I have a table student with field student_id:
S00254
N52145
FG0255
L30211
S20202
ERS4512
I need to get the result like 52145.
Actually my column student_id mixed with character and number need to find
highest value among the rows.
Assuming that every value in your column ends in a five digit number, then the following should work:
SELECT col
FROM yourTable
ORDER BY CAST(RIGHT(col, 5) AS UNSIGNED) DESC
LIMIT 1
VARCHAR maximum row size 65,535 bytes. It can be store 65,535 characters.
learn more https://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html
Mysql version 5.0.3 varchar can store maximum of 65,535 characters.
But again this limit is having limitation of maximum row size which is 65535 bytes. It means including all columns it should be less than 65,535 bytes.
Detailed blog: http://sforsuresh.in/mysql_varchar_max_length/
Related
I've been working with MySQL and very vaguely understand the VARCHAR(This Number Here) part. Is that number the total amount of characters the column can store?
For instance, lets say i have a VARCHAR(400) latin1_general_ci, does the 400 mean a 400 byte limit on the string, or that the string can have 400 characters? How big of a string can i store in that column variable?
This is the maximum string length of the field (see here) (NOT bytes):
The CHAR and VARCHAR types are declared with a length that indicates the maximum number of characters you want to store. For example, CHAR(30) can hold up to 30 characters.
This will allow 30 characters regardless of the encoding.
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 65,535. The effective maximum length of a VARCHAR is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
In contrast to CHAR, VARCHAR values are stored as a 1-byte or 2-byte length prefix plus data. The length prefix indicates the number of bytes in the value. A column uses one length byte if values require no more than 255 bytes, two length bytes if values may require more than 255 bytes.
If I create a column of type VARCHAR (50) on a table and add rows, do the rows actually have 50 characters (or 51 if there's a null-terminating character)? In other words, if I deploy my application and the user input that goes to that column ends up only being strings of no more than 10 characters, am I wasting 80% of memory?
CHARACTER SET
In addition to what is said by the others, the CHARACTER SET for the column needs factoring in.
ascii uses 1 byte for 1 character.
latin1 uses 1 byte for 1 character.
utf8 uses 1, 2, or 3 bytes for 1 character.
utf8mb4 uses 1, 2, 3, or 4 bytes for 1 character.
The number on the declaration is characters, not bytes.
CHAR(10) can hold the widest 10 characters in the given CHARACTER SET. For utf8mb4, it will always occupy 40 bytes. This is a reason to either
never use CHAR, always use VARCHAR, and/or
explicitly say CHARACTER SET ascii for things like Y/N, M/F, country code, postal code, SSN, hex strings, etc.
VARCHAR(10) CHARACTER SET utf8mb4 will handle up to 10 characters, whether it is 1-byte English characters or 3- and 4-byte Chinese characters.
Temp table in a SELECT
A SELECT that does certain things like GROUP BY or ORDER BY or 'UNION' may decide it needs to build a "temp" table for the intermediate processing. If it does, it first considering building the table in RAM using the MEMORY engine. If so, then it turns all VARCHARs into CHARs for the processing. It is vary common to see last_name VARCHAR(255) CHARACTER SET utf8. But when one of these temp tables is used, that becomes 765 bytes per row. This is not very efficient. How often have you seen a last_name that was 255 characters long? So
Don't always use (255); make it something reasonable; and
Use ascii/latin1 when appropriate.
The best way to answer your question is thru comparison.
The CHAR and VARCHAR types are similar, but differ in the way they are stored and retrieved. As of MySQL 5.0.3, they also differ in maximum length and in whether trailing spaces are retained.
For example:
DECLARE CHARARRAY CHAR(30) = 'TEST' -- RESULT IS 'TEST..<30 - 4 SPACES>' (WITH TRAILING SPACES)
on the other hand:
DECLARE VARCHARARRAY VARCHAR(30) = 'TEST' -- RESULT IS 'TEST' (WITHOUT TRAILING SPACES)
The CHAR and VARCHAR types are declared with a length that indicates the maximum number of characters you want to store. For example, CHAR(30) can hold up to 30 characters.
The length of a CHAR column is fixed to the length that you declare when you create the table. The length can be any value from 0 to 255. When CHAR values are stored, they are right-padded with spaces to the specified length. When CHAR values are retrieved, trailing spaces are removed.
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used
In contrast to CHAR, VARCHAR values are stored as a 1-byte or 2-byte length prefix plus data. The length prefix indicates the number of bytes in the value. A column uses one length byte if values require no more than 255 bytes, two length bytes if values may require more than 255 bytes.
Conclusion
If you want to optimize your database, I would suggest you use varchar rather than a char. The sizes of the field may vary depending on field usage. If you are starting to have a design yourself database, this link might help you.
Reference:
The CHAR and VARCHAR Types
I have a MySQL database and I am wondering about the consequences of the varchar size on my query performances.
For example, what would be the difference between a varchar(10) and a varchar(50) in terms of the performances or database size.
If I have something like 10000 rows, would it affect a lot on performances or is it insignificant?
Note : I don't do any join on this column (if that is important)
varchar(10) means that maximum allowed bytes is 10 and varchar(50) means that maximum allowed bytes is 50. Basically, a varchar(10) is no different disk-wise than a varchar(128).So, in whatever manner you declare your columns, it wont make a difference on the storage end. But it will certainly make a difference while making a query.
From the source:
Values in VARCHAR columns are variable-length strings. The length can
be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to
65,535 in 5.0.3 and later versions. The effective maximum length of a
VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size
(65,535 bytes, which is shared among all columns) and the character
set used.
There shouldn't be any real difference in performances between a VARCHAR(10) and VARCHAR(50).
The real difference would be between CHAR and VARCHAR.
http://dev.mysql.com/doc/refman/5.0/en/char.html
The length of a CHAR column is fixed to the length that you declare
when you create the table. The length can be any value from 0 to 255.
When CHAR values are stored, they are right-padded with spaces to the
specified length. When CHAR values are retrieved, trailing spaces are
removed.
Values in VARCHAR columns are variable-length strings. The length can
be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to
65,535 in 5.0.3 and later versions. The effective maximum length of a
VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size
(65,535 bytes, which is shared among all columns) and the character
set used. See Section E.7.4, “Limits on Table Column Count and Row
Size”.
Replacing every VARCHAR by CHAR columns might improve performances, since then, rows will have fixed size, thus reducing fragmentation and somehow optimizing disks access.
That being said, if you have only 10000 rows, I doubt you would see any real difference, unless maybe if you have unusually "long" rows.
I am inserting value
insert into user (name,fbid) Values ('Adi Mathur',100000564553314)
but in the database i see the value if fbid to be
2147483647
Why ? How should i fix it ?
fbid int(50)
As explained in the manual, the maximum value of a (signed) INT, which occupies 4 bytes/32 bits, is 2,147,483,647; for integer data types, the number in parenthesis is the display width, which only affects the way that the data is displayed, not how much space it is allocated for storage:
M indicates the maximum display width for integer types. For floating-point and fixed-point types, M is the total number of digits that can be stored (the precision). For string types, M is the maximum length. The maximum permissible value of M depends on the data type.
You probably want a BIGINT.
What is the maximum range of varchar in MySQL?
I am using the latest version of MySQL and in many sites it is being told that the size is 255. But when i am trying to give a higher size like 500 or 1000, it works for me. So is there a maximum number for varchar datatype?
It was 255 before 5.0.3, but now:
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 65,535.
The documentation of 5.0.x shows the transition:
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions.
The effective maximum length of a VARCHAR is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.
see http://dev.mysql.com/doc/refman/5.1/en/char.html
From the specs
Values in VARCHAR columns are
variable-length strings. The length
can be specified as a value from 0 to
65,535. The effective maximum length
of a VARCHAR is subject to the maximum
row size (65,535 bytes, which is
shared among all columns) and the
character set used.