怎么对mysql的内容进行条件查询
"select id from biao where a='A'" //精确查找
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"select id from biao where a LIKE '%A%'" //模糊查找
mysql如何判断符合查询条件的数据有两条
mysql判断符合查询条件的数据有两条根据查询相关资料：
1、查询数据库表数据，根据指定条件筛选出满足条件的数据，此例返回满足条件的两条数据。
2、关键字查询，使用AND搜索栏输入符合条件的数据。
C#连接mysql数据库如何实现多条件查询
给你一个稍微复杂一点的查询，我设计的
看上图我把第一列标签后面的控件命名有规律，比如计划工厂后面文本框是"计划工厂t"，Exapt命名为"计划工厂c"，后面还隐藏一个listbox，命名为"计划工厂l"。
计划工厂 这个名称本身就是我要查询的表里面包含的字段。
利用这种界面，我要完成一些复杂点的查询：点文本框里的小图标按钮，弹出工具，可以输入多条件，条件可以成立为模糊条件（用*代替不认识部分），也可以成立为否决条件。
选中Exapt全部否定所成立条件；点击执行按钮，有条件的成立条件，无条件的不成立。
所以这种东西贯穿软件我就不能每个都去做，就只能写一个类文件：
public class conditionset
{
public void load_condit(Panel p)
{
foreach (Control ctl in p.Controls)
{
if (ctl is SkinTextBox)
{
SkinTextBox sktxt = (SkinTextBox)p.Controls[ctl.Name];
ListBox list = (ListBox)p.Controls[sktxt.Name.Substring(0, sktxt.Name.Length - 1) + "l"];
sktxt.IconClick += (Object sen, EventArgs ed) =
{
ctl.condition toolform = new ctl.condition();
if (list.Items.Count 0)
{
sktxt.Text = "┅";
sktxt.ReadOnly = true;
}
foreach (var sm in list.Items)
{
toolform.dv.Rows.Add(sm.ToString());
}
toolform.Show();
toolform.cleari += (Object send, EventArgs er) =
{
sktxt.Text = "";
sktxt.ReadOnly = false;
};
toolform.subm += (Object send, EventArgs er) =
{
list.Items.Clear();
foreach (DataGridViewRow dvr in toolform.dv.Rows)
{
if (Convert.ToString(dvr.Cells[0].Value) != "")
{
list.Items.Add(Convert.ToString(dvr.Cells[0].Value));
}
}
sktxt.Text = "┅";
sktxt.ReadOnly = true;
};
};
}
}
}
public string condit(Panel p)
{
string master_condition = "";
foreach (Control ctl in p.Controls)
{
//遍历panel查找条件
#region
string condition = "";
if (ctl is SkinTextBox)
{
//文本框条件组合
#region
SkinTextBox sktxt = (SkinTextBox)p.Controls[ctl.Name];
string ziduan_name = sktxt.Name.Substring(0, sktxt.Name.Length - 1);
SkinCheckBox skck = (SkinCheckBox)p.Controls[ctl.Name.Substring(0, ctl.Name.Length - 1) + "c"];
ListBox list = (ListBox)p.Controls[ctl.Name.Substring(0, ctl.Name.Length - 1) + "l"];
if (sktxt.Text != "")
{
if (sktxt.Text == "┅")
{
string blur_str = "", blur = "";
foreach (var itm in list.Items)
{
if (itm.ToString().Contains("*"))
{
if (skck.Checked == true)
{
blur += " and " + ziduan_name + " not like '" + itm.ToString().Replace("*", "%") + "'";
}
else
{
blur += " or " + ziduan_name + " like '" + itm.ToString().Replace("*", "%") + "'";
}
}
else
{
blur_str += "'" + Convert.ToString(itm) + "',";
}
}
string blur_sql = (blur == "") ? "" : blur.Substring(4, blur.Length - 4).Trim();
string in_condition = "", like_condition = "";
if (skck.Checked == true)
{
in_condition = ziduan_name + " not in ";
like_condition = " and ";
}
else
{
in_condition = ziduan_name + " in ";
like_condition = " or ";
}
string contains_sql = (blur_str == "") ? "" : in_condition + "(" + blur_str.Substring(0, blur_str.Length - 1) + ")";
condition = contains_sql + blur_sql;
if (blur_sql != "" contains_sql != "")
{
condition = contains_sql + like_condition + blur_sql;
}
else
{
condition = contains_sql + blur_sql;
}
}
else
{
if (!sktxt.Text.Contains("*"))
{
if (skck.Checked == true)
{
condition = ziduan_name + "'" + sktxt.Text + "'";
}
else
{
condition = ziduan_name + "='" + sktxt.Text + "'";
}
}
else
{
if (skck.Checked == true)
{
condition = ziduan_name + " not like '" + sktxt.Text.Replace("*", "%") + "'";
}
else
{
condition = ziduan_name + " like '" + sktxt.Text.Replace("*", "%") + "'";
}
}
}
}
#endregion
}
if (ctl is SkinDateTimePicker)
{
//日期条件组合
#region
if (ctl.Name.Substring(ctl.Name.Length - 1, 1) != "t")
{
SkinDateTimePicker skdate_sta = (SkinDateTimePicker)p.Controls[ctl.Name];
SkinDateTimePicker skdate_end = (SkinDateTimePicker)p.Controls[ctl.Name + "t"];
if (skdate_sta.text != "")
{
if (skdate_end.text == "")
{
condition = skdate_sta.Name + "='" + skdate_sta.text + "'";
}
else
{
condition = skdate_sta.Name + "='" + skdate_sta.text + "' and " + skdate_sta.Name + "='" + skdate_end.text + "'";
}
}
}
#endregion
}
master_condition += (condition == "") ? "" : "(" + condition + ") and ";
#endregion //遍历panel查找条件
}
string condition_sql = (master_condition == "") ? "" : master_condition.Substring(0, master_condition.Length - 5);
return condition_sql;
}
}
工具用一个窗体代替：
public partial class condition : Form
{
public condition()
{
InitializeComponent();
}
public event EventHandler subm;
public event EventHandler cleari;
private void submit_Click(object sender, EventArgs e)
{
subm(sender, e);
this.Dispose();
}
private void clearit_Click(object sender, EventArgs e)
{
this.Dispose();
dv.Rows.Clear();
cleari(sender, e);
}
}
当我们执行多条件的时候就等于拼接条件
mysql 条件查询
IFNULL 函数即可
SELECT
*
FROM
db_staff AS user
WHERE
user.id = IFNULL(id, user.id)
AND user.`name` = IFNULL(name, user.`name` )
AND user.role = IFNULL(role, user.role)
也就是 如果参数 id 是 null，
那么
user.id = IFNULL(id, user.id)
就相当于
user.id = user.id
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