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This chapter is from the book

This chapter is from the book

SQL in 10 Minutes a Day, Sams Teach Yourself, 5th EditionSQL in 10 Minutes a Day, Sams Teach Yourself, 5th Edition

Learn More Buy

This chapter is from the book

This chapter is from the book

SQL in 10 Minutes a Day, Sams Teach Yourself, 5th EditionSQL in 10 Minutes a Day, Sams Teach Yourself, 5th Edition

Learn More Buy

Retrieving All Columns

In addition to being able to specify desired columns (one or more, as seen above), SELECT statements can also request all columns without having to list them individually. This is done using the asterisk (*) wildcard character in lieu of actual column names, as follows:

Input ▾

SELECT *
FROM Products;

Analysis ▾

When a wildcard (*) is specified, all the columns in the table are returned. The column order will typically, but not always, be the physical order in which the columns appear in the table definition. However, SQL data is seldom displayed as is. (Usually, it is returned to an application that formats or presents the data as needed). As such, this should not pose a problem.

CAUTION: USING WILDCARDS

As a rule, you are better off not using the * wildcard unless you really do need every column in the table. Even though use of wildcards may save you the time and effort needed to list the desired columns explicitly, retrieving unnecessary columns usually slows down the performance of your retrieval and your application.

TIP: RETRIEVING UNKNOWN COLUMNS

There is one big advantage to using wildcards. As you do not explicitly specify column names (because the asterisk retrieves every column), it is possible to retrieve columns whose names are unknown.

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