MySQL Performance: Indexing and Why We Do It?
This is a relatively short post on MySQL indexing, why we do it, what it’s advantages are, were the caveats lie and we you should study it. In this article I will cover two main indexing methods, these being the Berkeley BTREE and the HASH indexing methods.
Lets start!
When you’re designing database tables, the first thing you want to remember is that the smaller the footprint the better the storage ability and larger the dataset without it slowing down.
However, caveat one:
When designing Database table, its the columns that should be efficient, not having indexes will make your database table’s footprint overall smaller but it wont be as efficient!
The first thing we need to understand is column byte sizes and what they are used for, here is a table of columns available in a standard INNODB engine table:
| Type |
Use for |
Size |
| TINYINT |
A very small integer |
The signed range is –128 to 127. The unsigned range is 0 to 255. |
| SMALLINT |
A small integer |
The signed range is –32768 to 32767. The unsigned range is 0 to 65535 |
| MEDIUMINT |
A medium-size integer |
The signed range is –8388608 to 8388607. The unsigned range is 0 to 16777215 |
| INT or INTEGER |
A normal-size integer |
The signed range is –2147483648 to 2147483647. The unsigned range is 0 to 4294967295 |
| BIGINT |
A large integer |
The signed range is –9223372036854775808 to 9223372036854775807. The unsigned range is 0 to 18446744073709551615 |
| FLOAT |
A small (single-precision) floating-point number. Cannot be unsigned |
Ranges are –3.402823466E+38 to –1.175494351E-38, 0 and 1.175494351E-38 to 3.402823466E+38. If the number of Decimals is not set or <= 24 it is a single-precision floating point number |
| DOUBLE, DOUBLE PRECISION, REAL |
A normal-size (double-precision) floating-point number. Cannot be unsigned |
Ranges are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0 and 2.2250738585072014E-308 to 1.7976931348623157E+308. If the number of Decimals is notset or 25 <= Decimals <= 53 stands for a double-precision floating point number
|
| DECIMAL, NUMERIC |
An unpacked floating-point number. Cannot be unsigned |
Behaves like a CHAR column: “unpacked” means the number is stored as a string, using one character for each digit of the value. The decimal point, and, for negative numbers, the ‘–‘ sign is not counted in Length. If Decimals is 0, values will have no decimalpoint or fractional part. The maximum range of DECIMAL values is the same as
for DOUBLE, but the actual range for a given DECIMAL column may be constrained by the choice of Length and Decimals. If Decimals is left out it’s set to 0. If Length is left out it’s set to 10. Note that in MySQL 3.22 the Length includes the sign and the decimal point
|
| DATE |
A date |
The supported range is ‘1000-01-01’ to ‘9999-12-31’. MySQL displays DATE values in ‘YYYY-MM-DD’ format |
| DATETIME |
A date and time combination |
The supported range is ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’. MySQL displays DATETIME values in ‘YYYY-MM-DD HH:MM:SS’ format |
| TIMESTAMP |
A timestamp |
The range is ‘1970-01-01 00:00:00’ to sometime in the year 2037. MySQL displays TIMESTAMP values in YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD or YYMMDD format, depending on whether M is 14 (ormissing), 12, 8 or 6, but allows you to assign values to TIMESTAMP columns using
either strings or numbers. A TIMESTAMP column is useful for recording the date and time of an INSERT or UPDATE operation because it is automatically set to the date and time of the most recent operation if you don’t give it a value yourself
|
| TIME |
A time |
The range is ‘-838:59:59’ to ‘838:59:59’. MySQL displays TIME values in ‘HH:MM:SS’ format, but allows you to assign values to TIME columns using either strings or numbers |
| YEAR |
A year in 2- or 4- digit formats (default is 4-digit) |
The allowable values are 1901 to 2155, and 0000 in the 4 year format and 1970-2069 if you use the 2 digit format (70-69). MySQL displays YEAR values in YYYYformat, but allows you to assign values to YEAR columns using either strings or
numbers. (The YEAR type is new in MySQL 3.22.)
|
| CHAR |
A fixed-length string that is always right-padded with spaces to the specified length when stored |
The range of Length is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. CHAR values are sorted and compared in case-insensitivefashion according to the default character set unless the BINARY keyword is
given
|
| VARCHAR |
A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification) |
The range of Length is 1 to 255 characters. VARCHAR values are sorted and compared in case-insensitive fashion unless the BINARY keyword is given |
| TINYBLOB, TINYTEXT |
A BLOB or TEXT column with a maximum length of 255 (2^8 – 1) characters |
|
| BLOB, TEXT |
A BLOB or TEXT column with a maximum length of 65535 (2^16 – 1) characters |
|
| MEDIUMBLOB, MEDIUMTEXT |
A BLOB or TEXT column with a maximum length of 16777215 (2^24 – 1) characters |
|
| LONGBLOB, LONGTEXT |
A BLOB or TEXT column with a maximum length of 4294967295 (2^32 – 1) characters |
|
| ENUM |
An enumeration |
A string object that can have only one value, chosen from the list of values ‘value1’, ‘value2’, …, or NULL. An ENUM can have a maximum of 65535 distinct values. |
| SET |
A set |
A string object that can have zero or more values, each of which must be chosen from the list of values ‘value1’, ‘value2’, … A SET can have a maximum of 64 members
|
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