColumn(name string) bool {
-	reg := regexp.MustCompile("^(`|'|\"| )" + regexp.QuoteMeta(name) + "(`|'|\"| ) .*?$")
+	reg := regexp.MustCompile("^[`'\" ]?" + regexp.QuoteMeta(name) + "[`'\" ]")
 
 	for i := 0; i < len(d.fields); i++ {
 		if reg.MatchString(d.fields[i]) {
diff --git a/ddlmod_test.go b/ddlmod_test.go
index 7d4e1a2..e13db5a 100644
--- a/ddlmod_test.go
+++ b/ddlmod_test.go
@@ -475,3 +475,43 @@ func TestGetColumns(t *testing.T) {
 		})
 	}
 }
+
+func TestParseDDL_LowercaseUnique(t *testing.T) {
+	d, err := parseDDL("CREATE TABLE `t` (`a` text, unique(`a`))")
+	if err != nil {
+		t.Fatal(err)
+	}
+	found := false
+	for _, c := range d.columns {
+		if c.NameValue.String == "a" {
+			found = true
+			if uniq, _ := c.Unique(); !uniq {
+				t.Error("lowercase table-level unique(...) not recognized")
+			}
+		}
+	}
+	if !found {
+		t.Fatal("column a was not parsed at all")
+	}
+}
+
+func TestConstraintNameQuoting(t *testing.T) {
+	forms := map[string]string{
+		"backquotes":    "CREATE TABLE `t` (`a` integer, CONSTRAINT `chk_a` CHECK (`a` > 0))",
+		"double quotes": `CREATE TABLE "t" ("a" integer, CONSTRAINT "chk_a" CHECK ("a" > 0))`,
+		"brackets":      "CREATE TABLE t (a integer, CONSTRAINT [chk_a] CHECK (a > 0))",
+		"unquoted":      "CREATE TABLE t (a integer, CONSTRAINT chk_a CHECK (a > 0))",
+	}
+	for form, ddlSQL := range forms {
+		d, err := parseDDL(ddlSQL)
+		if err != nil {
+			t.Fatalf("%s: %v", form, err)
+		}
+		if !d.hasConstraint("chk_a") {
+			t.Errorf("%s: constraint chk_a not matched", form)
+		}
+		if d.hasConstraint("chk") {
+			t.Errorf("%s: prefix chk must not match", form)
+		}
+	}
+}
diff --git a/migrator.go b/migrator.go
index ae15d4a..e00dd34 100644
--- a/migrator.go
+++ b/migrator.go
@@ -2,6 +2,7 @@ package sqlite
 
 import (
 	"database/sql"
+	"errors"
 	"fmt"
 	"strings"
 
@@ -52,7 +53,9 @@ func (m Migrator) DropTable(values ...interface{}) error {
 }
 
 func (m Migrator) GetTables() (tableList []string, err error) {
-	return tableList, m.DB.Raw("SELECT name FROM sqlite_master where type=?", "table").Scan(&tableList).Error
+	return tableList, m.DB.Raw(
+		"SELECT name FROM sqlite_master WHERE type = ? AND name NOT LIKE ?", "table", "sqlite_%",
+	).Scan(&tableList).Error
 }
 
 func (m Migrator) HasColumn(value interface{}, name string) bool {
@@ -161,7 +164,9 @@ func (m Migrator) DropColumn(value interface{}, name string) error {
 				name = field.DBName
 			}
 
-			ddl.removeColumn(name)
+			if !ddl.removeColumn(name) {
+				return nil, nil, fmt.Errorf("failed to drop column %v: not found in the DDL of table %v", name, stmt.Table)
+			}
 			return ddl, nil, nil
 		})
 	})
@@ -208,22 +213,26 @@ func (m Migrator) DropConstraint(value interface{}, name string) error {
 }
 
 func (m Migrator) HasConstraint(value interface{}, name string) bool {
-	var count int64
+	var has bool
 	m.RunWithValue(value, func(stmt *gorm.Statement) error {
 		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
 		if constraint != nil {
 			name = constraint.GetName()
 		}
 
-		m.DB.Raw(
-			"SELECT count(*) FROM sqlite_master WHERE type = ? AND tbl_name = ? AND (sql LIKE ? OR sql LIKE ? OR sql LIKE ? OR sql LIKE ? OR sql LIKE ?)",
-			"table", table, `%CONSTRAINT "`+name+`" %`, `%CONSTRAINT `+name+` %`, "%CONSTRAINT `"+name+"`%", "%CONSTRAINT ["+name+"]%", "%CONSTRAINT \t"+name+"\t%",
-		).Row().Scan(&count)
-
+		rawDDL, err := m.getRawDDL(table)
+		if err != nil {
+			return err
+		}
+		parsed, err := parseDDL(rawDDL)
+		if err != nil {
+			return err
+		}
+		has = parsed.hasConstraint(name)
 		return nil
 	})
 
-	return count > 0
+	return has
 }
 
 func (m Migrator) CurrentDatabase() (name string) {
@@ -367,10 +376,13 @@ func (m Migrator) GetIndexes(value interface{}) ([]gorm.Index, error) {
 
 func (m Migrator) getRawDDL(table string) (string, error) {
 	var createSQL string
-	m.DB.Raw("SELECT sql FROM sqlite_master WHERE type = ? AND tbl_name = ? AND name = ?", "table", table, table).Row().Scan(&createSQL)
+	err := m.DB.Raw("SELECT sql FROM sqlite_master WHERE type = ? AND tbl_name = ? AND name = ?", "table", table, table).Row().Scan(&createSQL)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return "", err
+	}
 
-	if m.DB.Error != nil {
-		return "", m.DB.Error
+	if createSQL == "" {
+		return "", fmt.Errorf("failed to get DDL of table %q: table not found", table)
 	}
 	return createSQL, nil
 }
diff --git a/migrator_test.go b/migrator_test.go
index 301d3bc..6cf4e8f 100644
--- a/migrator_test.go
+++ b/migrator_test.go
@@ -178,3 +178,101 @@ func openRecreateTestDB(t *testing.T, name string) *gorm.DB {
 	})
 	return db
 }
+
+// GetTables must not report SQLite internal tables such as sqlite_sequence,
+// which appears as soon as any table uses AUTOINCREMENT.
+func TestGetTablesExcludesInternal(t *testing.T) {
+	db, err := gorm.Open(Open("file:internal_tables?mode=memory&cache=shared"), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("gorm.Open: %v", err)
+	}
+	t.Cleanup(func() {
+		if sqlDB, err := db.DB(); err == nil {
+			_ = sqlDB.Close()
+		}
+	})
+
+	if err := db.Exec("CREATE TABLE `seq_table` (`id` integer PRIMARY KEY AUTOINCREMENT)").Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Exec("INSERT INTO `seq_table` DEFAULT VALUES").Error; err != nil {
+		t.Fatal(err)
+	}
+
+	tables, err := db.Migrator().GetTables()
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, tb := range tables {
+		if strings.HasPrefix(tb, "sqlite_") {
+			t.Errorf("GetTables returned internal table %q", tb)
+		}
+	}
+	if len(tables) != 1 || tables[0] != "seq_table" {
+		t.Errorf("GetTables = %v, want [seq_table]", tables)
+	}
+}
+
+type checkedModel struct {
+	ID  int
+	Age int `gorm:"check:age_positive,age > 0"`
+}
+
+func (checkedModel) TableName() string { return "checked_models" }
+
+// HasConstraint must match the exact constraint name instead of a LIKE
+// substring, and DropColumn must fail for a column that is not in the DDL
+// instead of silently rebuilding an identical table.
+func TestConstraintAndColumnMatching(t *testing.T) {
+	db, err := gorm.Open(Open("file:constraint_matching?mode=memory&cache=shared"), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("gorm.Open: %v", err)
+	}
+	t.Cleanup(func() {
+		if sqlDB, err := db.DB(); err == nil {
+			_ = sqlDB.Close()
+		}
+	})
+
+	if err := db.AutoMigrate(&checkedModel{}); err != nil {
+		t.Fatal(err)
+	}
+	if !db.Migrator().HasConstraint(&checkedModel{}, "age_positive") {
+		t.Error("HasConstraint(age_positive) = false, want true")
+	}
+	if db.Migrator().HasConstraint(&checkedModel{}, "age_pos") {
+		t.Error("HasConstraint(age_pos) matched by prefix, want false")
+	}
+
+	// unquoted DDL: the column must still be dropped
+	if err := db.Exec("CREATE TABLE plain_cols (id integer, name text)").Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Migrator().DropColumn(&plainColModel{}, "name"); err != nil {
+		t.Fatalf("DropColumn on unquoted DDL: %v", err)
+	}
+	if db.Migrator().HasColumn(&plainColModel{}, "name") {
+		t.Error("column still present after DropColumn on unquoted DDL")
+	}
+	// a missing column must be an error, not a silent no-op
+	if err := db.Migrator().DropColumn(&plainColModel{}, "missing"); err == nil {
+		t.Error("DropColumn(missing) = nil, want error")
+	}
+	// a missing table must be reported clearly
+	if err := db.Migrator().DropColumn(&noSuchTableModel{}, "col"); err == nil || !strings.Contains(err.Error(), "table not found") {
+		t.Errorf("DropColumn on a missing table = %v, want a table-not-found error", err)
+	}
+}
+
+type plainColModel struct {
+	ID   int
+	Name string
+}
+
+func (plainColModel) TableName() string { return "plain_cols" }
+
+type noSuchTableModel struct {
+	ID int
+}
+
+func (noSuchTableModel) TableName() string { return "no_such_table" }