Beginning SQL, Differences Between Oracle and （Oracle和SQL,开始区别）.pdfVIP

Beginning SQL, Differences Between Oracle and Microsoft If youre new to SQL or just new to Oracle SQL, perhaps coming from a Microsoft SQL Server environment, it may seem like the two versions should be very similar, and they are, to a certain degree, ut they are also very different in some important and basic ways. You may need to know these differences because of a migration effort from one to the other, or because you need to access both of them in your day-to-day operations. Perhaps you have an Oracle server being downloaded into a SQL Server data warehouse, or perhaps you have distributed SQL Server databases being uploade into a consolidating Oracle database. For these and other circumstances under which these two exist, you may need to be aware of the differences between the two versions of the SQL language. So what are the differences from SQL Server to Oracle? Part I. A Quick Intro for the SQL Server User Dont Use Databases Well, first of all, we dont use data ases, we connect to them: SQL Server use mydatabase Oracle connect mydatabase/mypassword Use Dual And then, our select statements have different options, in this instance requiring a from clause: SQL Server select getdate(); Oracle select getdate() from dual; so we use that dummy we call DUAL. Did you notice the lack of a from clause in the first version? Its a nice shortcut, but Oracle doesnt allow it, nor does ANSI SQL92. Select Into And we dont select rows into a table, but instead, insert the rows y selecting them: SQL Server select getdate() mycolumn into mytable; Oracle insert into mytable select sysdate() mycolumn from dual; Actually, the SQL Server version creates a table if one doesn’t exist, so the Oracle version would require a CREATE TABLE AS statement to arrive at the same result. Inserts By the way, the into clause of an insert statement is not an option on Oracle; its