Selection Lists

Selection Lists

When you use a SELECT statement to retrieve data, you specify a list of columns (a selection list) to include in the result table. To retrieve all the columns in a table or tables, you can use an asterisk (*) instead of a list of columns.

Note: Avoid using * in place of the list. Using * can expose an application to potential problems if the number of columns or column sizes in a table changes. Also, it typically returns unnecessary data.

The following example selects three columns from the Class table.

SELECT Name, Section, Max_Size
FROM Class;

The following example selects all columns from the Class table.

SELECT * FROM Class;

When retrieving data, Pervasive PSQL displays column names based on how you specify the names in the query.

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If you explicitly specify a column name, Pervasive PSQL returns it as you entered it. The following example specifies column names in all lowercase.

SELECT name, section, max_size FROM Class#

Pervasive PSQL returns the column names as follows:

"Name", "Section", "Max_Size"

These column names are headings for the returned data; they are not data themselves.

The following example defines aliases for the tables Department and Faculty.

SELECT d.Name, f.ID FROM Department d, Faculty f;

Pervasive PSQL returns the column names as follows:

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If you use * to specify column names, they appear in all uppercase, as in the following example.

SELECT * FROM Department;

Pervasive PSQL returns the column names as follows:

"Name", "Phone_Number", "Building_Name", "Room_Number", "Head_Of_Dept"

The following example defines aliases for the tables Department and Faculty.

SELECT * FROM Department d, Faculty f;

Pervasive PSQL returns the column names as follows:

"Building_Name"

"Building_Name"

"Rsch_Grant_Amount"