MySql

MySQL at a Glance

Prepared by: Sahil Goel

Features of MySql

• Written in C and C++.• Works on many different platforms.• Designed to be fully multi-threaded using kernel

threads, to easily use multiple CPUs if they are available.• A privilege and password system that is very flexible and

secure.• Support for large databases. e.g.: dev.mysql.com use

MySQL Server with databases that contain 50 million records. Some users use MySQL Server with 200,000 tables and about 5,000,000,000 rows.

• Support for upto 64 indexes per table.

Data TypesProperly defining the fields in a table is important to the overall optimization of our database. We should use only the type and size of field we really need to use; don't define a field as 10 characters wide if we know we're only going to use 2 characters.

MySQL uses many different data types, broken into three categories: -numeric, -date and time, and

- string types.

Numeric Data Types:• INT - A normal-sized integer that can be signed or unsigned. If signed, the

allowable range is from -214,74,83,648 to 214,74,83,647. If unsigned, the allowable range is from 0 to 429,49,67,295.

• TINYINT - A very small integer that can be signed or unsigned. If signed, the allowable range is from -128 to 127. If unsigned, the allowable range is from 0 to 255.

• SMALLINT - A small integer that can be signed or unsigned. If signed, the allowable range is from -32,768 to 32,767. If unsigned, the allowable range is from 0 to 65,535.

• MEDIUMINT - A medium-sized integer that can be signed or unsigned. If signed, the allowable range is from -83,88,608 to 83,88,607. If unsigned, the allowable range is from 0 to 16777215.

• BIGINT - A large integer that can be signed or unsigned. If signed, the allowable range is from -9223372036854775808 to 9223372036854775807. If unsigned, the allowable range is from 0 to 18446744073709551615.

Numeric Data Types(Cont.):

• FLOAT(M,D) - A floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 10,2, where 2 is the number of decimals and 10 is the total number of digits (including decimals). Decimal precision can go to 24 places for a FLOAT.

• DOUBLE(M,D) - A double precision floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 16,4, where 4 is the number of decimals. Decimal precision can go to 53 places for a DOUBLE. REAL is a synonym for DOUBLE.

• DECIMAL(M,D) - Values for DECIMAL columns in MySQL 5.6 are stored using a binary format that packs nine decimal digits into 4 bytes and any remaining digits left over require some fraction of 4 bytes.

Date and Time Types:• DATE - A date in YYYY-MM-DD format, between 1000-01-01 and 9999-12-31. For example,

December 30th, 1973 would be stored as 1973-12-30.• DATETIME - A date and time combination in YYYY-MM-DD HH:MM:SS format,

between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. For example, 3:30 in the afternoon on December 30th, 1973 would be stored as 1973-12-30 15:30:00.

• TIMESTAMP - A timestamp between midnight, January 1, 1970 and sometime in 2037. This looks like the previous DATETIME format, only without the hyphens between numbers; 3:30 in the afternoon on December 30th, 1973 would be stored as 19731230153000 ( YYYYMMDDHHMMSS ).

• TIME - Stores the time in HH:MM:SS format.• YEAR(M) - Stores a year in 2-digit or 4-digit format. If the length is

specified as 2 (for example YEAR(2)), YEAR can be 1970 to 2069 (70 to 69). If the length is specified as 4, YEAR can be 1901 to 2155. The default length is 4

String Types• CHAR(M) - A fixed-length string between 1 and 255 characters in

length (for example CHAR(5)), right-padded with spaces to the specified length when stored. Defining a length is not required, but the default is 1.

• VARCHAR(M) - A variable-length string between 1 and 65535 characters in length; for example VARCHAR(25). You must define a length when creating a VARCHAR field.

• BLOB or TEXT - A field with a maximum length of 65535 characters. BLOBs are "Binary Large Objects" and are used to store large amounts of binary data, such as images or other types of files. Fields defined as TEXT also hold large amounts of data; the difference between the two is that sorts and comparisons on stored data are case sensitive on BLOBs and are not case sensitive in TEXT fields. You do not specify a length with BLOB or TEXT.

String Types(Cont.):• TINYBLOB or TINYTEXT - A BLOB or TEXT column with a maximum

length of 255 characters. You do not specify a length with TINYBLOB or TINYTEXT.

• MEDIUMBLOB or MEDIUMTEXT - A BLOB or TEXT column with a maximum length of 167,77,215 characters. You do not specify a length with MEDIUMBLOB or MEDIUMTEXT.

• LONGBLOB or LONGTEXT - A BLOB or TEXT column with a maximum length of 429,49,67,295 characters. You do not specify a length with LONGBLOB or LONGTEXT.

• ENUM - An enumeration, which is a fancy term for list. When defining an ENUM, you are creating a list of items from which the value must be selected (or it can be NULL). For example, if you wanted your field to contain "A" or "B" or "C", you would define your ENUM as ENUM ('A', 'B', 'C') and only those values (or NULL) could ever populate that field.

Storage Engine• A storage engine is a software

module that a database management system uses to create, read, update data from a database. There are two types of storage engines in MySQL. Transactional and non-transactional.

• The default storage engine for MySQL prior to version 5.5 was MyISAM. For MySQL 5.5 and later, the default storage engine is InnoDB. Choosing the right storage engine is an important strategic decision.

List of storage engines

– MyISAM– InnoDB– Memory– CSV– Merge– Archive– Blackhole

Storage Engines• MyISAM is the original storage engine. It is a fast storage engine. It does

not support transactions. MyISAM provides table-level locking. It is used most in Web, data warehousing.

• InnoDB is the most widely used storage engine with transaction support. It is an ACID compliant storage engine. It supports row-level locking, crash recovery and multi-version concurrency control

• Memory storage engine creates tables in memory. It is the fastest engine. It provides table-level locking. It does not support transactions. Memory storage engine is ideal for creating temporary tables or quick lookups. The data is lost when the database is restarted.

• CSV stores data in csv files. It provides great flexibility, because data in this format is easily integrated into other applications.

Storage Engines(Cont.):• Merge operates on underlying MyISAM tables. Merge tables help

manage large volumes of data more easily. It logically groups a series of identical MyISAM tables, and references them as one object. Good for data warehousing environments.

• Archive storage engine is optimized for high speed inserting. It compresses data as it is inserted. It does not support transactions. It is ideal for storing, retrieving large amounts of seldom referenced historical, archived data.

• The Blackhole storage engine accepts but does not store data. Retrievals always return an empty set. The functionality can be used in distributed database design where data is automatically replicated, but not stored locally. This storage engine can be used to perform performance tests or other testing.

MySQL functions

MySQL built-in functions can be categorized into several groups: • Mathematical functions• Aggregate functions• String functions• Date and time functions• System Functions

Mathematical functions

Mathematical functions(Cont.)

Mathematical functions(Cont.)

Aggregate functions

• We have the Cars table.

Aggregate functions(Cont.)

String functions

String functions(Cont.)

String functions(Cont.)

Date & time functions

Date & time functions(Cont.)

Date & time functions(Cont.)

Date & time functions(Cont.)

System Functions

MySQL Charset/Collate• A "character" is composed of one or more bytes, and represents what

we think of when reading.

• A byte can represent only 256 different values. There are over 11,000 Korean characters and over 40,000 Chinese characters -- no way to squeeze such a character into a single byte.

• Charset vs. collation. These are different things! 'Charset' refers to the bits used to represent 'characters'. 'Collation' refers to how those bits could be compare for inequality (WHERE) and sorting (ORDER BY). GROUP BY and FOREIGN KEY CONSTRAINTS can also involve collation. And it even can involve deciding whether two different bit strings compare 'equal'.

• We can specify character sets at the server, database, table, and column level.

Collations have these general characteristics

• Two different character sets cannot have the same collation.

• Each character set has one collation that is the default collation.

• There is a convention for collation names: They start with the name of the character set with which they are associated, they usually include a language name, and they end with _ci (case insensitive), _cs (case sensitive), or _bin (binary).

Few Design Tips

• If we choose our Numeric Data Type as:– INT(1)– BIGINT AUTO_INCREMENT– No UNSIGNED used– DECIMAL(31,0)

Few Design Tips(Cont.)• Choosing our Numeric Data Type

❖ INT(1) - 1 does not mean 1 digit ❖ (1) represents client output display format only ❖ INT is 4 Bytes, TINYINT is 1 Byte ❖ TINYINT UNSIGNED can store from 0 – 255 ❖ BIT is even better when values are 0 - 1

• BIGINT is not needed for AUTO_INCREMENT ❖ INT UNSIGNED stores 4.3 billion values

• Best Practice- ❖ All integer columns UNSIGNED unless there is a reason otherwise

• Using Codes or ENUM- ❖ e.g. 'M', 'F' instead of 'Male', 'Female‘ ❖ e.g. 'A', 'I' instead of 'Active', 'Inactive‘

• NOT NULL- ❖ Saves up to a byte per column per row of data ❖ Double benefit for indexed columns

Few Design Tips(Cont.)• Know about character sets

❖ Can be defined at database, schema, table or column level ❖(if using UTF8) Only define columns that need UTF8

❖ e.g. Codes, MD5 Value, web address ❖ e.g. VARCHAR(255) utf8 is 765 bytes to store just 1 byte

• Using SELECT * ❖ MySQL Internal Temporary table will force Temp Disk Table

• Know Every SQL Statement ❖ Developers don't write proper SQL statements ❖ SQL statements will directly affect our performance

For Example : ❖ Repeating SQL statements for no benefit ❖ 1000 very quick small unnecessary queries is worse then 1 slow query

Few Design Tips(Cont.)• Naming Standards

❖ Name all Primary Keyʼs Uniquely e.g. customer_id, order_id not id

❖ Be Descriptive e.g. invoice_date not just date

❖ Avoid Reserved Words e.g. date, time

Thank You