MATLAB: How to run large SQL statements on new lines

sql variable

Good afternoon all…

Little questions regarding SQL statements in Matlab. I am currently using 2018 version and have produced a script that connects to a database and extracts data using a simple SQL statement.

I am trying to understand how you can tidy up the script by using larger SQL queries to extract more data by using a new line e.g …

if true
  % %Open the connection string- connect to Database
conn.Open(connection_string1);
SQL = 'select table.leg_no', ...
     'from table');
end

This will only work if I place the whole statement on one line. I have tried [] and ().

Eventually I would like to create larger SQL queries that can be stored into variables to use in a GUI.

Really appreciate some help with this..Many thanks 🙂

Please note: I am not running with the DataBase Toolbox.

Best Answer

Your question is really about how to input a char vector using more than one line:

SQL = ['select table.leg_no ', ...
       'from table ', ...
       'where table.col1 = 12345'];

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MATLAB: Do i receive the error ‘Too many output arguments’ when using sqlite/exec command

Hi Markus, I ran your code on my own SQLite database and got the same error as you did and noticed something curious that is not entirely clear on the SQLite or exec documentation pages. In the Exec documentation page

https://www-integ3.mathworks.com/help/releases/R2018a/database/ug/exec.html?searchHighlight=exec&s_tid=doc_srchtitle

it says the following

“exec(conn,sqlquery) performs database operations on a SQLite database file by executing the SQL statement sqlquery for the SQLite connection conn using the MATLAB® interface to SQLite.”

However it does not mention SQLite in the examples below where it sets the result of exec to the variable curs. I set up another connection to a database and it looks like the SQLite connection is a different type of object than a normal database connection object in MATLAB. It doesn’t look like it is possible to set the value of exec to be a cursor object for a SQLite connection made using the sqlite function, however you should be able to get a proper connection object if you instead establish the connection with the JDBC driver and database function.

https://www.mathworks.com/help/database/ug/sqlite-jdbc-windows.html#bt8kopk-3

You can interface with it from the command line as they show at the bottom of the doc page and this object should let you assign the result of exec to be a cursor object.

MATLAB: How can i execute query with charachter condition with database toolbox R2011b

Yasser - if I build the same SQL string using your code, then the string becomes

 select LINGUSTIC_NAME from METAKNOWLEDGE_DETwhere FIELD_NAME = 'AGE'

Note how there is no space between the table name and the where condition. Try re-creating your SQL command as

 sql_age = ['select LINGUSTIC_NAME from METAKNOWLEDGE_DET ' ... 
            'where FIELD_NAME = ' '''AGE'''];

Best Answer

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MATLAB: Do i receive the error ‘Too many output arguments’ when using sqlite/exec command

MATLAB: How can i execute query with charachter condition with database toolbox R2011b

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