[Explain] Data Types in SQL Server

(1) Char, varchar, text and nchar, nvarchar, ntext
Char and varchar are both between 1 and 8000 characters in length. The difference is that char is a fixed-length character data while varchar is a variable-length character data. The so-called fixed length is a fixed length. when the length of the input data does not reach the specified length, it is automatically filled with English spaces to make the length reach the corresponding length; the variable-length character data is not filled with spaces. Text stores variable-length non-Unicode data. The maximum length is 2 ^ 31-1 (2,147,483,647) characters.
Compared with the preceding three data types, the names only contain letters "N", which indicate that the characters of the Unicode data type are stored. WrittenProgramFriends should be familiar with Unicode. It is enough to store only one byte of English characters, but there are many Chinese characters and two bytes are required for storage. It is easy to cause confusion when both English and Chinese characters exist, unicode Character Set is generated to solve the incompatibility problem of character sets. All its characters are expressed in two bytes, that is, English characters are also expressed in two bytes. The length of nchar and nvarchar is between 1 and 4000. Compared with Char and varchar, nchar and nvarchar can store up to 4000 characters, whether in English or Chinese. Char and varchar can store up to 8000 English and 4000 Chinese characters. It can be seen that when using nchar and nvarchar data types, you do not have to worry about whether the entered characters are English or Chinese characters, which is more convenient, but there is some loss in the amount of stored English hours.

(2) datetime and smalldatetime
Datetime: Date and Time data from January 1, 3% to seconds.
Smalldatetime: Date and Time data from January 1, January 1-20, 1900 to January 1, June 6, accurate to minutes.

(3) bitint, Int, smallint, tinyint, and bit
Bigint: integer data from-2 ^ 63 (-9223372036854775808) to 2 ^ 63-1 (9223372036854775807.
INT: integer data from-2 ^ 31 (-2,147,483,648) to 2 ^ 31-1 (2,147,483,647.
Smallint: integer data from-2 ^ 15 (-32,768) to 2 ^ 15-1 (32,767.
Tinyint: integer data from 0 to 255.
Bit: an integer of 1 or 0.

(4) decimal and numeric
The two data types are equivalent. There are two parameters: P (precision) and S (number of decimal places ). P specifies the maximum number of decimal digits that can be stored on the left and right of the decimal point. P must be a value ranging from 1 to 38. S specifies the maximum number of decimal digits that can be stored on the right of the decimal point. s must be a value ranging from 0 to P. The default decimal place is 0.

(5) float and real
Float: floating point data from-1.79 ^ 308 to 1.79 ^ 308.
Real: floating point data from-3.40 ^ 38 to 3.40 ^ 38. In SQL Server, the synonym for real is float (24 ).