SQL veri tipi demek ne tür verileri depolanacağıyla belirlenmesinde kullanılır. Yani bir sayı mı tutacaksınız yoksa bir metin mi yoksa, resim, tarih vs…
Bu yazımızda database’ de bir tablo oluştururken veri tülerinin ne olması gerektiğini öğreneceğiz. Tablolarınızdaki her bir sutun(kolon) sizde bir veri tipi isteyecektir. Bunları belirlemeden tablonuzu oluşturamazsınız. Bu yüzden tablo oluşturmadan önce veri tiplerimize karar vermemiz çok önemlidir. En uygun şekilde kolonların veri tiplerini belirlemek database’ inizin ne kadar yer kaplayacağını ve performansını etkileyecektir.
SQL Veri Tipleri
Şimdi gelelim veri türlerimize ve ne işe yaradıklarına. SQL’ de 4 ana başlıkta veri tipleri mevcuttur.
1. Metinsel SQL Veri Tipi (String data types)
| Data type | Description | Max size | Storage |
|---|---|---|---|
| char(n) | Fixed width character string | 8,000 characters | Defined width |
| varchar(n) | Variable width character string | 8,000 characters | 2 bytes + number of chars |
| varchar(max) | Variable width character string | 1,073,741,824 characters | 2 bytes + number of chars |
| text | Variable width character string | 2GB of text data | 4 bytes + number of chars |
| nchar | Fixed width Unicode string | 4,000 characters | Defined width x 2 |
| nvarchar | Variable width Unicode string | 4,000 characters | |
| nvarchar(max) | Variable width Unicode string | 536,870,912 characters | |
| ntext | Variable width Unicode string | 2GB of text data | |
| binary(n) | Fixed width binary string | 8,000 bytes | |
| varbinary | Variable width binary string | 8,000 bytes | |
| varbinary(max) | Variable width binary string | 2GB | |
| image | Variable width binary string | 2GB |
2. Nümerik SQL Veri Tipi (Number data types)
| Data type | Description | Storage |
|---|---|---|
| bit | Integer that can be 0, 1, or NULL | |
| tinyint | Allows whole numbers from 0 to 255 | 1 byte |
| smallint | Allows whole numbers between -32,768 and 32,767 | 2 bytes |
| int | Allows whole numbers between -2,147,483,648 and 2,147,483,647 | 4 bytes |
| bigint | Allows whole numbers between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807 | 8 bytes |
| decimal(p,s) | Fixed precision and scale numbers.Allows numbers from -10^38 +1 to 10^38 –1. The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18. The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0 | 5-17 bytes |
| numeric(p,s) | Fixed precision and scale numbers.Allows numbers from -10^38 +1 to 10^38 –1. The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18. The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0 | 5-17 bytes |
| smallmoney | Monetary data from -214,748.3648 to 214,748.3647 | 4 bytes |
| money | Monetary data from -922,337,203,685,477.5808 to 922,337,203,685,477.5807 | 8 bytes |
| float(n) | Floating precision number data from -1.79E + 308 to 1.79E + 308.The n parameter indicates whether the field should hold 4 or 8 bytes. float(24) holds a 4-byte field and float(53) holds an 8-byte field. Default value of n is 53. | 4 or 8 bytes |
| real | Floating precision number data from -3.40E + 38 to 3.40E + 38 | 4 bytes |
3. Tarihsel Veri Tipleri (Date data types)
| Data type | Description | Storage |
|---|---|---|
| datetime | From January 1, 1753 to December 31, 9999 with an accuracy of 3.33 milliseconds | 8 bytes |
| datetime2 | From January 1, 0001 to December 31, 9999 with an accuracy of 100 nanoseconds | 6-8 bytes |
| smalldatetime | From January 1, 1900 to June 6, 2079 with an accuracy of 1 minute | 4 bytes |
| date | Store a date only. From January 1, 0001 to December 31, 9999 | 3 bytes |
| time | Store a time only to an accuracy of 100 nanoseconds | 3-5 bytes |
| datetimeoffset | The same as datetime2 with the addition of a time zone offset | 8-10 bytes |
| timestamp | Stores a unique number that gets updated every time a row gets created or modified. The timestamp value is based upon an internal clock and does not correspond to real time. Each table may have only one timestamp variable |
4. Diğer SQL Veri Tipi (Other data types)
| Data type | Description |
|---|---|
| sql_variant | Stores up to 8,000 bytes of data of various data types, except text, ntext, and timestamp |
| uniqueidentifier | Stores a globally unique identifier (GUID) |
| xml | Stores XML formatted data. Maximum 2GB |
| cursor | Stores a reference to a cursor used for database operations |
| table | Stores a result-set for later processing |
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