1. Database systems Lecture 2 – Data Types
Roman Danel
2016

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

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

4. Numeric in MySQL (Integer)
Tinyint
−128 až 127 nebo 0 až 255 pro UNSIGNED, 1 byte
Smallint
−32768 to or 0 to for UNSIGNED, 2 bytes
MediumInt
− to or 0 to for UNSIGNED, 3 bytes
Int
− to or 0 to for UNSIGNED, 4 bytes
Bigint
− to or 0 to pro UNSIGNED, 8 bytes

5. 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)

6. 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

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

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

9. Numeric
Numeric(5,2) = 99.99

10. 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

11. Date Data Types
DATE
TIME
DATETIME
SMALLDATETIME

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

13. 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.

14. 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;

15. 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.

16. 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,

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

18. Column Properties
UNIQUE
NULL/NOT NULL
PRIMARY KEY
DEFAULT

19. 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 ] )