What's the difference between VARCHAR and CHAR?
2009年12月11日 · CHAR is a fixed length field; VARCHAR is a variable length field. If you are storing strings with a wildly variable length such as names, then use a VARCHAR, if the length is always the same, then use a CHAR because it is slightly more size-efficient, and also slightly faster. edited Dec 11, 2009 at 3:41.
What is the difference between char, nchar, varchar, and nvarchar …
2008年10月6日 · n [var]char stores unicode while [var]char just stores single-byte characters. [n]char requires a fixed number of characters of the exact length while [n]varchar accepts a variable number of characters up to and including the defined length. Another difference is length. Both nchar and nvarchar can be up to 4,000 characters long.
What does the specified number mean in a VARCHAR() clause?
With CHAR, column values are padded with spaces to fill the size you specified, whereas with VARCHAR, only the actual value you specified is stored. For example: CREATE TABLE test (. char_value CHAR(10), varchar_value VARCHAR(10) ); INSERT INTO test VALUES ('a', 'b'); SELECT * FROM test; The above will select "a " for char_value and "b" for ...
What is the difference between varchar and nvarchar?
2008年9月27日 · The main difference between Varchar(n) and nvarchar(n) is: Varchar ( Variable-length, non-Unicode character data) size is upto 8000. It is a variable length data type. Used to store non-Unicode characters. Occupies 1 byte of space for each character. Nvarchar: Variable-length Unicode character data.
sql - What does varchar (-1) mean? - Stack Overflow
2009年11月11日 · The documentation says: varchar [ ( n | max ) ] Variable-length, non-Unicode character data. n can be a value from 1 through 8,000. max indicates that the maximum storage size is 2^31-1 bytes. So -1 isn't technically valid. It might work, but I wouldn't use it if I were you. answered Nov 11, 2009 at 4:57.
What is the difference between varchar and varchar2 in Oracle?
2009年7月23日 · 47. Taken from the latest stable Oracle production version 12.2: Data Types. The major difference is that VARCHAR2 is an internal data type and VARCHAR is an external data type. So we need to understand the difference between an internal and external data type... Inside a database, values are stored in columns in tables.
MySQL: Why use VARCHAR(20) instead of VARCHAR(255)?
2009年8月12日 · 2. There is a semantical difference (and I believe that's the only difference): if you try to fill 30 non-space characters into varchar (20), it will produce an error, whereas it will succeed for varchar (255). So it is primarily an additional constraint. answered Aug 11, 2009 at …
MySQL VARCHAR size? - Stack Overflow
2015年1月2日 · 431k 83 597 684. 66. To be clear: Storing a string 100 characters in a varchar(200) field will take 101 bytes. Storing a string of 100 characters in a varchar(256) field will take 102 bytes. This is why you see varchar(255) so frequently; 255 characters is the longest string you can store in MySQL's varchar type with only one byte of overhead.
sql - How to convert DateTime to VarChar - Stack Overflow
2008年9月16日 · Essentially, there are 2 bytes of overhead involved in VARCHAR vs CHAR. In this scenario, we know that your string will always be 10 characters, so CHAR is appropriate. – Will Ediger
Best practices for SQL varchar column length - Stack Overflow
There's one possible performance impact: in MySQL, temporary tables and MEMORY tables store a VARCHAR column as a fixed-length column, padded out to its maximum length. If you design VARCHAR columns much larger than the greatest size you need, you will consume more memory than you have to. This affects cache efficiency, sorting speed, etc.