How can i add dynamic column in table exists with mysql? - mysql

i have table and i want to add column but the name of column will be variable
like this :
$coulName = col_1_2;
ALTER TABLE `table name` ADD `$coulmName` DOUBLE NOT NULL DEFAULT '0' AFTER `col2`;
how can i do that ?


You need to use a prepared statement for this:
SET #colName = 'col_1_2';
SET #s = CONCAT('ALTER TABLE `mytable` ADD `', #colName,
'` DOUBLE NOT NULL DEFAULT 0 AFTER `col2`');
PREPARE stmt1 FROM #s;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;


Within MySQL you can only achieve this using prepared statements because you cannot tie a variable to a table or column name. This means that you have to assemble the sql statement in a string and execute it.
However, you can accomplish this from your application code as well - the variable name suggests that you may use php. The same applies: you have to concatenate the sql statement string, cannot use parameters.
Code would look sg like the below in MySQL:
#coulName = 'col_1_2';
#sql = 'ALTER TABLE `table name` ADD `',#coulmName,'` DOUBLE NOT NULL DEFAULT '0' AFTER `col2`;
PREPARE stmt1 FROM #sql;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;
However, I'm not sure if it a really good idea to regularly and dynamically change the existing data structure. That usually indicates poor database design.

Related

Table in FROM clause defined by variable in MySQL

I want to create a SQL script for MySQL 5.7 that inserts data from a table of a database origin into a table of another target database.
I want to have this source-database defined by a variable.
USE my_target_db;
SET #origin_db='my_origin_db';
SET #origin_table = concat(#origin_db,'.','tablename');
INSERT INTO target_table SELECT * FROM #origin_table;
Variables are used in various example to define column names but I never seen a way to define a table with it.
Is anyone has a trick for this ?

Variables won't use in table name in MySQL. You only can use a prepared statement for dynamic build query. For example:
USE my_target_db;
SET #origin_db='my_origin_db';
SET #origin_table = CONCAT(#origin_db,'.','tablename');
SET #query = CONCAT('INSERT INTO target_table SELECT * FROM ', #origin_table);
PREPARE stmt FROM #query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
You can read more detail about it in official documentation

You can use Prepared Statement like this:
USE my_target_db;
SET #origin_db='my_origin_db';
SET #origin_table = concat(#origin_db,'.','tablename');
SET #qry1 = concat('INSERT INTO target_table SELECT * FROM ', #origin_table);
PREPARE stmt1 from #qry1;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;

How to convert an SQL select query into a formatted HTML table within a MySQL function

I'm looking for a way to generate valid HTML code within MySQL (without PHP) by converting any query output into an HTML table.
Here's my progress so far and evidently, I'm stuck. I hope I can get some help, thanks.
1. "dynSQL" - A procedure to take any Select query and create a named table out of it
Since MySQL doesn't allow dynamic queries in functions, I'm calling a procedure that creates a named table, tmp. I can't use a temporary table because info about temporary tables is not available in information_schema (in mysql 5.6)
CREATE DEFINER=`root`#`%` PROCEDURE `dynSQL`(SQL_QUERY TEXT)
BEGIN
set #SQLQ := 'Drop table if exists tmp;';
PREPARE stmt from #SQLQ;
Execute stmt;
SET #SQLQ := concat('create table tmp as ',SQL_QUERY);
PREPARE stmt from #SQLQ;
Execute stmt;
-- I'm adding a auto increment ID column to be able to loop through the rows later
SET #SQLQ := "ALTER TABLE tmp add column CustColHTML_ID INT NOT NULL AUTO_INCREMENT FIRST, ADD primary KEY Id(CustColHTML_ID)";
PREPARE stmt from #SQLQ;
Execute stmt;
DEALLOCATE PREPARE stmt;
END
2. "MakeHTML" - Function to read from the table tmp and return a formatted HTML table
CREATE DEFINER=`root`#`%` FUNCTION `MakeHTML`() RETURNS text CHARSET utf8
DETERMINISTIC
BEGIN
DECLARE HTML text default "<TABLE><TR>";
DECLARE rowCount int default 0;
DECLARE i int default 0;
select concat('<TR>',group_concat('<TD>',column_name,'</TD>' separator ''),'</TR>') into html from information_Schema.`columns` where table_name='tmp';
Select max(CustColHTML_ID) into rowCount from `tmp`; -- Set the row counter
WHILE i<=rowCount DO
-- What do I do here? How do I loop through the columns of table tmp?
set i:=i+1;
END WHILE;
RETURN HTML;
END
As you can see, I'm stuck at looping through the unknown and dynamic columns of table tmp. I read about how a cursor can be used here, but all the examples I saw make use of known columns and assign those into named variables. However, since the query itself is dynamic, I wouldn't know the names of the columns.
I'd really appreciate your time and assistance, thanks!
p.s. I've posted this as a new question because my earlier question was marked as closed as being too broad. I subsequently edited my question but it was still showing as Closed. I've therefore deleted the older question and replaced it with this one.

With a sample table as such:
CREATE TABLE tmp (ID INT, Col1 INT, Col2 INT);
The SQL you would need to generate your HTML is:
SELECT CONCAT('<table>', GROUP_CONCAT(CONCAT('<tr><td>',ID,'</td><td>',Col1,'</td><td>',Col2,'</td><tr>')), '</table>')
FROM tmp;
You can generate this using the INFORMATION_SCHEMA:
SELECT CONCAT
(
'SELECT CONCAT(''<table>'', GROUP_CONCAT(CONCAT(''<tr>'', ',
GROUP_CONCAT(CONCAT('''<td>'',', COLUMN_NAME, ',''</td>''')),
', ''</tr>'')), ''</table>'') FROM tmp'
)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tmp';
It is then just a case of executing this:
SET #SQL = (
SELECT CONCAT
(
'SELECT CONCAT(''<table>'', GROUP_CONCAT(CONCAT(''<tr>'', ',
GROUP_CONCAT(CONCAT('''<td>'',', COLUMN_NAME, ',''</td>''')),
', ''</tr>'')), ''</table>'') FROM tmp'
)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tmp'
);
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Example on SQL Fiddle
ADDENDEUM
Forgot to include table headers:
SET #SQL = (
SELECT CONCAT
(
'SELECT CONCAT(''<table><tr>'',',
GROUP_CONCAT(CONCAT('''<th>'',''', COLUMN_NAME, ''',''</th>''')),
', ''</tr>'', GROUP_CONCAT(CONCAT(''<tr>'', ',
GROUP_CONCAT(CONCAT('''<td>'',', COLUMN_NAME, ',''</td>''')),
', ''</tr>'')), ''</table>'') FROM tmp'
)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tmp'
);
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Example on SQL Fiddle

MySQL query, create table with variable

How do you include a variable into a create table query(.sql file)? I have tried everything to my knowledge, but it simply sets the #variable name itself as the table name instead of the actual variable.
(I.e it sets #preset as the name instead of "cart_")
SET #Preset='cart_';
CREATE TABLE IF NOT EXISTS `#preset,Customer` (....

You need dynamic sql. To do this, you are going to have to use prepared statements
Try something like:
SET #SQL = CONCAT('CREATE TABLE ',CONCAT('cart_',customer), ..;
PREPARE stmt FROM #SQL;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

How to get variable value as table name in select statement

SET Project_List_val=CONCAT(Project_Number_val,'_List');
Insert Into test (Manthan_Panel_Id) select Manthan_Panel_Id from Project_List_val where Project_Number_val='9';
In the insert statement there is the variable named 'Project_List_val' which consist of table name as concated in the above step. This statement is not taking the content of the variable as table name instead it is taking 'Project_List_val' as table name and giving table not found error.
Any suggestions?

By default you cannot parameterized table names and column names so you need to create Dynamic SQL for that,
SET #Project_List_val = CONCAT(Project_Number_val, '_List');
SET #projNum = 9;
SET #sql = CONCAT(' INSERT INTO test (Manthan_Panel_Id)
SELECT Manthan_Panel_Id
FROM ', #Project_List_val, '
WHERE Project_Number_val = ?');
PREPARE stmt FROM #sql;
EXECUTE stmt USING #projNum;
DEALLOCATE PREPARE stmt;

MySQL User-Defined Variable Values Can't be Used as Identifiers. How do I do this?

According to the manual:
User variables... cannot be used
directly in an SQL statement as an
identifier or as part of an
identifier, such as in contexts where
a table or database name is expected
Which explains why what I've been trying doesn't work:
set #databaseName := 'job_hunt_2';
drop database #databaseName;
create database #databaseName;
use #databaseName;
Is there a way to accomplish this, or is it simply impossible? Thanks!

may be you should try following approach:
set #databaseName := 'job_hunt_2';
SET #s = CONCAT('drop database ', #databaseName);
PREPARE stmt1 FROM #s;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;