Use the SQL SELECT count distinct query statement to count the total number of unique values of a field in the database

If you want to count the total number of unique value contents that are not repeated in one or several fields in the database , For example, from the database “ Customer information ” Li statistics “ Address table ” Inside “ City ” How many cities are there in the field , You can use the following statement ：

SELECT COUNT(DISTINCT  City ) FROM  Customer information . Address table 

there COUNT Indicates the total number of rows of statistical query results , and DISTINCT Represents a statistically unique value , That is to say, remove the duplicate values in the query results , This query statement returns a number .

This statement can be followed by WHERE Perform conditional filtration , for instance ：

SELECT COUNT(DISTINCT  City ) FROM  Customer information . Address table  WHERE  Province =' guangdong '