Question

I’m working on an old database already in use for years and really crappy designed.
There is a table, “Articles”, which contains a “code” column that will be our PK.
And many tables like “idXXXXX” where XXXXX is a “code” value with exactly the same structure.
I looked at the application using this database and saw that relations between tables is made there.

I’m not affraid of redesign the database access in the application, but I don’t want to lose years of entries in the database.

I want to create a “campain” table which will have an “id” PK and a “id_code” as FK linking “campain” to “articles”

I’m not a SQL master but I know I can get tables names with

SELECT TABLE_NAME FROM INFORMATION_SCHEMA WHERE TABLE_NAME LIKE 'id%'

But I have really no idea about how to deal with the result (which is fine).
So how can I access to every tables named “idXXX” and insert every rows in the “campain” table + set “id_code” column to “XXX”?

---

Here is the procedure I saved (I didn’t add every fields in the INSERT line for testing purpose) :

CREATE PROCEDURE JoinAllTables()
BEGIN

 DECLARE done INT default 0;
 DECLARE tableName CHAR(9); 
 DECLARE buffStr CHAR(7);
 DECLARE buffId INT default 0;

 DECLARE cur1 CURSOR FOR SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME LIKE 'id%'; 
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;


 OPEN cur1;

 read_loop: LOOP
    FETCH cur1 INTO tableName;
    IF done THEN
       LEAVE read_loop;
    END IF;

  SET buffStr = SUBSTRING(tableName, 3);
  SET buffId = CAST(buffStr AS SIGNED);

  set @sql = CONCAT("INSERT INTO campagnes(id, id_code) SELECT null, bufId FROM ",tableName); # Dynamically building sql statement 
  PREPARE stmt FROM @sql;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt; 

  END LOOP;
  CLOSE cur1;
END;

As u can see, I sub ‘idXXXXX’ to ‘XXXXX’ then CAST it AS INTEGER (SIGNED).
But I guess that in the “INSERT INTO” line, second tableName doesn’t point to the variable. That’s why I’m getting a
“#1446 – Tabble ‘bddsoufflage.tablename’doesn’t exist” Error 🙂 Any idea ?

Answer 1

Edit: Updated answer

We can’t have the tableName dynamically changed inside a prepared statement, so we must go through DynamicSQL to build the query using CONCAT, then compile the SQL with PREPARE, EXECUTE it and DEALLOCATE it.

DELIMITER //
CREATE PROCEDURE JoinAllTables()
BEGIN

 DECLARE done INT default 0;
 DECLARE tableName CHAR(9); 
 DECLARE buffStr CHAR(7);
 DECLARE buffId INT default 0;

 DECLARE cur1 CURSOR FOR SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME LIKE 'id%'; 
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

 OPEN cur1;

 read_loop: LOOP
    FETCH cur1 INTO tableName;
    IF done THEN
       LEAVE read_loop;
    END IF;

  SET buffStr = SUBSTRING(tableName, 3);
  SET buffId = CAST(buffStr AS SIGNED);

  set @sql = CONCAT("INSERT INTO campagnes(id, id_code) SELECT null, ", buffId, " FROM ",tableName); # Dynamically building sql statement 
  PREPARE stmt FROM @sql;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt; 

  END LOOP;
  CLOSE cur1;
END; //

See also this answer MySQL Pass table name to cursor select

Old answer
The procedure should look something like this. Thanks Mchl for providing an Insert Into query example, I simply added it to the rest of the procedure.

DELIMITER //
CREATE PROCEDURE JoinAllTables()
BEGIN

 DECLARE done INT default 0;
 DECLARE tableName CHAR(7); # Variable to contain table names CHAr(7) is assuming id + 5Xs as characters.

 DECLARE cur1 CURSOR FOR SELECT TABLE_NAME FROM INFORMATION_SCHEMA WHERE TABLE_NAME LIKE 'id%'; # Create a cursor to iterate over the tables
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

 OPEN cur1;

 read_loop: LOOP
    FETCH cur1 INTO tableName;
    IF done THEN
      LEAVE read_loop;
    END IF;

    #Your Insert statement here, using tableName as a field.
INSERT INTO campain (id, id_code, otherfields) SELECT null, tableName, otherfields FROM tableName;

  END LOOP;
  CLOSE cur1;
END;//