c#子查询不起作用

Question

I like to add subquery to mysql database, but it gives me error.

string q = "INSERT INTO table1(isbn,date,ID,title) 
values('" + this.textBoxisbn.Text + "','" + this.dateTimePicker1.Value.ToString("yyyy-MM-dd") + "','" + this.textBoxk.Text + "'(select title from books where isbn=" + textBox1.Text + "')'" + "');";

Answer 1

You are missing a comma. Add +","+ before your sub-query.

string q = "INSERT INTO table1(isbn,date,ID,title) 
values('" + this.textBoxisbn.Text + "','" + 
this.dateTimePicker1.Value.ToString("yyyy-MM-dd") + "','" + 
this.textBoxk.Text + "','" + "'(select title from books 
where isbn=" + textBox1.Text + "')'" + "');";

Tip : It would be better to use placeholders in your query along with prepared statements rather than doing this ('" + this.textBoxisbn.Text + "','"...

Answer 2

Make the query readable with a help of verbatim strings and string interpolation :

   string q = 
     $@"INSERT INTO table1(
          Isbn,
          Date,
          ID,
          Title) 
        VALUES(
          '{textBoxisbn.Text}',
          '{dateTimePicker1.Value.ToString("yyyy-MM-dd")}',
          '{textBoxk.Text}',
          (SELECT Title
             FROM Books
            WHERE Isbn = '{textBox1.Text}'))";

and you'll easily find out all syntax errors in the query. Further improvement is changing the query into parametrized one:

   string q = 
     $@"INSERT INTO table1(
          Isbn,
          Date,
          ID,
          Title) 
        VALUES(
          @prm_Isbn,
          @prm_Date,
          @prm_Id,
          (SELECT Title
             FROM Books
            WHERE Isbn = @prm_IsbnForTitle))";