I previously created a MySQL table and now I want to find out what collation some of the fields are using. What SQL or MySQL commands can I use to discover this?
You could use SHOW FULL COLUMNS FROM tablename which returns a column Collation, for example for a table 'accounts' with a special collation on the column 'name'
mysql> SHOW FULL COLUMNS FROM accounts;
+----------+--------------+-------------------+------+-----+---------+----------+
| Field | Type | Collation | Null | Key | Default | Extra |
+----------+--------------+-------------------+------+-----+---------+----------|
| id | int(11) | NULL | NO | PRI | NULL | auto_inc |
| name | varchar(255) | utf8_bin | YES | | NULL | |
| email | varchar(255) | latin1_swedish_ci | YES | | NULL | |
...
Or you could use SHOW CREATE TABLE tablename which will result in a statement like
mysql> SHOW CREATE TABLE accounts;
CREATE TABLE `accounts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
...
If you want the collation for just that specific column (for possible use with a subquery)...
SELECT COLLATION_NAME
FROM information_schema.columns
WHERE TABLE_SCHEMA = 'tableschemaname'
AND TABLE_NAME = 'tablename'
AND COLUMN_NAME = 'fieldname';
SHOW CREATE TABLE [tablename] will show you the collation of each column as well as the default collation.
Related
This question already has answers here:
MySQL varchar index length
(2 answers)
Closed 1 year ago.
Note:
First I want to mention that I read all other related questions and answers.
Question:
I had created 2 indexes for the table I have but whenever I use my queries it's not using the index. even when forced to use the index it's not using it.
The table has 1.5M rows and it will be increased, and the query is taking 35+ seconds.
Query 1
explain analyze
SELECT sum(cid_user_usd_earned)
FROM `bbtv_adv_records`
WHERE (user_id =2
and `cid_assign_month` = '2020-08-01'
And `content_type` = 'UGC'
);
explain analyze
SELECT sum(cid_user_usd_earned)
FROM `bbtv_adv_records`
USE INDEX (bbtv_adv_records_user_id_cid_assign_month_content_type_index)
WHERE (user_id =2
and `cid_assign_month` = '2020-08-01'
And `content_type` = 'UGC'
);
Query 2
explain analyze
SELECT *
FROM `bbtv_adv_records`
WHERE (user_id =2
and `cid_assign_month` = '2020-08-01'
);
Query 3
explain analyze
SELECT sum(cid_user_usd_earned),channel_id
FROM `bbtv_adv_records`
WHERE (user_id =2
and `cid_assign_month` = '2020-08-01'
Group by `channel_id`
);
Table
CREATE TABLE `bbtv_adv_records` (
`id` bigint UNSIGNED NOT NULL,
`content_type` varchar(400) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
....
`channel_id` varchar(400) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
...
`cid_assign_month` date NOT NULL,
`cid_process_state` enum('process','done','fail') CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
`user_id` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
--
-- Indexes for table `bbtv_adv_records`
--
ALTER TABLE `bbtv_adv_records`
ADD PRIMARY KEY (`id`),
ADD KEY `bbtv_adv_records_user_id_cid_assign_month_index
` (`user_id`,`cid_assign_month`),
ADD KEY `bbtv_adv_records_user_id_cid_assign_month_content_type_index`
(`user_id`,`cid_assign_month`,`content_type`);
--
-- AUTO_INCREMENT for table `bbtv_adv_records`
--
ALTER TABLE `bbtv_adv_records`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=1543191;
COMMIT;
mysql> show index from bbtv_adv_records
+------------------+------------+--------------------------------------------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+------------------+------------+--------------------------------------------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| bbtv_adv_records | 0 | PRIMARY | 1 | id | A | 1456578 | NULL | NULL | | BTREE | | | YES | NULL |
| bbtv_adv_records | 1 | bbtv_adv_records_user_id_cid_assign_month_index | 1 | user_id | A | 8 | NULL | NULL | YES | BTREE | | | YES | NULL |
| bbtv_adv_records | 1 | bbtv_adv_records_user_id_cid_assign_month_index | 2 | cid_assign_month | A | 47 | NULL | NULL | | BTREE | | | YES | NULL |
| bbtv_adv_records | 1 | bbtv_adv_records_user_id_cid_assign_month_content_type_index | 1 | user_id | A | 8 | NULL | NULL | YES | BTREE | | | YES | NULL |
| bbtv_adv_records | 1 | bbtv_adv_records_user_id_cid_assign_month_content_type_index | 2 | cid_assign_month | A | 49 | NULL | NULL | | BTREE | | | YES | NULL |
| bbtv_adv_records | 1 | bbtv_adv_records_user_id_cid_assign_month_content_type_index | 3 | content_type | A | 58 | NULL | NULL | YES | BTREE | | | YES | NULL |
+------------------+------------+--------------------------------------------------------------+--------------+------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
6 rows in set (0.01 sec)
note the best result I have 10 seconds when creating only the cid_assign_month index alone, but all my queries have the cid_assign_month with the user_id always.
could you show the result of "show index from bbtv_adv_records ".
The mysql query optimizer is a cost based optimiser.
It try to find out the best execution plan.
If the cost of ALL( full table scan) is less then REF_OR_NULL (using secondary index fetch data), It will use full table scan where time complexity is O(n) .
for example, there are the commonest cost matrix
the IO cost of Reading 1 block page is 1.
the CPU cost of comparing 1 record is 0.2.
the query 1:
SELECT sum(cid_user_usd_earned) FROM bbtv_adv_records WHERE (user_id =2 and cid_assign_month = '2020-08-01' And content_type = 'UGC');
because the column cid_user_usd_earned is not in secondary index bbtv_adv_records_user_id_cid_assign_month_content_type_index, mysql will return to the primary index to get cid_user_usd_earned, after using binary search in secondary index.
Solved
It looks that MySQL indexing will not work with varchar(400) or any large length.
change from
`content_type` varchar(400) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`channel_id` varchar(400) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`user_id` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
to
`content_type` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`channel_id` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`user_id` bigint UNSIGNED DEFAULT NULL,
now the Query show indexing and faster from 34s to 8s
mysql> explain analyze SELECT sum(cid_user_usd_earned) FROM `bbtv_adv_records` WHERE (user_id =2 and `cid_assign_month` = '2020-08-01' And `content_type` = 'UGC');
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| -> Aggregate: sum(bbtv_adv_records.cid_user_usd_earned) (actual time=8247.975..8247.981 rows=1 loops=1)
-> Index lookup on bbtv_adv_records using bbtv_adv_records_user_id_cid_assign_month_content_type_index (user_id=2, cid_assign_month=DATE'2020-08-01', content_type='UGC') (cost=116370.56 rows=496622) (actual time=0.373..6175.144 rows=259373 loops=1)
|
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (8.25 sec)
I'm using MariaDb server (Ver 15.1 Distrib 10.2.7-MariaDB).
When I execute
CREATE TABLE `my_table` (
`id` INT NOT NULL,
`name` NVARCHAR(64) NULL,
PRIMARY KEY (`id`)
);
Describe output:
MariaDB [db]> describe my_table;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(64) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
Why there is no error, and "name" column datatype is varchar (not nvarchar)?
db schema details:
Default collation: utf8_general_ci
Default characterset: utf8
NVARCHAR is a synonym for VARCHAR in MySQL/MariaDB. But you need to add the CHARACTER SET utf8mb4 to be sure that you get full UTF-8 support.
What you show as the default for that database is only the subset, called 'utf8'. It will not handle Emoji or some of Chinese.
Can I use UTF-8 names in column name on data base? Like example here:
$zapytaj = mysql_query("SELECT * FROM users WHERE `użytkownicy` = '$nazwaużytkownika' ");
This give me error:
Unknown column 'użytkownicy' in 'where clause'
Can someone explain why this is not working?
mysql> SHOW VARIABLES LIKE 'character%';
+--------------------------+-------------
| Variable_name | Value
+--------------------------+-------------
| character_set_client | utf8mb4
| character_set_connection | utf8mb4
| character_set_database | utf8mb4
| character_set_filesystem | binary
| character_set_results | utf8mb4
| character_set_server | latin1
| character_set_system | utf8
mysql> SELECT COLUMN_NAME, HEX(COLUMN_NAME)
FROM information_schema.columns WHERE table_name = "so31349641";
+--------------+--------------------------+
| COLUMN_NAME | HEX(COLUMN_NAME) |
+--------------+--------------------------+
| id | 6964 |
| użytkownicy | 75C5BC79746B6F776E696379 | -- Note the C5BC for ż
| hasło | 686173C5826F | -- and the C582 for ł
+--------------+--------------------------+
If I delete `` from użytkownicy I see this error:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '�ytkownicy = 'xxx'' at line 1
Maybe PHP file are don't have UTF8 coding? How to check this file in PHPStorm?
!SOLUTION!
If You have this error just change mysql to PDO that should fix Your problem.
To answer your stated question, column names are utf8:
mysql> SHOW CREATE TABLE information_schema.columns\G
*************************** 1. row ***************************
Table: COLUMNS
Create Table: CREATE TEMPORARY TABLE `COLUMNS` (
`TABLE_CATALOG` varchar(512) NOT NULL DEFAULT '',
`TABLE_SCHEMA` varchar(64) NOT NULL DEFAULT '',
`TABLE_NAME` varchar(64) NOT NULL DEFAULT '',
`COLUMN_NAME` varchar(64) NOT NULL DEFAULT '', -- NOTE --
`ORDINAL_POSITION` bigint(21) unsigned NOT NULL DEFAULT '0',
`COLUMN_DEFAULT` longtext,
`IS_NULLABLE` varchar(3) NOT NULL DEFAULT '',
`DATA_TYPE` varchar(64) NOT NULL DEFAULT '',
`CHARACTER_MAXIMUM_LENGTH` bigint(21) unsigned DEFAULT NULL,
`CHARACTER_OCTET_LENGTH` bigint(21) unsigned DEFAULT NULL,
`NUMERIC_PRECISION` bigint(21) unsigned DEFAULT NULL,
`NUMERIC_SCALE` bigint(21) unsigned DEFAULT NULL,
`DATETIME_PRECISION` bigint(21) unsigned DEFAULT NULL,
`CHARACTER_SET_NAME` varchar(32) DEFAULT NULL,
`COLLATION_NAME` varchar(32) DEFAULT NULL,
`COLUMN_TYPE` longtext NOT NULL,
`COLUMN_KEY` varchar(3) NOT NULL DEFAULT '',
`EXTRA` varchar(30) NOT NULL DEFAULT '',
`PRIVILEGES` varchar(80) NOT NULL DEFAULT '',
`COLUMN_COMMENT` varchar(1024) NOT NULL DEFAULT ''
) ENGINE=MyISAM DEFAULT CHARSET=utf8
To get to the root of the implied question ("Why does the query fail"), let's see
SHOW VARIABLES LIKE 'character%';
Edit
Well, something un-obvious going on. This works for me:
mysql> create table so31349641 (
id int(11) NOT NULL AUTO_INCREMENT,
użytkownicy varchar(24) NOT NULL,
hasło varchar(24) NOT NULL, PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
mysql> INSERT INTO so31349641 VALUES (1, 'a', 'b');
mysql> SELECT * FROM so31349641 WHERE użytkownicy = 'a';
+----+--------------+--------+
| id | użytkownicy | hasło |
+----+--------------+--------+
| 1 | a | b |
+----+--------------+--------+
This seems ordinary:
mysql> SHOW VARIABLES LIKE 'character%';
+--------------------------+-------------
| Variable_name | Value
+--------------------------+-------------
| character_set_client | utf8
| character_set_connection | utf8
| character_set_database | latin1
| character_set_filesystem | binary
| character_set_results | utf8
| character_set_server | latin1
| character_set_system | utf8
Looking in the IS:
mysql> SELECT COLUMN_NAME, HEX(COLUMN_NAME)
FROM information_schema.columns WHERE table_name = "so31349641";
+--------------+--------------------------+
| COLUMN_NAME | HEX(COLUMN_NAME) |
+--------------+--------------------------+
| id | 6964 |
| użytkownicy | 75C5BC79746B6F776E696379 | -- Note the C5BC
| hasło | 686173C5826F | -- and the C582 for ł
+--------------+--------------------------+
That is as I would expect it.
My char% values are different than yours, but I think we are both "OK" for this situation.
Try a SELECT on the information_schema similar to what I did.
Next, what is your client? PHP? Something else? Perhaps the encoding is incorrect in the client.
(Rather than trying to use HTML tags in a Comment, Edit your original question with the added info.)
It looks like UTF-8 in SQL is not default, but tables/databases can be changed to be so.
Some potentially helpful links:
The mySQL documentation on charsets:
https://dev.mysql.com/doc/refman/5.0/en/charset.html
A SO question on determining the charset:
determining the character set of a table / database?
On changing the charset: http://makandracards.com/makandra/2529-show-and-change-mysql-default-character-set
Hope this helps.
I have created one temporary table named "table1". I am trying to list the columns of my temp table. I am not getting any values. Here is my mysql query.
SELECT column_name
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'table2';
Any body help me please?
Thanks
You cannot get the temporary table columns using the INFORMATION_SCHEMA
The only way which you can use is to go with SHOW CREATE TABLE table2
"INFORMATION_SCHEMA.COLUMNS" does not contains columns of temporary table.
You can use SHOW COLUMS to achieve this.
Example Table:
CREATE TEMPORARY TABLE SalesSummary (
product_name VARCHAR(50) NOT NULL,
total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00,
avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00,
total_units_sold INT UNSIGNED NOT NULL DEFAULT 0
);
Command:
SHOW COLUMNS FROM SalesSummary;
Outout:
mysql> SHOW COLUMNS FROM SalesSummary;
+------------------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------+------------------+------+-----+---------+-------+
| product_name | varchar(50) | NO | | NULL | |
| total_sales | decimal(12,2) | NO | | 0.00 | |
| avg_unit_price | decimal(7,2) | NO | | 0.00 | |
| total_units_sold | int(10) unsigned | NO | | 0 | |
+------------------+------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
More details are in the manual Section 13.7.5.5 for MySQL 5.7. Link
Another possibility is using SHOW CREATE TABLE:
mysql> SHOW CREATE TABLE SalesSummary\G
*************************** 1. row ***************************
Table: SalesSummary
Create Table: CREATE TEMPORARY TABLE `SalesSummary` (
`product_name` varchar(50) NOT NULL,
`total_sales` decimal(12,2) NOT NULL DEFAULT '0.00',
`avg_unit_price` decimal(7,2) NOT NULL DEFAULT '0.00',
`total_units_sold` int(10) unsigned NOT NULL DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
Here are some more details.
In Mysql 5.7 there is a seperate table called INNODB_TEMP_TABLE_INFO to achieve this.
It is possible to get a list of column names for any table.
This method will also work for TEMPORARY tables:
SET #columns_string = ''
;
SHOW
COLUMNS
FROM
`mysql`.`user`
WHERE
#columns_string := CONCAT(`Field`, ',', #columns_string)
;
SELECT #columns_string
;
#columns_string will have a value of:
account_locked,password_lifetime,password_last_changed,password_expired,authentication_string,plugin,max_user_connections,max_connections,max_updates,max_questions,x509_subject,x509_issuer,ssl_cipher,ssl_type,Create_tablespace_priv,Trigger_priv,Event_priv,Create_user_priv,Alter_routine_priv,Create_routine_priv,Show_view_priv,Create_view_priv,Repl_client_priv,Repl_slave_priv,Execute_priv,Lock_tables_priv,Create_tmp_table_priv,Super_priv,Show_db_priv,Alter_priv,Index_priv,References_priv,Grant_priv,File_priv,Process_priv,Shutdown_priv,Reload_priv,Drop_priv,Create_priv,Delete_priv,Update_priv,Insert_priv,Select_priv,User,Host,
The problem with this solution (besides needing to parse a string) is that the SHOW COLUMNS command will always generate an (empty) resultset.
This means that you can't really use this method in a stored procedure that returns a SELECT (you will end up with more than one resultset).
Edit: Not sure why this is marked as a duplicate. The error I am getting is different
I am trying to remove a primary key definition but am receiving an error for some reason.
mysql> ALTER TABLE `aux_sponsors` DROP PRIMARY KEY;
ERROR 1091 (42000): Can't DROP 'PRIMARY'; check that column/key exists
mysql> desc aux_sponsors;
+-------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+-------+
| unit | varchar(8) | NO | | MF | |
| code | varchar(32) | NO | PRI | NULL | |
| userid | varchar(32) | NO | | | |
| fullName | varchar(64) | NO | | | |
| department | varchar(255) | NO | | | |
| description | varchar(255) | NO | | NULL | |
+-------------+--------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
Am I doing something wrong here? I simply want no more primary key in this table.
mysql> SHOW CREATE TABLE aux_sponsors;
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| aux_sponsors | CREATE TABLE `aux_sponsors` (
`unit` varchar(8) NOT NULL DEFAULT 'MF',
`code` varchar(32) NOT NULL,
`userid` varchar(32) NOT NULL DEFAULT '',
`fullName` varchar(64) NOT NULL DEFAULT '',
`department` varchar(255) NOT NULL DEFAULT '',
`description` varchar(255) NOT NULL,
UNIQUE KEY `code` (`code`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+--------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
You don't have a PRIMARY KEY; you have a UNIQUE key. So, you can't do this:
ALTER TABLE `aux_sponsors` DROP PRIMARY KEY
Instead, just do
ALTER TABLE `aux_sponsors` DROP KEY `code`
DESC (a/k/a DESCRIBE) is not a true MySQL feature; according to the docs, "The DESCRIBE statement is provided for compatibility with Oracle."
More from the documentation:
A UNIQUE index may be displayed as PRI if it cannot contain NULL values and there is no PRIMARY KEY in the table. A UNIQUE index may display as MUL if several columns form a composite UNIQUE index; although the combination of the columns is unique, each column can still hold multiple occurrences of a given value.
In your case, the column code is NOT NULL and is the only column in a UNIQUE key, so DESC is showing it as PRI. Because of this type of problem, it's better to use SHOW INDEX to find out the types of keys on a table.