Question

I am running through a dataset with a cursor.
In each cursor pass a string gets split up using a stored procedure which writes the single elements in a temporary table SplitValues, one value per row. Each dataset also has a unique ID ds_id

SplitValues

value   |
--------+
Item1   | 
Item2   | 
Item3   | `

I also have a reference table which has IDs for each of the items the split function could possibly produce:

classes

id | class |
---+--------
5  | Item1 |
6  | Item2 |
7  | Item3 |
8  | Item4 |
9  | Item5 |

What I now want to do is to go through all rows of SplitValues and write them to a table to store the data, however using the ID of the class and not the class itself to save storage:

storage

ds_id | class_id |
------+-----------
0     | 5        |
0     | 6        |
0     | 7        |

This should be fairly simple but I am failing. I did multiple attempts, one was the following cursor loop:

FETCH cur1 INTO ds_id, string;
CALL `Split_String`(string, ',');

INSERT INTO storage (ds_id, class_id) 
    SELECT ds_id, 
        (SELECT classes.id FROM classes WHERE class = SplitValues.value ) as class_id ;

[...]

Error produced Unknown column 'SplitValues.value' in 'where clause'

I have searched a lot and think my problem is somehow related to aliases but was unable to find a solution.

Answer 1

Try this

[...]
INSERT INTO storage (ds_id, class_id) 
SELECT ds_id, c.id
  FROM classes c INNER JOIN 
       SplitValues s ON c.class = s.value
[...]

Here is sqlfiddle