SQL: Visual QuickStart Guide

Eliminating Duplicate Rows with DISTINCT

Columns often contain duplicate values, and it’s common to want a result that lists each duplicate only once. If I type Listing 4.6 to list the states where the authors live, the result, Figure 4.6, contains unneeded duplicates. The DISTINCT keyword eliminates duplicate rows from a result.

Listing 4.6. List the states in which the authors live. See Figure 4.6 for the result.

SELECT state FROM authors;

Figure 4.6. Result of Listing 4.6. This result contains unneeded duplicates of CA and NY.

state ----- NY CO CA CA NY CA FL

To eliminate duplicate rows:

• Type:

  SELECT DISTINCT columns
    FROM table;
  

  columns is one or more comma-separated column names, and table is the name of the table that contains ...