db.Statement.SQL.Grow(180)
			db.Statement.AddClauseIfNotExists(clause.Update{})
			if _, ok := db.Statement.Clauses["SET"]; !ok {
				if set := ConvertToAssignments(db.Statement); len(set) != 0 {
					defer delete(db.Statement.Clauses, "SET")
					db.Statement.AddClause(set)
				} else {
					return
				}
			}

			db.Statement.Build(db.Statement.BuildClauses...)
		}

		checkMissingWhereConditions(db)

func (constraint *Constraint) Build() (sql string, vars []interface{}) {
	sql = "CONSTRAINT ? FOREIGN KEY ? REFERENCES ??"
	if constraint.OnDelete != "" {
		sql += " ON DELETE " + constraint.OnDelete
	}

	if constraint.OnUpdate != "" {
		sql += " ON UPDATE " + constraint.OnUpdate
	}

	foreignKeys := make([]interface{}, 0, len(constraint.ForeignKeys))