Database systems Lecture 2 – Data Types Roman Danel 2016

Data types Numeric String Date and Time Others (binary, spatial, XML…)

Numeric data types Integer Real (with decimal point) Decimal, Numeric Float - floating point

Numeric in MySQL (Integer) Tinyint −128 až 127 nebo 0 až 255 pro UNSIGNED, 1 byte Smallint −32768 to 32767 or 0 to 65535 for UNSIGNED, 2 bytes MediumInt −8388608 to 8388607 or 0 to 16777215 for UNSIGNED, 3 bytes Int −2147483648 to2147483647 or 0 to 4294967295 for UNSIGNED, 4 bytes Bigint −9223372036854775808 to 9223372036854 or 0 to 18446744073709551615 pro UNSIGNED, 8 bytes

Numeric Data Types in MySQL Float(p) Float(M,D) Double(M,D) Decimal(M,D) - large numbers in floating point stored as a string (1 byte per numeral)

Numeric – Microsoft SQL Server Data Type Range Memmory Allocation bigint -263 až 263 8 bytes int -231 až 231 4 bytes smallint -215 až 215 2 bytes tinyint 0 až 255 1 byte Data Type Precision Memmory Allocation decimal 1-9 5 bytes 10-19 9 bytes 20-28 13 bytes 29-38 17 bytes

Numeric – Microsoft SQL Server Data type Range Memory Allocation money -922,337,203,6­85,477.58 to 922,337,203,6­85,477.58 8 bytes smallmoney - 214,748.3648 to 214,748.3647 4 bytes

Numeric – Microsoft SQL Server Data type Range Memory Allocation float(n) 1-24 4 bajty 25-53 9 bajtů

Numeric Numeric(5,2) = 99.99

String Data Types - MySQL Char(m), m=0-255, longer will be „lost“ Varchar(m), m=0-255 Tinyblob - 0 to 255 Bytes Blob - 0 to 65535 Bytes Mediumblob, Longblob TinyText -  0 až 255 bajtů Text, MediumText, LongText Enum - enumeration values; the values in the column can be assigned just one value from a list of values

Date Data Types DATE TIME DATETIME SMALLDATETIME

Date – Microsoft SQL Server Data type Range Memory Allocation date 0001-01-01 to 9999-12-31 3 bytes Time 00:00:00.000 to 23:59:59.999 5 bytes Datetime Rozsah pro datum 01.01.1753 až 31.12.9999 Rozsah pro čas 00:00:00 až 23:59:59.997 8 bytes Datetime2(n) Range for Date 01.01.0001 to 31.12.9999 Range for time 00:00:00 to 23:59:59.9999999 According precission from 6 to 8 bytes Datetimeoffset Range for Date 01.01.0001 to 31.12.9999 Range for time00:00:00 to 23:59:59.9999999 Time zone-14:00 až +14:00 10 bytes Smalldatetime Range for Date 01.01.1900 to 06.06.2079 Range for time 00:00:00 to 23:59:00 4 bytes

Others Data Types – MS SQL Bit – 1/0, memmory allocation - 1 bit Timestamp – It is a data type that generates unique binary number, which is used for version resolution lines "rowversion". This data type does not store date and time! To store the date and time should be used datetime2. In memory occupies 8 bytes. Uniqueidentifier – It is a data type that, for example, in conjunction with the function NEWID () generates a unique identifier. In memory it takes up 16 bytes.

Value NULL Value, which is not intended Property of the column: NULL/NOT NULL Example in SELECT: SELECT * from table where column_name IS NULL;

Primary Key Primary Key – defined over one or more columns of the table. The main purpose of a primary key is ensure the uniqueness of records in a table. Primary key values can not contain duplicate or null.

Automatically generated number MySQL – AUTO_INCREMENT MS SQL – IDENTITY Oracle – sequence Access – Automatic Number create table Table_name ( column_name int IDENTITY(1,1) primary key,

Default Value Apply if during operation insert the value is not determined If we want to avoid NULL values

Column Properties UNIQUE NULL/NOT NULL PRIMARY KEY DEFAULT

Converting Data Types CONVERT CAST CAST ( $157.27 AS VARCHAR(10) ) Syntax for CAST: CAST ( expression AS data_type [ (length ) ]) Syntax for CONVERT: CONVERT ( data_type [ ( length ) ] , expression [ , style ] )