Creating Tables
When you create a table, you must name it. Each table name must be unique within a database. For more information about rules for naming tables, refer to the section Naming Conventions.
When you are deciding which tables to create in your database, consider that different users can look at data in different combinations using views. A view looks like a table and can be treated as a table for most purposes (such as retrieving, updating, and deleting data). However, a view is not necessarily associated with a single table; it can combine information from multiple tables. For more information, refer to Retrieving Data.
You can create a table using Pervasive PSQL Control Center. See To start Table Editor for a new table in Pervasive PSQL User's Guide.
Aliases
You can assign aliases (also called alias names) to table names in the following elements of statements:
•
FROM clause of a SELECT or DELETE statement.
•
INTO clause of an INSERT statement.
•
List of tables in an UPDATE statement.
*Note: Aliases apply only to the statement in which you use them. Pervasive PSQL does not store them in the data dictionary.
An alias can be any combination of up to 20 characters. Always separate the table name from the alias with a blank. Separate the alias and the column name with a period (.). Once you specify an alias for a particular table, you can use it elsewhere in the statement to qualify column names from that table.
The following example specifies the alias name s for the table Student and e for the table Enrolls.
SELECT s.ID, e.Grade
FROM Student s, Enrolls e
WHERE s.ID = e.Student_ID#
You can use an alias to do the following:
•
Replace long table names.
When you are working interactively, using aliases can save typing time, especially when you need to qualify column names. For example, the following statement assigns s as the alias for the Student table, e for the Enrolls table, and c1 for the Class table. This example uses aliases to distinguish the source of each column in the selection list and in the WHERE conditions.
SELECT s.ID, e.Grade, c1.ID
FROM Student s, Enrolls e, Class c1
WHERE (s.ID = e.Student_ID) AND
(e.Class_ID = c1.ID)#
•
Make a statement more readable. Even in statements with only a single table name, an alias can make the statement easier to read.
•
Use the table in the outer query in a correlated subquery:
SELECT s.ID, e.Grade, c1.ID
FROM Student s, Enrolls e, Class c1
WHERE (s.ID = e.Student_ID) AND
(e.Class_ID = c1.ID) AND
e.Grade >=
(SELECT MAX (e2.Grade)
FROM Enrolls e2
WHERE e2.Class_ID = e.Class_ID)#