How to use variable as the table identifier in MYSQL - mysql

If i have this:
CREATE TABLE ftable (
id INT,
fvalue VARCHAR(14)
);
INSERT INTO ftable VALUES (1,'tableB'),(2,'tableA');
CREATE TABLE tableA (
value VARCHAR(14)
);
SELECT #tmp:=fvalue FROM ftable WHERE id=2;
How do I make it so I can do this:
INSERT INTO #tmp VALUES ('buhambug');
Becuase as far I know that throws a mysql error.Can someone show me a sqlfiddle of the solution? Or maybe I'm thinking about this the wrong way?


You need to use dynamic SQL to use a variable as an object name:
SET #tmp = (SELECT fvalue FROM ftable WHERE id=2);
SET #SQL = CONCAT('INSERT INTO ',#tmp,' VALUES (''buhambug'')');
PREPARE stmt FROM #SQL;
EXECUTE stmt;
SQL FIDDLE


You can't do in static sql.
You can do it in stored procedure:
delimiter $$
drop procedure if exists test_call$$
create procedure test_call(table_in varchar(100))
begin
set #q = concat("select * from ", table_in);
PREPARE stmt FROM #q;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
end$$
delimiter ;
call test_call('TeableA');
drop procedure if exists test_call;
In general dynamic read from dynamic tables is not a good decision

Related

Logic condition to avoid duplicate entries in stored procedure

I have the following stored procedure . I'm trying to insert the users from the table usuaris, whose admin variable is equal to 1, into the table that the stored procedure creates with the name( nombre varchar(50)) that is passed as a parameter.
When the procedure is called, it duplicates the user 'mary' with id 4. I've tried a couple of ways to implement the logic condition in order to avoid the duplication, but still, I'm missing something and I can't get the desired result. In the code below, the logic condition before the insertion is the last thing I've tried. Any ideas?
Thanks.
CREATE DEFINER=`root`#`localhost` PROCEDURE `createNewtable`(nombre varchar(50))
BEGIN
/*variable declaration*/
declare centinela int ;
declare id1 int ;
declare nom1 varchar(50);
declare admin1 enum('0','1') ;
declare cadena varchar(100); /*string to concatenate table creation and insertion*/
/*cursor declaration*/
declare cursor1 cursor for select * from users.usuaris where admin = '1' ;
declare continue handler for not found set #centinela = 1 ;
/*create the table with the name that's passed as parameter*/
set #cadena=concat("create table ",nombre,
"(
id2 int not null primary key,
nom2 varchar(50),
admin2 enum ('0','1')
)" );
prepare stmt from #cadena ;
execute stmt ;
deallocate prepare stmt;
/* loop that fetches the data from the table usuaris and
inserts them into the newly created table. */
set #centinela = 0 ;
open cursor1 ;
bucle: loop
fetch cursor1 into id1,nom1,admin1 ;
if ( centinela = 1 ) then
leave bucle ;
end if ;
/*logic condition to avoid entry duplication */
if not exists (select * from users.usuaris where admin='1' and id=#id1) then
set #cadena=concat("insert into ",nombre," values( ",id1,",'",nom1,"','",admin1,"')");
end if;
select #cadena;
prepare stmt from #cadena;
execute stmt ;
deallocate prepare stmt;
end loop bucle;
close cursor1;
END
Here is the single-table database of users :
create database if not exists `users` ;
use `users` ;
create table usuaris(
id int not null auto_increment primary key ,
nom varchar(50),
admin enum ('0','1')
);
insert into usuaris(id,nom,admin)
values
(1,'jose','1'),
(2,'maria','0'),
(3,'frank','1'),
(4,'mary','1'),
(5,'godfrey','0') ;

Also it has to duplicate jose. The reason of duplication - if the IF statement isn't TRUE then you don't set the new #cadena variable BUT anyway execute PREVIOUS #cadena statement. You should move execution into the IF statement also:
if not exists (select * from users.usuaris where admin='1' and id=#id1) then
set #cadena=concat("insert into ",nombre," values( ",id1,",'",nom1,"','",admin1,"')");
select #cadena;
prepare stmt from #cadena;
execute stmt ;
deallocate prepare stmt;
end if;
Also in SQL you should always try to avoid loops if it possible and use SQL statements instead.
You can replace your loop with one SQL statement:
INSERET INTO NEW_TABLE_NAME_HERE
SELECT id1,nom1,admin1
FROM users.usuaris where admin<>'1'
Further more you can use SELECT INTO statement syntax to automatically create new table without CREATE TABLE statement:
SELECT id1 as id2,
nom1 as nom2,
admin1 as admin2
INTO NEW_TABLE_NAME_HERE
FROM users.usuaris where admin<>'1'

Change ur below code to my new code and try-
Existing Code
if not exists (select * from users.usuaris where admin='1' and id=#id1) then
set #cadena=concat("insert into ",nombre," values( ",id1,",'",nom1,"','",admin1,"')");
end if;
select #cadena;
prepare stmt from #cadena;
execute stmt ;
deallocate prepare stmt;
New Code-
SET #cnt=SELECT count(*) FROM users.usuaris WHERE admin='1' AND id=#id1
IF #cnt>0 THEN
SET #cadena=CONCAT("insert into ",nombre," values( ",id1,",'",nom1,"','",admin1,"')");
prepare stmt from #cadena;
execute stmt ;
deallocate prepare stmt;
end if;

How can i create a procedure for select statement in 'IN Clause' for phpmyadmin

I want to create a procedure for a select query in which the where clause will have a IN Clause. I had created one procedure like below butu its not working-
CREATE DEFINER = `root`#`localhost` PROCEDURE `agentin` ( IN `code` VARCHAR( 100 ) ) NOT DETERMINISTIC NO SQL SQL SECURITY DEFINER
BEGIN
SELECT * FROM AgentInformation WHERE AgentCode IN (code);
END
After putting the In clause values like --> IN ('CG001','CG002')
I am getting null values and the query made by phpmyadmin was
SET #p0 = '''CG001'',''CG002''';
CALL agentin (
#p0
);
Please help regarding it , Thanks

Here it is an example -
DELIMITER $$
CREATE PROCEDURE procedure1(IN id_param VARCHAR(255))
BEGIN
SET #sql = CONCAT('SELECT * FROM table WHERE id IN (', id_param, ')');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;
SET #id = '1,2,3,4,5';
CALL procedure1(#id);

MySQL stored procedure Error - Create table from param names

I'm trying the following but I'm getting the following error:
ERROR 1054 (42S22): Unknown column 'f' in 'where clause'
I'm seriously confused because f is a parameter of createtableTest...
CREATE PROCEDURE createtableTest
(
tname2 varchar(20),
f varchar(20)
)
BEGIN
DROP TABLE IF EXISTS tname2;
CREATE TABLE tname2 as SELECT * FROM data WHERE group_name like f;
END;

Since f is contains the value, a dynamic sql is needed so we can concatenate it with the original query,
DELIMITER $$
CREATE PROCEDURE createtableTest(IN tname2 varchar(20),IN f varchar(20))
BEGIN
DROP TABLE IF EXISTS tname2;
SET #sql = CONCAT('CREATE TABLE tname2 as SELECT * FROM data WHERE group_name like ''%',f,'%''');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END $$
DELIMITER ;
for example, the value of f is hello, the concatenated string will produce
CREATE TABLE tname2 as SELECT * FROM data WHERE group_name like '%hello%'
UPDATE
MySQL Prepared Statements
Aside from concatenation, you can also parameterized the value which is the best way, ex
DELIMITER $$
CREATE PROCEDURE createtableTest(IN tname2 varchar(20),IN f varchar(20))
BEGIN
DROP TABLE IF EXISTS tname2;
SET #sql = CONCAT('CREATE TABLE tname2 as SELECT * FROM data WHERE group_name like ?');
PREPARE stmt FROM #sql;
SET #val = CONCAT('%', f, '%');
EXECUTE stmt USING #val;
DEALLOCATE PREPARE stmt;
END $$
DELIMITER ;

Using Prepared statement in Dynamic view

Here is my code
Drop procedure if exists test//
CREATE PROCEDURE test(IN woeid VARCHAR(15))
BEGIN
SET #w1 := woeid;
SET #sql = CONCAT('CREATE OR REPLACE VIEW temp
AS
SELECT *
FROM test_table gp
WHERE gp.name =', #w1);
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END//
Delimiter ;
call test('ABCD');
I am getting error as
Error code: 1054. Unknown column 'ABCD' in 'where' clause
Please help.

It sounds as though you're needlessly using views, when some other approach would be more appropriate.
However, the reason it isn't working is that you haven't quoted your string literal, so the resulting SQL contains WHERE gp.name = ABCD whereas it at very least needs to be WHERE gp.name = 'ABCD'. You can use MySQL's QUOTE() function for this purpose, but it's better to parameterise the value:
DELIMITER //
DROP PROCEDURE IF EXISTS test//
CREATE PROCEDURE test(IN woeid VARCHAR(15))
BEGIN
SET #w1:=woeid, #sql:=CONCAT('
CREATE OR REPLACE VIEW temp AS
SELECT *
FROM test_table
WHERE name = ?
');
PREPARE stmt FROM #sql;
EXECUTE stmt USING #w1;
DEALLOCATE PREPARE stmt;
SET #w1:=NULL, #sql:=NULL;
END//
DELIMITER ;
CALL test('ABCD');

How to send table name as Mysql Store procedure

I write a store procedure.But it don't take the table name as a parameter.Now how i send a table name as aparameter.Pls see my proc below:
DELIMITER $$
USE `db_test`$$
DROP PROCEDURE IF EXISTS `test_proc`$$
CREATE DEFINER=`root`#`localhost` PROCEDURE `test_proc`(IN newsInfoTable VARCHAR(100))
BEGIN
SELECT news INTO #news
FROM newsInfoTable
WHERE CURDATE()=DATE_FORMAT(date_time,'%Y-%m-%d')
ORDER BY date_time DESC LIMIT 1;
SELECT #news;
END$$
DELIMITER ;
Calling parameter:
USE db_test;
CALL test_proc('tbl_news_list');
But the ERROR is: Table 'db_test.newsinfotable' doesn't exist
How solve this problem.Pls help.

Use prepared statements in your procedure body:
SET #s = CONCAT('SELECT ... FROM ', newsInfoTable);
PREPARE stmt FROM #s;
EXECUTE stmt;
//.....
DEALLOCATE PREPARE stmt;
Your code should look like :
SET #sql_stam = CONCAT('SELECT news INTO #news FROM ',newsInfoTable,
' WHERE DATE_FORMAT(date_time,\'%Y-%m-%d\')
ORDER BY date_time DESC LIMIT 1');
...
SELECT #news;
Also, I don't see any reasons you need to use #news variable...