Sql动态查询拼接字符串的优化

Sql动态查询拼接字符串的优化

 

最原始的 直接写：string sql="select * from TestTables where 1=1";

... 这样的代码效率很低的，这样影响了数据库的索引引用

如下所示：

private void TestOneMethod()

        { 

            string querySql = "select * from TestTables where 1=1";

            if (hasOneCondition)

            {

                querySql += "oneCondition='oneCondition'";

            }

            if (hasTwoCondition)

            {

                querySql += "twoCondition='twoCondition'";

            }

            if (hasThreeCondition)

            {

                querySql +=  "threeCondition='threeCondition'";

            }

            // ....其他条件

            // ExcSql(querySql)

        }

优化方案A：

去掉 string sql="where 1=1"

那么，在用的时候定义一个变量，用来标志是否应存在了hasWhere=false ，如果已经存在了则 hasWhere=!hasWhere.这样下一次在用的时候就

可以用下面的形式表示了:

private void TestOneMethod()

        { 

            string querySql = "select * from TestTables";

            bool _hasWhere = false;

            if (hasOneCondition)

            {

                querySql += _hasWhere ? "where" : "and" + "oneCondition='oneCondition'";

                _hasWhere = true;

            }

            if (hasTwoCondition)

            {

                querySql += _hasWhere ? "where" : "and" + "twoCondition='twoCondition'";

                _hasWhere = true;

            }

            if (hasThreeCondition)

            {

                querySql += _hasWhere ? "where" : "and" + "threeCondition='threeCondition'";

                _hasWhere = true;

            }

            // ....其他条件

            // ExcSql(querySql)

        }

....

经过优化后，sql的效率提高了，但是仍然存在问题，问题在哪里呢？如果我们每次都这样写的话是不是非常的费力，那么就提出一个通用的方

法，这个通用的方法首先得有一个bool类型的返回值，用来确认当前是否需要hasString。如下，在应用的时候：

private bool SeachHelper(string whereString, bool hasWhere)

        {

            if (!hasWhere)

                whereString = "where" + whereString;

            else

                whereString = "and" + whereString;

            return true;

        }

private void TestTwoMethod()

        {

            string querySql = "select * from TestTables";

            bool _hasWhere = false;

            if (hasOneCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql += "oneCondition='oneCondition'";

            }

            if (hasThreeCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql += "twoCondition='twoCondition'";

            }

            if (hasThreeCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql += "threeCondition='threeCondition'";

            }

            // ....其他条件

            // ExcSql(querySql);

        }

代码简洁了不少，但是仍然粗只能问题，那么问题又是什么呢？

额，字符串来回的拼接非常的浪费资源，那么 ，用StringBuilder啊，好接下来继续。

 private void TestThreeMethod()

        {

            StringBuilder querySql = new StringBuilder();

            querySql.Append("select * from TestTables");

            bool _hasWhere = false;

            if (hasOneCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql.Append("oneCondition='oneCondition'");

            }

            if (hasThreeCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql.Append("twoCondition='twoCondition'");

            }

            if (hasThreeCondition)

            {

                _hasWhere = SeachHelper(querySql, _hasWhere);

                querySql.Append("threeCondition='threeCondition'");

            }

            // ....其他条件

            // ExcSql(querySql.ToString());