I read that you can specify the max limit of int to be 11. Why is this if in 4294967295 there are only 10 digits?
It is the "display width", not the maximum storage size. That means it can take ten characters to write the digits and perhaps one character for a minus sign in the negative case, so 11 characters are the most necessary to write the integer.
For more info, see:
http://waynewhitty.ie/blog-post.php?id=19
and
https://blogs.oracle.com/jsmyth/entry/what_does_the_11_mean
Related
Why do we have the limitation on datatypes like Char and varchar etc. but not on Integer ?
Why its designed in such a way ?
Eg:
We can define char(8), but we cannot define Int(8) or integer(8). It would have a max of 11 characters saved for it.
Integer have a fixed size of bytes 1-8, depending which kind you have defined.
char has a fixed size of bytes per character so you defined the size of 8 character you get 8 times the size if the character.
As it makes no sense to limit that fixed size if bytes, mysqkl finally kicked it out(in future) and gives now a warning, when you create a integer with a size
I was reading the mysql documentation on the byte size for different data types, but was a little confused when it came to char, varchar and decimal.
Can somebody help explain the bytes for these three data types, and also answer how many bytes for the following:
char(7)
varchar(9)
decimal(15,2)
decimal(11,6)
Thanks
CHAR(N) is probably the most confusing because a char is not a fixed byte size across character sets. Furthermore, different row formats handle this problem differently. Tersely, if you're using ROW_FORMAT=COMPACT, ROW_FORMAT=DYNAMIC or ROW_FORMAT=COMPRESSED then CHAR(N) reverse a minimum of N bytes in order to achieve updates in place without fragmentation. If more bytes are required as the result of a different character encoding than it will use more as necessary, trying to use as few as possible, and NO MORE than the maximum character byte length * N is used. If you're using ROW_FORMAT=REDUNDANT, than CHAR(N) always uses the maximum character byte length * N.
VARCHAR(N) and VARBINARY(N) sets a maximum character length per column of N. Below N, MySQL uses the number of bytes required given the string and character encoding used. MySQL then uses one additional byte to record the length of the string if the string is below 256 bytes. If the length of the string is greater than 255 bytes than it uses 2 bytes to record the length of the string. VAR columns are storage efficient but for string columns with frequent UPDATES, one can trade storage for performance by using a fixed length column such as BINARY.
The DECIMAL description is pretty self explanatory:
"Values for DECIMAL (and NUMERIC) columns are represented using a binary format that packs nine decimal (base 10) digits into four bytes. Storage for the integer and fractional parts of each value are determined separately. Each multiple of nine digits requires four bytes, and the “leftover” digits require some fraction of four bytes. The storage required for excess digits is given by the following table"
I'm using MySQL, all my tables are using InnoDB engine. I have some columns declared as DECIMAL(38, 0) and they are used extensively. According to the MySQL documentation (http://dev.mysql.com/doc/refman/5.5/en/storage-requirements.html), 38-digit value requires 17 bytes (38 = 4 * 9 + 2; 4 * 4 + 1 = 17). Okay.
But, does that mean that any value stored in this column will take 17 bytes? For example, for value 432 - will it take 4 bytes only (I really hope so...) or will it take 17 bytes anyway?
Finally, I know that in Oracle the size occupied depends on the actual values stored. But is it optimized that way in MySQL as well?
I think the answer is that it will take 17 bytes anyway. If you notice, detailed in the linked manual page there is no means for the DBMS to record how "long" the value is. By comparison, for a VARCHAR(255) CHARACTER SET ascii column there is a single byte at the start of the value that indicates how long the value is (for a maximum size of 256 bytes). For a VARCHAR(1000) CHARACTER SET ascii column there are two bytes to indicate the length. Here no means is detailed to record the length of the value, leading me to conclude that the column always takes the maximum amount of space.
Decimal is "fixed length" so every value requires 17 bytes
I always thought INT(5) means a number which has a max size of 5 digits. I tried entering a huge number inside it and it somehow got cut down to 2147483647
This obviously isnt 5 digits. So what does INT(5) have a limitation of ?
From MySQL Docs, Numeric Type Attributes
MySQL supports an extension for optionally specifying the display width of integer data types in parentheses following the base keyword for the type. For example, INT(4) specifies an INT with a display width of four digits. This optional display width may be used by applications to display integer values having a width less than the width specified for the column by left-padding them with spaces. (That is, this width is present in the metadata returned with result sets. Whether it is used or not is up to the application.)
INT is always four bytes wide. The 5 is the "display width".
In MySQL, INT(5) does not mean that values are limited to 5-character values. It only means that MySQL will try to pad these values with spaces/zeroes when returning them.
The numeric range of any signed INT including INT(10), INT(5) or any other INT(n) is:
-2,147,483,648 ... 2,147,483,647, which is 10 digits at most.
http://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html
"M indicates the maximum display width for integer types. The maximum legal display width is 255. Display width is unrelated to the range of values a type can contain, as described in Section 10.2, “Numeric Types”"
https://alexander.kirk.at/2007/08/24/what-does-size-in-intsize-of-mysql-mean/
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. For string types, M is the maximum length. The maximum allowable value of M depends on the data type.
An int can be between -2147483648 and 2147483647 signed, or 0 and 4294967295 unsigned.
Thats why it was cut down to that if you entered a number larger than it as a signed value
A very common misconception about what int(N) means in MySQL is that the column can store maximum integer value with N digits in length. However, this is not true. int(N) does not determines the maximum value that the column can store in it. N is the display width of the integer column, unlike the characters columns where the number means number of character that can be stored.
The number in the parenthesis does not determines the max and min values that can be stored in the integer field. The max and min values that can be stored are always fixed. The following table shows the required storage and range for each integer type.
If TINYINT can store three characters, for example, why can't it store up to the number 999?
Because it takes only 8 bit and hence can encode no more than 2^8 = 256 values.
The three characters you see in something like '123' are the result of the binary to decimal conversion. You cannot store arbitrary 3 characters there.
It is 8 bits and can actually store a maximum value of 255. 8 bits have 256 possible states including zero.