MySQL Chapter 2Linux教学课件.ppt

RHEL Clustering Storage Management Developing With MySQL C/S --protocol tcp, socket, pipe, memory Data type 修饰 SQL database table index view SELECT, UPDATE, INSERT, DELETE SUBquery, join Agenda MySQL data types MySQL Language Structure Data Type Each data type has several characteristics: What kind of values it can represent How much space values take up Whether values are fixed-length (all values of the type take the same amount of space) or variable-length (the amount of space depends on the particular value being stored) How MySQL compares and sorts values of the type Whether the type can be indexed Data types overview In order to store, retrieve, or process data, the data must be assigned a data type MySQL includes many of the ISO SQL:2003 standard data types, and adds in more data types Character String Types Binary Large Object String Types Numeric Types Boolean Types Datetime Types Internal Types Overview of Data Types Numeric Data Types String Data Types Date and Time Data Types String Data Types The ISO SQL:2003 standard defines three character string types Each string type has more than one keyword associated with it Fixed-width strings: CHARACTER(length) CHAR(length) Variable-length strings: CHARACTER VARYING(length) CHAR VARYING(length) VARCHAR(length) MySQL specific string types MySQL also supports the following nonstandard string types: TINYTEXT TEXT MEDIUMTEXT LONGTEXT Unlike most data types, the four TEXT data type fields are objects separate from the containing table or result set They are queried as regular fields are, but behind the scenes they are not actually stored in the table, they are stored as separate objects length of string types The CHAR and VARCHAR data types require a length argument A data type of CHAR or VARCHAR with a length of 0 is valid, but can hold only two values: the empty string and NULL Character string type attributes NOT NULL —By default, NULL values are allowed. To disallow NULL values, use the NOT NULL