Conversion: differences between char, varchar, text, nchar, nvarchar, and ntext in SQL Server

Conversion: differences between char, varchar, text, nchar, nvarchar, and ntext in SQL Server

Many developers often do not consider the char and varchar types when designing databases. Some developers do not pay attention to them because the storage price is getting cheaper and cheaper, I forgot some of the basic design theories and principles at the beginning. This reminds me of the young people who have moved away from their hands with a wave of RMB. In fact, I want to be a human or a human, development is good, and the grasp of details directly determines a lot. Of course, there are still some people who just don't know their differences, so they just choose one. Here I want to make a simple analysis on them. Of course, if there is something wrong with them, I hope you can give me some advice. 1. Char. It is very convenient for Char to store fixed-length data, and the indexing efficiency of char fields is high. For example, if char (10) is defined, no matter whether the data you store reaches 10 bytes, it takes up 10 bytes of space. If the space is insufficient, it is automatically filled with spaces. Therefore, trim () may be used multiple times during reading (). 2. varchar. Variable-length data is stored, but the storage efficiency is not as high as char. If the possible value of a field is not fixed, we only know that it cannot exceed 10 characters. It is the most cost-effective to define it as varchar (10. The actual length of the varchar type is the actual length of its value plus 1. Why "+ 1? This byte is used to save the actual length. From the perspective of space, it is appropriate to use varchar; from the perspective of efficiency, char is suitable, and the key is to find a trade-off point based on the actual situation. 3. Text. Text stores variable-length non-Unicode data. The maximum length is 2 ^ 31-1 (2,147,483,647) characters. 4. nchar, nvarchar, and ntext. The three names are named N more than the first three ". It indicates that characters of the Unicode data type are stored. We know that only one byte is required for 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. Therefore, in general, if it contains Chinese characters, use nchar/nvarchar. If it contains English letters and numbers, use Char/varchar. I will summarize their differences: Char, nchar fixed length, fast speed, large space, need to be processed Varchar, nvarchar, and text cannot be long, the space is small, and the speed is slow. No processing is required. Nchar, nvarchar, and ntext process Unicode codes