Let
How do I use Let
Below are practical examples compiled from projects for learning and reference purposes
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File name: ClassBLL.cs
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83 public DataTable XemDiemLop(string MaLop)
84 {
85 SqlConnection con = new SqlConnection();
86 ChuanBi3Table();
87 string sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
88 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
89 " where MaLop='" + MaLop + "'";
90 DataTable dt4 = da.GetTable(sql4);
91 da.ExcuteNonQuery("delete from Loptc where MaSV in ( select MaSV from Loptc )");
92 da.ExcuteNonQuery("delete from Lopdiem10 where MaSV in ( select MaSV from Lopdiem10 )");
93 da.ExcuteNonQuery("delete from DTB where MaSV in ( select MaSV from DTB )");
94 return dt4;
95 }
File name: ClassBLL.cs
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96 public DataTable ThongKeLop(string MaHK,string MaLop,int loai)
97 {
98 SqlConnection con = da.GetConnect();
99 ChuanBi3Table(MaHK);
100 //Truy van cuoi cung
101 string sql4;
102 switch (loai)
103 {
104 case 0:
105 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
106 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
107 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 >= 9";
108 break;
109 case 1:
110 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
111 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
112 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 >=8 and TrungBinhCuoiKyHe10 < 9";
113 break;
114 case 2:
115 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
116 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
117 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 >=6.5 and TrungBinhCuoiKyHe10 < 8";
118 break;
119 case 3:
120 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
121 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
122 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 >=5 and TrungBinhCuoiKyHe10 < 6.5";
123 break;
124 case 4:
125 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
126 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
127 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 >=3.5 and TrungBinhCuoiKyHe10 < 5";
128 break;
129 default:
130 sql4 = "select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 " +
131 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV " +
132 " where MaLop='" + MaLop + "' and TrungBinhCuoiKyHe10 < 3.5";
133 break;
134 }
135 DataTable dt4 = da.GetTable(sql4);
136 da.ExcuteNonQuery("delete from Loptc where MaSV in ( select MaSV from Loptc )");
137 da.ExcuteNonQuery("delete from Lopdiem10 where MaSV in ( select MaSV from Lopdiem10 )");
138 da.ExcuteNonQuery("delete from DTB where MaSV in ( select MaSV from DTB )");
139 return dt4;
140 }
File name: ClassBLL.cs
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141 public DataTable ThongKeKhoiLop(string MaHK, string MaKhoiLop, int loai)
142 {
143 SqlConnection con = da.GetConnect();
144 ChuanBi3Table(MaHK);
145 string sql4;
146 switch (loai)
147 {
148 case 0:
149 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
150 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
151 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
152 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 >=9 ";
153 break;
154 case 1:
155 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
156 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
157 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
158 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 >=8 and TrungBinhCuoiKyHe10 < 9";
159 break;
160 case 2:
161 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
162 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
163 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
164 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 >=6.5 and TrungBinhCuoiKyHe10 < 8";
165 break;
166 case 3:
167 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
168 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
169 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
170 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 >=5 and TrungBinhCuoiKyHe10 < 6.5";
171 break;
172 case 4:
173 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
174 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
175 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
176 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 >=3.5 and TrungBinhCuoiKyHe10 < 5";
177 break;
178 default:
179 sql4 = "select sv.MaSV,TenSV,sv.MaLop,TrungBinhCuoiKyHe10 " +
180 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV,KhoiLop kl,Lop l " +
181 " where sv.MaLop=l.MaLop and l.MaKhoiLop=kl.MaKhoiLop " +
182 " and kl.MaKhoiLop='" + MaKhoiLop + "' and TrungBinhCuoiKyHe10 < 3.5";
183 break;
184 }
185 DataTable dt4 = da.GetTable(sql4);
186 da.ExcuteNonQuery("delete from Loptc where MaSV in ( select MaSV from Loptc )");
187 da.ExcuteNonQuery("delete from Lopdiem10 where MaSV in ( select MaSV from Lopdiem10 )");
188 da.ExcuteNonQuery("delete from DTB where MaSV in ( select MaSV from DTB )");
189 return dt4;
190 }
File name: ClassBLL.cs
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289 public DataTable XemDiemLop(string MaHK,string MaLop)
290 {
291 SqlConnection con = new SqlConnection();
292 ChuanBi3Table(MaHK);
293 string sql4="select sv.MaSV,TenSV,TrungBinhCuoiKyHe10 "+
294 " from DTB left join SinhVien sv on DTB.MaSV=sv.MaSV "+
295 " where MaLop='"+MaLop+"'";
296 DataTable dt4 = da.GetTable(sql4);
297 da.ExcuteNonQuery("delete from Loptc where MaSV in ( select MaSV from Loptc )");
298 da.ExcuteNonQuery("delete from Lopdiem10 where MaSV in ( select MaSV from Lopdiem10 )");
299 da.ExcuteNonQuery("delete from DTB where MaSV in ( select MaSV from DTB )");
300 return dt4;
301 }
File name: ClassBLL.cs
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312 public void Delete(string table, string sql)
313 {
314 sql = "delete from "+table+" where "+sql+"";
315 da.ExcuteNonQuery(sql);
316 }
File name: FormGiangVien.cs
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57 private void btnXoa_Click(object sender, EventArgs e)
58 {
59 DialogResult result;
60 result = MessageBox.Show("Bạn có chắc chắn muốn xóa không ?","Hệ Thống", MessageBoxButtons.YesNo);
61 if (result == DialogResult.Yes)
62 {
63 string sql = "MaGV='" + txtMaGV.Text + "'";
64 business.Delete("GiangVien", sql);
65 FormGiangVien_Load(sender, e);
66 }
67 }
File name: FormHeDaoTao.cs
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54 private void btnXoa_Click(object sender, EventArgs e)
55 {
56 DialogResult result;
57 result = MessageBox.Show("Bạn có chắc chắn muốn xóa không ?","Hệ Thống", MessageBoxButtons.YesNo);
58 if (result == DialogResult.Yes)
59 {
60 string sql = "MaHeDT = '" + txtMaHeDT.Text + "'";
61 business.Delete("HeDaoTao", sql);
62 FormHeDaoTao_Load(sender, e);
63 }
64 }
File name: FormHocKy.cs
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40 private void btnXoa_Click(object sender, EventArgs e)
41 {
42 DialogResult result;
43 result = MessageBox.Show("Bạn có chắc chắn muốn xóa không ?","Hệ Thống", MessageBoxButtons.YesNo);
44 if (result == DialogResult.Yes)
45 {
46 string sql = "MaHK='" + txtMaHocKy.Text + "'";
47 business.Delete("HocKy", sql);
48 FormHocKy_Load(sender, e);
49 }
50 }
File name: FormHocPhan.cs
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41 private void btnXoa_Click(object sender, EventArgs e)
42 {
43 DialogResult result;
44 result = MessageBox.Show("Bạn có chắc chắn muốn xóa không ?","Hệ Thống", MessageBoxButtons.YesNo);
45 if (result == DialogResult.Yes)
46 {
47 string sql = "MaHP='" + txtMaHP.Text + "'";
48 business.Delete("HocPhan", sql);
49 FormHocPhan_Load(sender, e);
50 }
51 }
File name: FormKHGD.cs
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51 private void btnXoa_Click(object sender, EventArgs e)
52 {
53 DialogResult result;
54 result = MessageBox.Show("Bạn có chắc chắn muốn xóa không ?", "Hệ Thống", MessageBoxButtons.YesNo);
55 if (result == DialogResult.Yes)
56 {
57 string sql = "MaKHGD='" + txtMaKHGD.Text + "'";
58 business.Delete("KeHoachGiangDay", sql);
59 FormKHGD_Load(sender, e);
60 }
61 }
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