I am trying to change the collation on a bunch of columns. I don't want to mess up my current data, so I've been looking at doing something like in this answer:
ALTER TABLE something MODIFY name BLOB;
The next step is to convert the column to a nonbinary data type with the proper character set:
ALTER TABLE something MODIFY name VARCHAR(12) CHARACTER SET hebrew COLLATE hebrew_bin;
Or Try with this:
ALTER TABLE something MODIFY name VARCHAR(12) CHARACTER SET utf8 COLLATE utf8_unicode_ci
Unfortunately, mysql won't let me convert an indexed column to a blob.
SQL error: [1170] - BLOB/TEXT column 'baz' used in key specification without a key length
Query: ALTER TABLE foo.bar MODIFY baz blob;
Is there a way around this? Or do I need to somehow remove my indexes and rebuild them after the conversion?
Don't do the "2-step ALTER" unless the CHARACTER SET was wrong but the data was 'right'. If you want to convert both the CHARACTER SET and the data, use
ALTER TABLE something CONVERT TO CHARACTER SET ...;
See Case 5 in my blog, which, as you might guess, has other cases.
As for the error 1170 -- that had to do with some INDEX. Before I help you with that, decide whether it is relevant.
Related
So I'm using a wrapper to fetch user data from instagram. I want to select the display names for users, and store them in a MYSQL database. I'm having issues inserting some of the display names, dealing with, specifically, an incorrect string value error:
Now, I've dealt with this issue before with accent marks, letters with umlauts, etc. The solution would be to change the collation to utf8_general_ci under the utf8 charset.
So as you can see, some of the display names I'm pulling have very unique characters that I'm not sure mySQL can recognize at all, i.e.:
แ๐ฐ๐๐๐๐ ๐พ๐๐๐๐๐๐๐๐ยฎ
So I receive:
Error Code: 1366. Incorrect string value: '\xF0\x9D\x99\x87\xF0\x9D...' for column 'dummy' at row 1
Here's my sql code
CREATE TABLE test_table(
id INT AUTO_INCREMENT,
dummy VARCHAR(255),
PRIMARY KEY(id)
);
INSERT INTO test_table (dummy)
VALUES ('แ๐ฐ๐๐๐๐ ๐พ๐๐๐๐๐๐๐๐ยฎ');
Any thoughts on a proper charset + collation pair that can handle characters like this? Not sure where to look for a solution, so I come here to see if anyone dealt with this.
P.S., I've tried utf8mb4 charset with utf8mb4_unicode_ci and utf8mb4_bin collations as well.
The characters you show require the column use the utf8mb4 encoding. Currently it seems your column is defined with the utf8mb3 encoding.
The way MySQL uses the name "utf8" is complicated, as described in https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb3.html:
Note
Historically, MySQL has used utf8 as an alias for utf8mb3;
beginning with MySQL 8.0.28, utf8mb3 is used exclusively in the output
of SHOW statements and in Information Schema tables when this
character set is meant.
At some point in the future utf8 is expected to become a reference to
utf8mb4. To avoid ambiguity about the meaning of utf8, consider
specifying utf8mb4 explicitly for character set references instead of
utf8.
You should also be aware that the utf8mb3 character set is deprecated
and you should expect it to be removed in a future MySQL release.
Please use utf8mb4 instead.
You may have tried to change your table in the following way:
ALTER TABLE test_table CHARSET=utf8mb4;
But that only changes the default character set, to be used if you add new columns to the table subsequently. It does not change any of the current columns. To do that:
ALTER TABLE test_table MODIFY COLUMN dummy VARCHAR(255) CHARACTER SET utf8mb4;
Or to convert all string or TEXT columns in a table in one statement:
ALTER TABLE test_table CONVERT TO CHARACTER SET utf8mb4;
That would be ๐ - L MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL L
It requires the utf8mb4 Character set to even represent it. "F0" is the clue; it is the first of 4 bytes in a 4-byte UTF-8 character. It cannot be represented in MySQL's "utf8". Collation is (mostly) irrelevant.
Most, not all, of the characters in แ๐ฐ๐๐๐๐ ๐พ๐๐๐๐๐๐๐๐ยฎ also need utf8mb4. They are "MATHEMATICAL BOLD FRAKTUR" letters.
(Meanwhile, Bill gives you more of an answer.)
I will have to convert the database encoding from latin-1 to utf-8.
I'm aware of the fact that converting the database is done via the command of
ALTER DATABASE db_name
[[DEFAULT] CHARACTER SET charset_name]
[[DEFAULT] COLLATE collation_name]
Source and converting an existing table is done via the command of
ALTER TABLE tbl_name
[[DEFAULT] CHARACTER SET charset_name]
[COLLATE collation_name]
Source.
However, the database is already existent and there is sensitive information involved. My question is whether the data I already have will be changed. The purpose of this question is that I have to give an estimate before I do the change.
Every (character string-type) column has its own character set and collation metadata.
If, when the column's data type was specified (i.e. when it was last created or altered), no character set/collation was explicitly given, then the table's default character set and collation would be used for the column.
If, when the table was specified, no default character set/collation was explicitly given, then the database's default character set and collation would be used for the table's default.
The commands that you quote in your question merely alter such default character sets/collations for the database and table respectively. In other words, they will only affect tables and columns that are created thereafterโthey will not affect existing columns (or data).
To update existing data, you should first read the Changing the Character Set section of the manual page on ALTER TABLE:
Changing the Character Set
To change the table default character set and all character columns (CHAR, VARCHAR, TEXT) to a new character set, use a statement like this:
ALTER TABLE tbl_name CONVERT TO CHARACTER SET charset_name;
The statement also changes the collation of all character columns. If you specify no COLLATE clause to indicate which collation to use, the statement uses default collation for the character set. If this collation is inappropriate for the intended table use (for example, if it would change from a case-sensitive collation to a case-insensitive collation), specify a collation explicitly.
For a column that has a data type of VARCHAR or one of the TEXT types, CONVERT TO CHARACTER SET changes the data type as necessary to ensure that the new column is long enough to store as many characters as the original column. For example, a TEXT column has two length bytes, which store the byte-length of values in the column, up to a maximum of 65,535. For a latin1 TEXT column, each character requires a single byte, so the column can store up to 65,535 characters. If the column is converted to utf8, each character might require up to three bytes, for a maximum possible length of 3 ร 65,535 = 196,605 bytes. That length does not fit in a TEXT column's length bytes, so MySQL converts the data type to MEDIUMTEXT, which is the smallest string type for which the length bytes can record a value of 196,605. Similarly, a VARCHAR column might be converted to MEDIUMTEXT.
To avoid data type changes of the type just described, do not use CONVERT TO CHARACTER SET. Instead, use MODIFY to change individual columns. For example:
ALTER TABLE t MODIFY latin1_text_col TEXT CHARACTER SET utf8;
ALTER TABLE t MODIFY latin1_varchar_col VARCHAR(M) CHARACTER SET utf8;
If you specify CONVERT TO CHARACTER SET binary, the CHAR, VARCHAR, and TEXT columns are converted to their corresponding binary string types (BINARY, VARBINARY, BLOB). This means that the columns no longer will have a character set attribute and a subsequent CONVERT TO operation will not apply to them.
If charset_name is DEFAULT in a CONVERT TO CHARACTER SET operation, the character set named by the character_set_database system variable is used.
ย Warning
The CONVERT TO operation converts column values between the original and named character sets. This is not what you want if you have a column in one character set (like latin1) but the stored values actually use some other, incompatible character set (like utf8). In this case, you have to do the following for each such column:
ALTER TABLE t1 CHANGE c1 c1 BLOB;
ALTER TABLE t1 CHANGE c1 c1 TEXT CHARACTER SET utf8;
The reason this works is that there is no conversion when you convert to or from BLOB columns.
To change only the default character set for a table, use this statement:
ALTER TABLE tbl_name DEFAULT CHARACTER SET charset_name;
The word DEFAULT is optional. The default character set is the character set that is used if you do not specify the character set for columns that you add to a table later (for example, with ALTER TABLE ... ADD column).
When the foreign_key_checks system variable is enabled, which is the default setting, character set conversion is not permitted on tables that include a character string column used in a foreign key constraint. The workaround is to disable foreign_key_checks before performing the character set conversion. You must perform the conversion on both tables involved in the foreign key constraint before re-enabling foreign_key_checks. If you re-enable foreign_key_checks after converting only one of the tables, an ON DELETE CASCADE or ON UPDATE CASCADE operation could corrupt data in the referencing table due to implicit conversion that occurs during these operations (Bug #45290, Bug #74816).
I am trying to convert the charset of a TEXT column in a huge production database from utf8 to utf8mb4 to support emojis.
I have read that for varchar columns we need to calculate and provide a different size in the alter command. But I couldn't find anything about TEXT columns.
TEXT columns are stored off the table so can I go ahead with the alter command or is there anything to be considered?
Not a problem.
The "different size" may refer to changing VARCHAR(255) to VARCHAR(191) to fit within the 767 byte limit for indexes. That is not relevant for TEXT.
How ere you planning on doing the conversion? I think (but have not tested) this will work:
ALTER TABLE tbl CONVERT TO CHARACTER SET utf8mb4;
I have a table with a unique constraint on a varchar field. When I try to insert 'e' and 'ั' in two different rows I'm prompted with a unique constraint violation. Executing the following select shows that MySQL considers the letters equivalent in spite of their HEX values being D0B5 and D191 respectively.
select 'ะต' = 'ั',
hex('ะต'),
hex('ั');
Following a fair amount of Googling I came across this MySQL bug report which seems to deal with this issue. The very last response by Sveta Smirnova states that this behavior is by design and refers to the Collation chart for utf8_unicode_ci, European alphabets (MySQL 6.0.4).
How do I tell MySQL that 'ะต' is not equal to 'ั' for query purposes and how do I change the unique constraint to take note of this fact?
You may wish to check this answer: Is it possible to remove mysql table collation?
The behavior you're seeing is standard. In most cases it produces the best results. From a point of interest do you have an example of how this is causing a problem for you. Have you found two words which match except for the diacritic?
Either way the only thing you can do about it is to change the collation. This can be done at the server, database, table or even field level.
Rather than my duplicating the manual on how to do this; please follow this link: http://dev.mysql.com/doc/refman/5.7/en/charset-syntax.html
There's a listing here of the different collations supported: http://dev.mysql.com/doc/refman/5.5/en/charset-charsets.html
If you need that for an especific field you could add a duplicate of the column with a different collation for prevent this issue.
ALTER TABLE yourTable ADD COLUMN `copiedColumn` VARCHAR(100) CHARACTER SET 'binary' COLLATE 'binary';
Also, you can change the collation of your column if you don't need the your current collation in this field
ALTER TABLE yourTable CHANGE COLUMN yourColumn yourColumn VARCHAR(100) CHARACTER SET 'binary' COLLATE 'binary';
I'm writing a set of SQL statements in MySQL to create and modify a few tables. I need to get my output to match a document of sample output exactly (this is for school).
When I show my create table statements, all varchar columns need to look like this:
`name` varchar(10) COLLATE utf8_unicode_ci DEFAULT NULL,
but they weren't showing the collation. I tried changing the declaration to
name varchar COLLATE utf8_unicode_ci DEFAULT NULL,
but this caused the output to show both the charset and collation, and I need to be showing just the collation. The sample output document was created on Unix, while I am on Windows, so this could be the source of the difference, but I need to know for sure.
Is there a way I can alter my queries to show collation or is this just a Unix Windows inconsistency?
To be honest, I doubt very much that anyone intends for you to obtain output that is identical verbatemโit's more likely that they require it to be identical semantically. However, you might play around with the table's default charset/collation to see whether that makes a difference to the output obtained from SHOW CREATE TABLE:
ALTER TABLE foo CHARACTER SET utf8 COLLATE ut8_bin;
Failing that, it could be a difference between MySQL versions.