Databases Reference
In-Depth Information
APPENDIX
B
You can use this appendix to obtain details concerning important components and syntax for SQL. Items are
arranged alphabetically. Each item contains a description and, where appropriate, both an example and a
description of the query results. Some SQL commands also include a description of the clauses associated with
them. For each clause, there is a brief description and an indication of whether the clause is required or optional.
Use the ALTER TABLE command to change a table's structure. As shown in Figure B-1, you type the ALTER
TABLE command, followed by the table name, and then the alteration to perform. (
Note:
In Access, you usu-
ally make these changes to a table in Design view rather than using ALTER TABLE.)
Clause
Description
Required?
ALTER TABLE
table name
Indicates the name of table to be altered.
Yes
alteration
Indicates the type of alteration to be performed.
Yes
FIGURE B-1
ALTER TABLE command
The following command alters the Customer table by adding a new column named CustType:
ALTER TABLE Customer
ADD CustType CHAR(1)
;
The following command alters the Customer table by changing the length of the CustomerName column:
ALTER TABLE Customer
CHANGE COLUMN CustomerName TO CHAR(50)
;
The following command alters the Part table by deleting the Warehouse column:
ALTER TABLE Part
DELETE Warehouse
;
To select columns, use a SELECT clause with the list of columns separated by commas. The following SELECT
clause selects the CustomerNum, CustomerName, and Balance columns:
SELECT CustomerNum, CustomerName, Balance
Use an asterisk in a SELECT clause to select all columns in the table. The following SELECT command
selects all columns in the Part table:
SELECT *
FROM Part
;
You can use a computation in place of a field by typing the computation. For readability, you can type the
computation in parentheses, although it is not necessary to do so.
