difference between rack server and tower server

In a recent interview, the interviewer asked the difference between varchar and nvarchar, remembering the difference between fixed length and variable lengths, but failed to speak. Later, on the Internet to find the next user summary of the difference. Make a memo here:One, the difference between Char,varchar,nchar,nva

-------------------------------------------------------- Desserts, candies, and sweet breads Breads, crackers, pasta, and cereal This is an example of using another additional wildcard character to find some records. This example is how to select the result of the query above, the second letter of the Description field is not a record of "E". Select Description from Northwind.dbo.Categories where Patindex ("%[b,b]read%", description) > 0 and Patindex ("_[^e]%", description) = 1 By adding a p

not allowed to have empty content. The Oracle table structure is defined by not NULL for MySQL, and errors are generated when the data is being directed. As a result, null characters are judged on the data, and if NULL or NULL, it is necessary to change it to a space string.Fuzzy Comparison of stringsMySQL uses the field name like% ' String% ', Oracle can also use the field name like% ' String% ' but this method can not use the index, the speed is not fast, with a string comparison function InS

Mysql:Char defines stored characters, the actual storage is also stored as characters, size char (255 characters), note is not byte.What is the difference between a character and a byte?A byte is a unit of information stored in a computer, a byte is eight bits, a character is a, B, C, and some symbols, usually in a computer with a byte, that is, generally accounted for a byte, but there is not generally, according to the specific encoding each charact

), Managed in a constrained form. But at the same time, it automatically creates a unique nonclustered index, with the performance and some functionality of the index. In fact, unique key constraints are constrained by unique indexes. A unique index is an index that uniquely checks a field and can set various parameters for flexibility. So when we create the uniqueness of a column, which is better to use? (Personal understanding) Unique key constraints are bound to exist in a table, and the in

. 1. Causes the transaction log to not log table variables. Therefore, they are out of the scope of the transaction mechanism. 2. Any stored procedure that uses a temporary table is not precompiled, but the execution plan of the stored procedure that uses the table variable can be pre-statically compiled. The main benefit of precompiling a script is that it speeds up execution. This benefit is more significant for long stored procedures because the cost of recompiling is too high for

Tags: typeid now () time use where Server pen table name notationQuery the first 100 data #mysql Select * from - ; #sqlserver Selecttop* from table_name; From the database. Table Positioning table #mysql写法: library name. Table name Select from where userName='boss' #Sqlserver写法: library name. dbo. Table name; or: library name. Table name (note: Use two points in the middle )Selectfromwhere userName=' Boss' Get time MySQL notation: now () S

Posted from http://www.sqlservergeeks.com/primary-key-and-unique-key-difference-in-sql-server/Primary and Unique Key both enforce uniqueness of columns on which they is defined. Then where does they differ? They differ in following-A primary key doesn ' t allow null value wherein A Unique key allows one null value.-A primary keys purpose is to uniquely define a row in A table wherein unique keys purpose are

a varchar high.(4) Why use nvarchar?with n prefixes, n denotes Unicode characters, that is, all characters account for two bytes, Nchar,nvarcharCharacter, the English characters only need one byte storage is sufficient, but the Chinese character is numerous, requires two bytes of storage, English and Chinese characters are prone to confusion, the Unicode character set is to solve the problem of incompatible character sets, all of its characters are represented by two bytes, That is, the English

that the length of the corresponding length, and the variable length character data will not be filled with spaces, the exception is that the text storage is also variable length. (6) How do I use these types? If you are sure of the length of the stored data and do not pack in Chinese, you can choose the char type. If you are sure of the stored data length, but may include Chinese, you can choose the nchar type. If you are unsure of the length of the

the efficiency of a varchar high. (4) Why use nvarchar? with n prefixes, n denotes Unicode characters, that is, all characters account for two bytes, Nchar,nvarchar Character, the English characters only need one byte storage is sufficient, but the Chinese character is numerous, requires two bytes of storage, English and Chinese characters are prone to confusion, the Unicode character set is to solve the problem of incompatible character sets, all of its characters are represented by two bytes,

The difference between coercion cast and convert in SQL Server In SQL Server, both the cast and CONVERT functions are available for type conversions, and their functions are the same. Just different grammar. Cast is generally easier to use, and the advantage of convert is that you can format dates and values. Select CAST (' 123 ' as int)-- 123 Select CON

With an inner join, the condition has the same result in either the join clause or the WHERE clause, but not when an outer join is used. When the condition is in the JOIN clause, SQL Server includes all rows for the appearance, and then uses the condition to include rows from the second table. When the constraint is placed in the WHERE clause, the join is performed and the WHERE clause is applied to the join row. The above statement

In SQL Server, both the cast and CONVERT functions are available for type conversions, and their functions are the same.It's just a different syntax.Cast is generally easier to use, and the advantage of convert is that dates and values can be formatted.1 Select CAST('123' as int)--1232 Select CONVERT(int,'123')--1233 4 Select CAST(123.4 as int)--1235 Select CONVERT(int,123.4)--1236 7 Select CAST('123.4' as int)8 Select CONVERT(int,'123.4')9 --Conve