DataTable中Compute计算函数  1 DataTable dt = new DataTable();
2//嵌套的三元运算⽜叉到五体投地
3object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);
4 Response.Write(obj);
5
6
7 System.Data.DataTable table = new DataTable();
8//计算常量，可以没有初始化列
9object test = table.Compute("1+1", "");
writeline函数10 Console.WriteLine(test);
11
12string a = "123";
13 System.Double b = 123;
14decimal c = 123m;
15 Console.WriteLine(Convert.ToDecimal(a));
16//test=2;
17
18 test = table.Compute("1+1", "false");
19 Console.WriteLine(test);
20//test=2；常数计算和filter⽆关
21
22 test = table.Compute("abs(1)", "");
23 Console.WriteLine(test);
24//test=null，不知道为这个什么没有报错，⽽且返回null，其他的数学函数都会抱错
25
26 test = table.Compute("2%2", "");
27 Console.WriteLine(test);
28//test=0;
29//其他函数参考下⾯的计算列
30
31
32
33//初始化datatale
34 table.Columns.Add("id", typeof(string));
35 table.Columns.Add("value", typeof(int));
36for (int i = 1; i <= 10; i++)
37 {
38 System.Data.DataRow dRow = table.NewRow();
39 dRow["id"] = "id" + i.ToString();
40 dRow["value"] = i;
41 table.Rows.Add(dRow);
42 }
43
44
45
46//test = table.Compute("value+1", "true");
47/**/
48////抛出异常，这⾥必须是聚合函数
49
50
51
52//*************************************⽀持的聚合函数**********************//
53
54//求数量
55 test = table.Compute("count(id)", "false");
56 Console.WriteLine(test);
57//test=0;
58
59 test = table.Compute("count(id)", "true");
60 Console.WriteLine(test);
61//test=10;
62
63
64
65//求和
66 test = table.Compute("sum(value)", "");
67 Console.WriteLine(test);
68//test=55;
69
70//test = table.Compute("sum(id)","");
71/**/
72////抛出异常，这⾥不能是string
73
74
75//平均
76 test = table.Compute("avg(value)", "");
77 Console.WriteLine(test);
78//test=5;
79
80
81//最⼩
82 test = table.Compute("min(value)", "");
83 Console.WriteLine(test);
84//test=1;
85
86//最⼤
87 test = table.Compute("max(value)", "");
88 Console.WriteLine(test);
89//test=10;
90
91//统计标准偏差
92 test = table.Compute("StDev(value)", "");
93 Console.WriteLine(test);
94//test=3.02765035409749
95
96//统计⽅差
97 test = table.Compute("Var(value)", "");
98 Console.WriteLine(test);
99//test=9.16666666666667
100
101
102//复杂计算
103 test = table.Compute("max(value)/sum(value)", "");
104 Console.WriteLine(test);
105//test=0.181818181818182
106
107/**/
108/*******************************************计算列*************************/
109
110 System.Data.DataColumn column = new DataColumn("exp1", typeof(float)); 111 table.Columns.Add(column);
112
113
114//简单计算
115 column.Expression = "value*2";
116 test = table.Select("id='id1'")[0]["exp1"];
117 Console.WriteLine(test);
118//test=2;
119
120//字符串函数
121 column.Expression = "len(id)";
122 test = table.Select("id='id1'")[0]["exp1"];
123 Console.WriteLine(test);
124//test=3;
125
126//字符串函数
127 column.Expression = "len(' '+id+' ')";
128 test = table.Select("id='id1'")[0]["exp1"];
129 Console.WriteLine(test);
130//test=5;
131
132//字符串函数
133 column.Expression = "len(trim(' '+id+' '))";
134 test = table.Select("id='id1'")[0]["exp1"];
135 Console.WriteLine(test);
136//test=3;
137
138//字符串函数
139 column.Expression = "substring(id,3,len(id)-2)";
140 test = table.Select("id='id1'")[0]["exp1"];
141 Console.WriteLine(test);
142//test=1; //substring的起始字符位置为1不是0
143
144//类型转换
145 column.Expression = "convert(substring(id,3,len(id)-2),'System.Int32')*1.6"; 146 test = table.Select("id='id1'")[0]["exp1"];
147 Console.WriteLine(test);
148//test=1.6;
149
150//相当于sqlserver的isnull
151 column.Expression = "isnull(value,10)";
152 test = table.Select("id='id1'")[0]["exp1"];
153 Console.WriteLine(test);
154//test=1;
155
156//三元运算符，相当于sqlserver的case when
157 column.Expression = "iif(value>5,1000,2000)";
158 test = table.Select("id='id1'")[0]["exp1"];
159 Console.WriteLine(test);
160//test=2000;
161
162//like运算符
163 column.Expression = "iif(id like '%1',1000,2000)";
164 test = table.Select("id='id1'")[0]["exp1"];
165 Console.WriteLine(test);
166//test=1000;
167
168//in运算符
169 column.Expression = "iif(id not in('id1'),1000,2000)";
170 test = table.Select("id='id1'")[0]["exp1"];
171 Console.WriteLine(test);
172//test=2000;
173
174//嵌套的三元运算
175 column.Expression = "iif(value>5,1000,iif(id like '%1',4000,2000))";
176 test = table.Select("id='id1'")[0]["exp1"];
177 Console.WriteLine(test);
178//test=4000;
179
180
181//客户端计算所占总数的百分⽐
182 column.Expression = "value/sum(value)";
183 test = table.Select("id='id1'")[0]["exp1"];
184 Console.WriteLine(test);
185//test=0.01818182
186
187
188//客户端计算差值,⽐如nba常规赛的胜场差
189 column.Expression = "max(value)-value";
190 test = table.Select("id='id1'")[0]["exp1"];
191 Console.WriteLine(test);
192//test=9
193
194
195//***********************⽗⼦表计算*************************************/
196
197
198//初始化⼦表,⽗⼦表关系
199 DataTable tableChild = new DataTable();
200
201 tableChild.Columns.Add("id", typeof(string));
202 tableChild.Columns.Add("value", typeof(int));
203
204 System.Data.DataSet ds = new DataSet();
205 ds.Tables.Add(tableChild);
206 ds.Tables.Add(table);
207 DataRelation relation = new DataRelation("relation", table.Columns["id"], tableChild.Columns["id"]); 208 ds.Relations.Add(relation);
209
210for (int i = 1; i <= 10; i++)
211 {
212 System.Data.DataRow dRow = tableChild.NewRow();
213 dRow["id"] = "id1";
214 dRow["value"] = i;
215 tableChild.Rows.Add(dRow);
216 }
217
218
219//计算⼦表记录数
220 column.Expression = "count(child(relation).value)";
221 test = table.Select("id='id1'")[0]["exp1"];
222 Console.WriteLine(test);
223//test=10;
224
225
226
227//计算⽗⼦表的百分⽐
228 column.Expression = "value/sum(child(relation).value)";
229 test = table.Select("id='id1'")[0]["exp1"];
230 Console.WriteLine(test);
231//test=0.01818182;
232
233
234//计算⽗⼦表的差值,⽐如⽗表为库存数量，⼦表为订购数量，计算得出需要补充的数量
235 column.Expression = "iif(value-sum(child(relation).value)>0,0,value-sum(child(relation).value))"; 236 test = table.Select("id='id1'")[0]["exp1"];
237 Console.WriteLine(test);
238//test=-54;
239
240//⽐较遗憾的是没有发现能够计算同⽐和环⽐的⽅法，⽽且计算列⽆法作为约束
241//结束，DataTable可以让你尽量发挥聪明才智来减少繁杂的sql语句并且减轻服务器计算符合

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