So, I import a CSV file into MySQL Workbench and the datetime columns are changed to text. I can't perform any calculations.
How do I convert the entire column from text to datetime? For example the date is in this format 2022-01-13 11:59:47, how do I change this to datetime?
Here's a demo:
mysql> create table mytable ( t text );
Query OK, 0 rows affected (0.02 sec)
mysql> insert into mytable set t = '2022-01-13 11:59:47';
Query OK, 1 row affected (0.00 sec)
mysql> select * from mytable;
+---------------------+
| t |
+---------------------+
| 2022-01-13 11:59:47 |
+---------------------+
1 row in set (0.00 sec)
mysql> alter table mytable modify column t datetime;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> show create table mytable\G
*************************** 1. row ***************************
Table: mytable
Create Table: CREATE TABLE `mytable` (
`t` datetime DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3
1 row in set (0.00 sec)
mysql> select * from mytable;
+---------------------+
| t |
+---------------------+
| 2022-01-13 11:59:47 |
+---------------------+
1 row in set (0.01 sec)
If you have any rows in your text column that aren't valid datetime values, they won't be converted successfully. In those cases, they'll turn into NULL. So be careful and create a backup before you do this alter table.
Better yet, do this operation on a copy of your data in another table, until you are confident it will work as you expect. Never try a potentially destructive change on the only copy of your data.
Run the query on your data:
select cast(textdate as datetime)
from t;
show warnings;
If there are no warnings in the attempted datetime conversion, proceed with alter table:
alter table mytable modify column textdate datetime;
Related
Table with
field abd text
field hash_code varchar
I would like to have in hash_code the md5 value of abd field without to do so from the code.
is that possibile?
Thanks
mysql> create table mytable ( abd varchar(100), hash_code char(32) as (md5(abd)) );
Query OK, 0 rows affected (0.01 sec)
mysql> insert into mytable set abd = 'now is the time for all good men to come to the aid of their country';
Query OK, 1 row affected (0.01 sec)
mysql> select * from mytable\G
*************************** 1. row ***************************
abd: now is the time for all good men to come to the aid of their country
hash_code: 60a5d53255faa66033c9851adb40947a
This seems to be a bug in MySql. Posting it here to confirm my conclusion and share my experience. We are currently migrating from MS SQL Server to MySql Community Edition 5.7.12. There is a Dealers table which has a virtual computed column. It was being referred in the join of a query used inside a trigger. As a result of this, the MySql Server got re-started.
To make sure that there was no other cause to the event, we had created a dummy table without computed columns and referred to that table in the trigger. The trigger executed successfully. Then, we had created another dummy table with the computed column. We had just referred the table in the join without the reference to the computed column. When the trigger was fired, the server crashed inspite of the fact that only a actual column of the table was referred and there was no reference to the computed column. Thus, you cannot even refer a table with computed columns in the triggers.
What we have done temporarily is to convert the virtual columns into actual columns and modified the queries of select, insert and update on the table.
Is there a better alternative to solve this issue?
Can you post your test example?. I can't reproduce the problem on my test example.
mysql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 5.7.12 |
+-----------+
1 row in set (0.00 sec)
mysql> DROP TABLE IF EXISTS `t2`;
Query OK, 0 rows affected (0.00 sec)
mysql> DROP TABLE IF EXISTS `t1`;
Query OK, 0 rows affected (0.00 sec)
-- Table with Generated Column
mysql> CREATE TABLE IF NOT EXISTS `t1` (
-> `c0` INTEGER UNSIGNED NOT NULL PRIMARY KEY,
-> `value` VARCHAR(20),
-> `c1` INTEGER UNSIGNED GENERATED ALWAYS AS (`c0`) VIRTUAL
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE IF NOT EXISTS `t2` (
-> `c1` INTEGER UNSIGNED NOT NULL PRIMARY KEY,
-> `value` VARCHAR(20)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO `t2` (`c1`, `value`) VALUES (1, 'value 1');
Query OK, 1 row affected (0.00 sec)
mysql> DELIMITER ||
mysql> DROP TRIGGER IF EXISTS `t1_ins_bef`||
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> CREATE TRIGGER `t1_ins_bef` BEFORE INSERT ON `t1`
-> FOR EACH ROW
-> BEGIN
-> SET NEW.`value` := (SELECT `t2`.`value`
-> FROM `t1`
-> INNER JOIN `t2` ON `t1`.`c1` = `t2`.`c1`);
-> END||
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> INSERT INTO `t1` (`c0`) VALUES (1), (2);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT
-> `c0`,
-> `value`,
-> `c1`
-> FROM
-> `t1`;
+----+---------+------+
| c0 | value | c1 |
+----+---------+------+
| 1 | NULL | 1 |
| 2 | value 1 | 2 |
+----+---------+------+
2 rows in set (0.00 sec)
mysql> SELECT
-> `c1`,
-> `value`
-> FROM
-> `t2`;
+----+---------+
| c1 | value |
+----+---------+
| 1 | value 1 |
+----+---------+
1 row in set (0.00 sec)
I created two tables
CREATE TABLE `prova` (
`id` int NOT NULL AUTO_INCREMENT ,
`text` varchar(255) NOT NULL ,
PRIMARY KEY (`id`)
)
;
CREATE TABLE `prova2` (
`id2` int NOT NULL AUTO_INCREMENT ,
`text2` varchar(255) NOT NULL ,
PRIMARY KEY (`id2`)
)
;
insert into prova (text) values ('ffffff');
A function does a select on table one and inserts a row in table two only if the value of variable #test is set to 0:
CREATE FUNCTION `get_prova`()
RETURNS int(11)
BEGIN
declare id_prova int ;
declare test int ;
set #test = 1;
set #id_prova = (select id from prova limit 1);
if (#test = 0) THEN
insert into prova2 (text2) values ('dddd');
end if;
return #id_prova;
END;
then, I create a view that calls this function:
create view temp_prova as
select id,
text,
get_prova() as prova
from prova
I want to create table 3 that contains the result of view:
CREATE TABLE zzz_prova SELECT * FROM temp_prova;
but when I try to create table zzz_prova I get this error:
[SQL]CREATE TABLE zzz_prova SELECT * FROM temp_prova; [Err] 1746 -
Can't update table 'prova2' while 'zzz_prova' is being created.
Why does this error show up?
Thank you
What version of MySQL are you running?
Changes in MySQL 5.6.2 (2011-04-11)
Incompatible Change; Replication: It is no longer possible to issue a
CREATE TABLE ... SELECT statement which changes any tables other than
the table being created. Any such statement is not executed and
instead fails with an error.
One consequence of this change is that FOR UPDATE may no longer be
used at all with the SELECT portion of a CREATE TABLE ... SELECT.
This means that, prior to upgrading from a previous release, you
should rewrite any CREATE TABLE ... SELECT statements that cause
changes in other tables so that the statements no longer do so.
This change also has implications for statement-based replication
between a MySQL 5.6 (or later slave) and a master running a previous
version of MySQL. In such a case, if a CREATE TABLE ... SELECT
statement on the master that causes changes in other tables succeeds
on the master, the statement nonetheless fails on the slave, causing
replication to stop. To keep this from happening, you should either
use row-based replication, or rewrite the offending statement before
running it on the master. (Bug #11749792, Bug #11745361, Bug #39804,
Bug #55876)
References: See also Bug #47899.
UPDATE
MySQL 5.5:
mysql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 5.5.47 |
+-----------+
1 row in set (0.00 sec)
mysql> DROP FUNCTION IF EXISTS `f`;
Query OK, 0 rows affected (0.00 sec)
mysql> DROP TABLE IF EXISTS `t1`;
Query OK, 0 rows affected (0.00 sec)
mysql> DROP TABLE IF EXISTS `t2`;
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER |
mysql> CREATE FUNCTION `f`()
-> RETURNS INT
-> BEGIN
-> INSERT INTO `t2` VALUES (1);
-> RETURN 1;
-> END|
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> CREATE TABLE `t2`(`c1` INT);
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `t1` SELECT `f`() `c1`;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> SELECT `c1` FROM `t1`;
+------+
| c1 |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
mysql> SELECT `c1` FROM `t2`;
+------+
| c1 |
+------+
| 1 |
+------+
1 row in set (0.00 sec)
MySQL 5.6:
mysql> SELECT VERSION();
+-----------------+
| VERSION() |
+-----------------+
| 5.6.25 |
+-----------------+
1 row in set (0.00 sec)
mysql> DROP FUNCTION IF EXISTS `f`;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> DROP TABLE IF EXISTS `t1`;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> DROP TABLE IF EXISTS `t2`;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> DELIMITER |
mysql> CREATE FUNCTION `f`()
-> RETURNS INT
-> BEGIN
-> INSERT INTO `t2` VALUES (1);
-> RETURN 1;
-> END|
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;
mysql> CREATE TABLE `t2`(`c1` INT);
Query OK, 0 rows affected (0.00 sec)
mysql> CREATE TABLE `t1` SELECT `f`() `c1`;
ERROR 1746 (HY000): Can't update table 't2' while 't1' is being created.
This question already has answers here:
Concatenating a string and primary key Id while inserting
(2 answers)
Closed 6 years ago.
I have a table with 2 columns. The ID column auto increments. I'm trying to auto increment the user column with the same ID as the id column, but with a "user" prefix (example: user100, where the ID is also 100) basically just like what is done on stackoverflow.
CREATE TABLE test_table (
id MEDIUMINT NOT NULL AUTO_INCREMENT,
user CHAR(30) NOT NULL,
PRIMARY KEY (id)
) ENGINE=MyISAM;
Is there a way of doing this in 1 query? Instead of inserting into the DB, then querying to get the ID, and inserting the ID into the user column?
Use a BEFORE trigger:
DELIMITER $$
CREATE TRIGGER test_table_trigger
BEFORE INSERT ON test_table
FOR EACH ROW BEGIN
SET NEW.`user` = CONCAT(NEW.`user`, NEW.id);
END $$
DELIMITER ;
Documentation: MySQL triggers
You can do a trigger
Before Trigger:
mysql> truncate table test_table;
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter $$
mysql> CREATE TRIGGER test_table_trigger
-> BEFORE insert ON test_table
-> FOR EACH ROW
-> BEGIN
-> SET new.user = CONCAT('user', (SELECT AUTO_INCREMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA=DATABASE() AND TABLE_NAME='test_table'));
-> END $$
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql> INSERT INTO test_table values ();
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> INSERT INTO test_table values ();
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> INSERT INTO test_table values ();
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> select * FROM test_table;
+----+-------+
| id | user |
+----+-------+
| 1 | user1 |
| 2 | user2 |
| 3 | user3 |
+----+-------+
3 rows in set (0.00 sec)
The above should then use the auto-increment after it's designated to the id column and append it to the string user. The auto increment ID is pulled from Information_Schema, as if this is in a transaction or many queries, it could be set wrong.
Maybe you can try this, picking up last inserted id and concatenating string with converted value:
INSERT INTO test_table (user) VALUES ('user')
UPDATE test_table
SET user = user + CAST(LAST_INSERT_ID() AS VARCHAR)
WHERE id = LAST_INSERT_ID()
I have got two servers both running a MySQL instance. The first one, server1, is running MySQL 5.0.22. The other one, server2, is running MySQL 5.1.58.
When I create a memory table on server1 and I add a row its size is instantly 8,190.0 KiB.
When I create a memory table on server2 and I add a row its size is still only some bytes, though.
Is this caused by the difference in MySQL version or (hopefully) is this due to some setting I can change?
EDIT:
I haven't found the reason for this behaviour yet, but I did found a workaround. So, for future references, this is what fixed it for me:
All my memory tables are made once and are read-only from thereon. When you specify to MySQL the maximum number of rows your table will have, its size will shrink. The following query will do that for you.
ALTER TABLE table_name MAX_ROWS = N
Factor of 2?
OK, the problem likely is caused by the UTF-8 vs latin1
:- http://dev.mysql.com/doc/refman/5.0/en/storage-requirements.html
You can check the database connection, database default character set for both servers.
here is the testing I have just done :-
mysql> create table test ( name varchar(10) ) engine
-> =memory;
Query OK, 0 rows affected (0.03 sec)
mysql> show create table test;
+-------+------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------+
| test | CREATE TABLE `test` (
`name` varchar(10) DEFAULT NULL
) ENGINE=MEMORY DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> insert into test values ( 1 );
mysql> set names utf8;
Query OK, 0 rows affected (0.01 sec)
mysql> create table test2 ( name varchar(10) ) engine =memory default charset = utf8;
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.01 sec)
mysql> insert into test2 values ( convert(1 using utf8) );
Query OK, 1 row affected (0.01 sec)
mysql> select table_name, avg_row_length from information_schema.tables where TABLE_NAME in( 'test2', 'test');
+------------+----------------+
| table_name | avg_row_length |
+------------+----------------+
| test | 12 |
| test2 | 32 |
+------------+----------------+
2 rows in set (0.01 sec)