sql tutorial

SQL Server backup and disaster recovery The data processing becomes more and more important in the modern enterprise operation, more and more crucial, may even become the enterprise development bottleneck. The importance of data protection is

Access to | data | Database Access database (3) Hello everybody, I am Wuhan Hua Division's Sunwen. The previous lesson tells you how to open a database and do some of the most basic things about the Db2.mdb database. Everyone must feel that the

To select data from two or more tables, we typically use table joins to implement this functionality. This section describes the concept of join (join). For this we prepared two test tables: album (album table) and track (track table). Album table:

Tutorials | view Q: Why is SQL Server not allowed to use an ORDER BY clause in the view definition? A: SQL Server does not allow the ORDER BY clause to be used in the view definition to comply with the ANSI SQL-92 standard. Because the principle

So far, we've been connected to two different tables, so can we connect ourselves to a single table? The answer is yes. Is it necessary to make a self connection to a table? The answer is yes. Alias for table: A table can be connected to itself.

Before introducing the group BY and having clauses, we must first talk about a special function in the SQL language: aggregate functions, such as SUM, COUNT, MAX, AVG, and so on. The fundamental difference between these functions and other functions

Before introducing the group BY and having clauses, we must first talk about a special function in the SQL language: aggregate functions, such as SUM, COUNT, MAX, AVG, and so on. The fundamental difference between these functions and other functions

Several suggestions for improving SQL execution efficiency: Try not to include subqueries in the Where; About the time of the query, try not to write: where To_char (dif_date, ' Yyyy-mm-dd ') =to_char (' 2007-07-01 ', ' yyyy-mm-dd '); In the

A nested SELECT statement is also called a subquery, in the form of: Select name from BBC where region = (select Region from BBC where name = ' Brazil ') The query result of a SELECT statement can be the input value of another statement. The