MYSQL - SELECT data from dynamic table names - mysql

Question

Imagine that I have several dynamic table names such as :
select table_name
from INFORMATION_SCHEMA.TABLES
where table_name like 'ifhcraw%';
ifhcraw_2016_03_25_13
ifhcraw_2016_03_26_19
ifhcraw_2016_03_28_2
And I don't found any rule on names. To find last edited table I have just select last modified table with query :
select table_name
from INFORMATION_SCHEMA.TABLES
where table_name like 'ifhcraw%' and
update_time = (select max(update_time)
from INFORMATION_SCHEMA.TABLES
where table_name like 'ifhcraw%');
Now the purpose all of this step to get data from table_name.
I have tried to use variables , however it was failed. For example :
SET #query1 := 'select table_name
from INFORMATION_SCHEMA.TABLES
where table_name like \'ifhcraw%\' and
update_time = (select max(update_time)
from INFORMATION_SCHEMA.TABLES
where table_name like \'ifhcraw%\') ';
SET #query2 := concat('select *
from ', #query1);
PREPARE stmt from #query2;
execute stmt;
Please help to solve issue.

Answer 1

Try:
mysql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 5.7.11 |
+-----------+
1 row in set (0.00 sec)
mysql> DROP TABLE IF EXISTS `ifhcraw_2016_03_25_13`;
Query OK, 0 rows affected (0.00 sec)
mysql> DROP TABLE IF EXISTS `ifhcraw_2016_03_26_19`;
Query OK, 0 rows affected (0.00 sec)
mysql> DROP TABLE IF EXISTS `ifhcraw_2016_03_28_2`;
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `ifhcraw_2016_03_25_13` (
-> `id` INT
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `ifhcraw_2016_03_26_19` (
-> `id` INT
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `ifhcraw_2016_03_28_2` (
-> `id` INT
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> SET #`TABLE_NAME` := NULL;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT `TABLE_NAME` INTO #`TABLE_NAME`
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%' AND
-> `UPDATE_TIME` = (SELECT MAX(`UPDATE_TIME`)
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%'
-> );
Query OK, 0 rows affected, 1 warning (0.01 sec)
mysql> SELECT #`TABLE_NAME`;
+---------------+
| #`TABLE_NAME` |
+---------------+
| NULL |
+---------------+
1 row in set (0.00 sec)
mysql> SET #`qry` := IF(#`TABLE_NAME` IS NULL,
-> 'SELECT NULL',
-> CONCAT('SELECT * FROM ', #`TABLE_NAME`));
Query OK, 0 rows affected (0.00 sec)
mysql> PREPARE `stmt` FROM #`qry`;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> EXECUTE `stmt`;
+------+
| NULL |
+------+
| NULL |
+------+
1 row in set (0.00 sec)
mysql> DEALLOCATE PREPARE `stmt`;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO `ifhcraw_2016_03_26_19`
-> (`id`)
-> VALUES
-> (1);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT `TABLE_NAME` INTO #`TABLE_NAME`
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%' AND
-> `UPDATE_TIME` = (SELECT MAX(`UPDATE_TIME`)
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%'
-> );
Query OK, 1 row affected (0.00 sec)
mysql> SELECT #`TABLE_NAME`;
+-----------------------+
| #`TABLE_NAME` |
+-----------------------+
| ifhcraw_2016_03_26_19 |
+-----------------------+
1 row in set (0.00 sec)
mysql> SET #`qry` := IF(#`TABLE_NAME` IS NULL,
-> 'SELECT NULL',
-> CONCAT('SELECT * FROM ', #`TABLE_NAME`));
Query OK, 0 rows affected (0.00 sec)
mysql> PREPARE `stmt` FROM #`qry`;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> EXECUTE `stmt`;
+------+
| id |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
mysql> DEALLOCATE PREPARE `stmt`;
Query OK, 0 rows affected (0.00 sec)
UPDATE
Care should be taken when there are two or more tables that match the criteria, will fail as follows:
mysql> INSERT INTO `ifhcraw_2016_03_26_19`
-> (`id`)
-> VALUES
-> (1);
Query OK, 1 row affected (0,00 sec)
mysql> INSERT INTO `ifhcraw_2016_03_28_2`
-> (`id`)
-> VALUES
-> (1);
Query OK, 1 row affected (0,00 sec)
mysql> SELECT `TABLE_NAME`
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%' AND
-> `UPDATE_TIME` = (SELECT MAX(`UPDATE_TIME`)
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%'
-> );
+-----------------------+
| TABLE_NAME |
+-----------------------+
| ifhcraw_2016_03_26_19 |
| ifhcraw_2016_03_28_2 |
+-----------------------+
2 rows in set (0,00 sec)
mysql> SELECT `TABLE_NAME` INTO #`TABLE_NAME`
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%' AND
-> `UPDATE_TIME` = (SELECT MAX(`UPDATE_TIME`)
-> FROM `INFORMATION_SCHEMA`.`TABLES`
-> WHERE `TABLE_NAME` LIKE 'ifhcraw%'
-> );
ERROR 1172 (42000): Result consisted of more than one row
You should handle the case as you deem appropriate.