I have following code for deleting a value from database:

a=get(handles.edit1,'String');

a=convertCharsToStrings(a);

sql=['delete from student where usn=''',a]

curs=fetch(conn,sqlquery);

[Walter Roberson]

User's tag says,

this code gives error for value of a='4cs012' as: expected input to be string scalar or character vector

Answer 1

[Walter Roberson]

You converted a to string data type. When you use [character_vector, string_object] then it converts the character vector to a string object and then forms the nonscalar string array, which is not valid for conn.

Either do not convert a to string object or else use string concatenation which is the + operation

'delete from etc' + a

By the way, you are more likely to be successful if you remember the " character that is needed to terminate the command that is sent, to match the one just before you drop in the variable.

[Athfin I]

That again gives error as unknown column '4cs012'.

[Guillaume]

At this point, the problem is nothing to do with matlab. You need to learn to write valid SQL queries. In particular, in SQL string literals needs to be enclosed in single or double quotes. The error message you get is entirely correct, if 4cs012 is not enclosed in quotes in the query, then it is interpreted as a column name.

SQL statements also need to be terminated with a semicolon.

Probably the easiest way to build your query is with:

sql = sprintf('delete from student where usn = "%s";', a);

<rant> The biggest problem with your code is that it's open to SQL injection. I don't understand why people are stll taught to build SQL queries that depend on user input this way instead of using prepared statements which are not vulnerable to SQL injection. If a user enters "; drop table student;-- in your edit control, they will have deleted your table. (famous XKCD published 12 years ago, and people still do it!) </rant over>

[Athfin I]

Thanks a lot. That worked for me, but semicolumn wasn't necessary.