I want to limit usernames to 16 characters long.
I thought this would work:
create table user(id int unsigned auto_increment not null, username tinytext(16) not null, primary key (id));
but it doesn't
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 '(16) not null, primary key (id))' at line 1
That is what varchar() is for:
create table user(
id int unsigned auto_increment not null,
username varchar(16) not null,
primary key (id)
);
Review syntax of data types here: https://dev.mysql.com/doc/refman/5.7/en/string-type-overview.html
TINYTEXT does not accept a length argument.
TEXT does accept a length argument, but it doesn't do what you think it does. It just changes the data type to one of the flavors of TEXT that is the smallest type that will allow at least the length you request.
As stated in the manual page:
An optional length M can be given for this type. If this is done, MySQL creates the column as the smallest TEXT type large enough to hold values M characters long.
So TEXT(16) will create the column as TINYTEXT because that's the least of the family of TEXT types that will hold strings of length 16. Another example is if you specify TEXT(2000000), it would promote the column to MEDIUMTEXT.
mysql> create table t ( t1 text(16), t2 text(2000000) );
Query OK, 0 rows affected (0.04 sec)
mysql> show create table t\G
*************************** 1. row ***************************
Table: t
Create Table: CREATE TABLE `t` (
`t1` tinytext,
`t2` mediumtext
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
Notice the columns have automatically been changed, and they no longer have length specifiers.
This means the TINYTEXT column will still allow up to 255 bytes, and the MEDIUMTEXT column will allow up to 16MB. The text length specified is not a limit, but a guideline for which type is needed.
If you really want to limit inputs to 16 characters, then use VARCHAR(16).
Related
Let's say we have a simple table of 2 columns with two scenarios.
With ID column of length 10
CREATE TABLE `members` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(50) NOT NULL,
)
With ID column of length 1
CREATE TABLE `members` (
`id` int(1) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(50) NOT NULL,
)
Can I define the length of column ID by 1 if I don't need the leading zeros in the ID column?
I don't have an idea where the leading zeros are helpful and what are the cons if I define the length of the integer column by 1 if there is no need for leading zeros.
If you don't need leading zeroes, then simply do not use the ZEROFILL column option, which I see is already absent from your create table statement.
The "length" of an integer is meaningless except for display. It does not affect the storage size of the integer, or the maximum value that can be stored in it. The length is optional, and I always omit it.
Example:
CREATE TABLE `members` (
`id` int unsigned NOT NULL AUTO_INCREMENT,
...
This has been the source of confusion for MySQL users for many years.
Finally in MySQL 8.0, they stopped outputting this misleading syntax when you use SHOW CREATE TABLE. Use of the integer length is discouraged.
The short answer is: You can set the zerofill length to 1 if you absolutely have no use of it. However, sometimes you may want your numbers to be neatly aligned . e.g Instead of displaying ID values from 1 all the way up to 9999, defining an int(4) zerofill makes the values show up from 0001 to 9999. That could be helpful in certain formal scenarios.
It seems like a bug because when I set the integer value on a column it says it has been changed successfully but nothing happens and the integer value remains blank.
I can't use the database because I get the error that all my integer columns have incorrect integer values, but when I try to change them to int(11) e.g. nothing is happening.
Does anyone know how to fix this?
I can set columns with varchar datatypes to have values and they work fine.
Fatal error: Uncaught mysqli_sql_exception: Incorrect integer value: '' for column 'topic_id' at row 1 in C:\wamp64\www\mycode\upload2.php on line 32
mysqli_sql_exception: Incorrect integer value: '' for column 'topic_id' at row 1 in C:\wamp64\www\mycode\upload2.php on line 32
Code:
ALTER TABLE `topics` CHANGE `topic_id` `topic_id` INT(11) NOT NULL
AUTO_INCREMENT;
// This isn't changing the int value at all!
You have multiple errors in what you are attempting to do.
First, there is the problem that the values in the table are not integers.
Second, you cannot set a column to auto-increment unless it is the primary key.
One option is to drop the primary key and auto-increment idea. Then you can update the values to NULL and change the column to an int:
update topics
set topic_id = null
where topic_id regexp '[^0-9]';
ALTER TABLE `topics` CHANGE `topic_id` `topic_id` INT(11) ;
Here is a db<>fiddle.
If you really want topic_id to be an auto-increment primary key, then I would suggest recreating the table. Something like this:
create table temp_topics as
select *
from topics;
drop table topics; -- be very careful here!
create table topics (
topic_id int auto_increment primary key,
. . . -- the rest of the columns
);
insert into topics (<list of columns here>)
select <list of columns here>
from temp_topics;
if you wanna change a value you have to update that row.
what you are trying to do is wrong , int data type has fixed length (4 bytes), so when you give it a length , it actually doesn't mean anything and its been ignored by the sql engine
see MySql Ref: https://dev.mysql.com/doc/refman/8.0/en/integer-types.html
numeric data types are divided into 3 categoies :
Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT
Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC
Floating-Point Types (Approximate Value) - FLOAT, DOUBLE
CREATE TABLE IF NOT EXISTS `test` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`country` varchar(5) NOT NULL,
`state` char(5) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
I tried following query to insert data
INSERT INTO `test`.`test` (`id` ,`country` ,`state`)
VALUES (NULL , 'south-india', 'Gujarat');
When I execute above query It will shows following warning
Warning: #1265 Data truncated for column 'country' at row 1
Warning: #1265 Data truncated for column 'state' at row 1
I found Reference that VARCHAR is variable-length.CHAR is fixed length.
Then what you mean by
VARCHAR is variable-length.
CHAR is fixed length.
VARCHAR(5) will use at most 5 characters of storage, while CHAR(5) will always use exactly 5.
For a field holding a person's name, for example, you'd want to use a VARCHAR, because while on average someone's name is usually short, you still want to cope with the few people with very long names, without having to have that space wasted for the majority of your database rows.
As you said varchar is variable-length and char is fixed. But the main difference is the byte it uses.
Example.
column: username
type: char(10)
if you have data on column username which is 'test', it will use 10 bytes. and it will have space.
'test______'
Hence the varchar column will only uses the byte you use. for 'test' it will only use 4 bytes. and your data will be
'test'
THanks.
As you mentioned VARCHAR is variable-length. CHAR is fixed length.
when you say
Varchar(5) and if the data you store in it is of length 1, The
remaining 4 byte memory space will be used by others. example: "t"
on the other hand
Char(5) and if the data you store in it is of length 1, The remaining
4 byte memory space cant be used. The 4 byte will end up not used by
any other data. example: "t____" here ____ is the unused space.
I have a table created like so:
CREATE TABLE `my_table` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`info` varchar(50) DEFAULT NULL,
`some_more_info` smallint(5) unsigned NOT NULL
PRIMARY KEY (`id`),
KEY `my_index` (`some_more_info`,`info`(24)),
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8
My question is about the second key called my_index. What does the "(24)" size limit mean? The actual size of the column is 50, but the index is only 24 characters.
Does this mean that MySQL indexes only the first 24 characters of the column info?
In short, yes, the first 24 characters are taken into consideration to build the BTree index. Indexing limits are assigned to text types such as varchar and text, as they don't affect numeric precision.
Yes.
The entire description about the index length can be found here:
http://dev.mysql.com/doc/refman/5.0/en/create-index.html
Prefix lengths are given in characters for nonbinary string types and
in bytes for binary string types. That is, index entries consist of
the first length characters of each column value for CHAR, VARCHAR,
and TEXT columns, and the first length bytes of each column value for
BINARY, VARBINARY, and BLOB columns.
Also you create query has/had some extra ,'s.
I inserted some info into my mysql database and I got the following error listed below. What does this mean and how can I fix it?
1 row(s) inserted.
Inserted row id: 1
Warning: #1265 Data truncated for column 'summary' at row 1
Here is my Mysql tables structure below.
CREATE TABLE mem_articles (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
member_id INT UNSIGNED NOT NULL,
title VARCHAR(255) NOT NULL,
summary VARCHAR(255) DEFAULT NULL,
content LONGTEXT NOT NULL,
date_created DATETIME NOT NULL,
date_updated DATETIME DEFAULT NULL,
PRIMARY KEY (id)
);
I think it means that the amount of characters you attempted to insert into the summary column exceeded 255, perhaps you should alter it to be TEXT instead of VARCHAR(255).
http://dev.mysql.com/doc/refman/5.1/en/alter-table.html
It means that the data were "truncated", which in MySQL terminology means either it was truncated, or it was changed into something totally different if it was incompatible with the type.
This behaviour sucks; if you don't want it, use
SET SQL_MODE='TRADITIONAL'
Then it will behave like a sensible database (unfortunately this will probably break your entire code base if it's an existing application)
I would suggest setting the type to "longtext" or something larger.