批处理执行的SQL语句可更新两个表

Question

I have a problem which seems difficult for me, I have a table Category and a table Questions(this table has category_id field with default 0), On my form I can select a category from combobox and my question to you, how can I Insert/Update to a table a new question to a ready made category? My code so far Only adds a new question with a 0 as category, not the one from combobox (combobox displays only text)

String SQL2 = "UPDATE gamequestions SET question_id='gamecategory.category_name =" +jComboBox1.getSelectedItem().toString()+" ,gamequestions.category_id = gamecategory.category_id' WHERE question_id='0' ;"; stmt.addBatch(SQL2);

This is the updated code

"INSERT INTO gamequestions (question_id, category_id, question) SELECT NULL as question_id ,c.category_id, q.question='"+jTextArea1.getText()+"' FROM gamecategory c, gamequestions q WHERE  c.category_name = '"+Combo_click+"' ORDER BY c.category_id LIMIT 1"

And I cant figure out how to make jtextarea fill a column question.

Answer 1

I can't figure out what your code is supposed to be doing.

You say you want to either INSERT a new row with a specified value for category_id column (something other than a hard coded zero), or you want to UPDATE an existing row to change the value of the category_id column.

Let's start with the SQL text that would needs to be sent to the database.

To change an existing row, for example:

UPDATE gamequestions q
   SET q.category_id = 2 
 WHERE q.question_id = 42

To insert a new row (assuming question_id is auto_increment) for example:

INSERT INTO gamequestions (question_id, category_id) VALUES (NULL, 2)

The value returned from the combobox selection would replace the '2' in the example above.

If your combobox isn't returning the category_id value, but is returning the value of some other column from the gamecategory table, and you want the SQL statement to do a "lookup" of the category_id value from the gamecategory table using the category_name value, one way to do that is a subquery as the value being assigned to the column...:

UPDATE gamequestions q
   SET q.category_id = (SELECT c.category_id 
                          FROM gamecategory c
                         WHERE c.category_name = ?
                         ORDER BY c.category_id
                         LIMIT 1
                       )
 WHERE q.question_id = 42

For an INSERT , if you only want to insert a row if the category_name text matches a row in the gamecategory table, you could use SQL like this:

INSERT INTO gamequestions (question_id, category_id)
SELECT NULL as question_id
     , c.category_id
  FROM gamecategory c
 WHERE c.category_name = ?
 ORDER BY c.category_id
 LIMIT 1

If there is no row in the gamecategory table with a category_name that matches the specified value (supplied where the ? is), then no row will be inserted.

If you want to go ahead and insert the row, even if the category_name text doesn't match, and have the category_id set to a default value of 0, then something like this, with a subquery in the SELECT list:

INSERT INTO gamequestions (question_id, category_id)
SELECT NULL as question_id
     , IFNULL(
         ( SELECT c.category_id
             FROM category c
            WHERE c.category_name = ?
            ORDER BY c.category_id
            LIMIT 1
         )
       ,0) AS category_id

The first step is really to get some SQL statements that do what you want.

The second step is to get the SQL text embedded into your application, with the appropriate bind variables/substitutions and avoiding SQL injection vulnerabilities. The second step is hard enough to figure out, without also having to work out the first step at the same time.

---

FOLLOWUP

If you are inserting a row into gamequestions , we'd expect the value for the question column to be supplied in the INSERT statement, it wouldn't be coming from a row in the gamequestions table.

The SELECT we're running as part of the INSERT is getting the value of category_id from the gamecategory table; there's no need for a JOIN to the gamequestions table.

I think you want SQL of the form:

 INSERT INTO gamequestions
 ( question_id
 , category_id
 , question
 , another_column
 , some_id
 )
 SELECT NULL
      , c.category_id       
      , 'my question text goes here'
      , 'fee fi fo fum'
      , 42
   FROM gamecategory c
  WHERE c.category_name = 'category name text goes here'
  ORDER BY c.category_id
  LIMIT 1

That will insert a new row, with the value of

• some_id set to integer value of 42
• another_column set to a string value of 'fee fi fo fum'
• question set to a string value of 'my question text goes here'
• category_id set to a value retrieved from the gamecategory table

Ideally, you wouldn't need to do a lookup of the category_id from the database at all; ideally, your combo box would display the category_name , but return a value of category_id , so you could just directly insert that:

 INSERT INTO gamequestions
 ( question_id
 , category_id
 , question
 , another_column
 , some_id
 ) VALUES
 ( NULL
 , 5
 , 'my question text goes here'
 , 'fee fi fo fum'
 , 42
 )

without having to run a SELECT on the insert.

Ideally, instead of returning the category_name text as a value, the combo box would return the appropriate category_id value. Put the "lookup" into the drop down

For example, represent the gamecategory table contents:

id  category_name
--  ---------------
 0  Uncategorized
 1  Action-Adventure
 2  Adventure
 3  Aerial Combat
 4  Fighting
 5  First Person Shooter
 6  Fitness

In an HTML combobox like this:

 <select name=category_id>
 <option value='0' selected>Uncategorized</option>
 <option value='1'>Action-Adventure      </option>
 <option value='2'>Adventure             </option>
 <option value='3'>Aerial Combat         </option>
 <option value='4'>Fighting              </option>
 <option value='5'>First Person Shooter  </option>
 <option value='6'>Fitness               </option>
 </select>

To get the value from the combobox in javascript, for example:

$('select[name="category_id"]').val();

FOLLOWUP

The question_id column could be omitted from the INSERT statement, then we wouldn't need to supply the NULL value for it.

 INSERT INTO gamequestions (category_id, question, another_column)
 VALUES (5, 'my question text goes here', 'fee fi fo fum');

-or-

 INSERT INTO gamequestions (category_id, question, another_column)
 SELECT 5, 'my question text goes here', 'fee fi fo fum'

FOLLOWUP

Q: what if I was to insert multiple rows into question column while using INSERT INTO gamequestions, so I can have ie 3 textfields each containing different question but each going to same game category INSERT INTO gamequestions ( question_id , category_id , question , another_column , some_id ) VALUES ( NULL , 5 , 'my question text goes here' , 'fee fi fo fum' , 42 )

A: Using the VALUES clause, you can do a multi-row insert (a very powerful and non-standard extension provided by MySQL).

The SQL that you would send to the database would need to look something like this:

INSERT INTO gamequestions (category_id,question,another_column,some_id)
VALUES 
 (5, 'my question text goes here'  , 'fee fi fo fum'     , 42)
,(5, 'another question to be added', 'i smell the blood' , 84)
,(5, 'and this is a third row'     , 'of an englishman'  , 17)

(I've omitted the question_id column, we'll let that be assigned the DEFAULT NULL value and the real value will be assigned by AUTO_INCREMENT. Note the column is still being "inserted" along with the rest of the row, we're just giving an incomplete list of columns, and letting MySQL assign default values for the columns we don't specify.)

The real "trick" here is that we have three rows, three sets of values. The set of values for each row is enclosed in parens, just like in the single row insert. But MySQL allows us to tack on a comma, and another set of values for another row.

The category_id assigned on each row has to be individually supplied for each row, it can be the same value as previous rows, or entirely different, doesn't make any difference. (The only difference the values make is whether MySQL is going to throw an error, because of a constraint violation, a problem with converting datatypes, something like that.)

(MySQL ignores all that spacing, I just added the spacing to make it more readable.)