SQL数据库外文翻译解读.doc

Working with Databases This chapter describes how to use SQL statements in embedded applications to control databases. There are three database statements that set up and open databases for access: SET DATABASE declares a database handle, associates the handle with an actual database file, and optionally assigns operational parameters for the database. SET NAMES optionally specifies the character set a client application uses for CHAR, VARCHAR, and text Blob data. The server uses this information to transliterate from a database’s default character set to the client’s character set on SELECT operations, and to transliterate from a client application’s character set to the database character set on INSERT and UPDATE operations. g CONNECT opens a database, allocates system resources for it, and optionally assigns operational parameters for the database.All databases must be closed before a program ends. A database can be closed by using DISCONNECT, or by appending the RELEASE option to the final COMMIT or ROLLBACK in a program. Declaring a database Before a database can be opened and used in a program, it must first be declared with SET DATABASE to: CHAPTER 3 WORKING WITH DATABASES. Establish a database handle. Associate the database handle with a database file stored on a local or remote node.A database handle is a unique, abbreviated alias for an actual database name. Database handles are used in subsequent CONNECT, COMMIT RELEASE, and ROLLBACK RELEASE statements to specify which databases they should affect. Except in dynamic SQL (DSQL) applications, database handles can also be used inside transaction blocks to qualify, or differentiate, table names when two or more open databases contain identically named tables. Each database handle must be unique among all variables used in a program. Database handles cannot duplicate host-language reserved words, and cannot be InterBase reserved words.The following statement illustrates a simple database declaration: EXEC SQL