How to count the number of records after MySQL grouping

After MySQL is grouped, the method of counting the number of records: 1. Count the number of records, the code is [SELECT num, count(*) AS counts from test_a GROUP BY num]; 2. After deduplication of num Quantity statistics.

MySQL method to count the number of records after grouping:

After grouping, count the number of records Number:

SELECT num,count(*) AS counts from test_a GROUP BY num;

The query results are as follows:

Statistics on the number of num after deduplication:

　　SELECT count(t.counts) FROM ( SELECT num,count(*) AS counts from test_a GROUP BY num ) AS t;
　　SELECT count(DISTINCT num) AS count FROM test_a;

The two results are the same, both are 5; except that one is a subquery (nested) and the other is the built-in function distinct();

Database structure

More related free learning recommendations: mysql tutorial(Video)

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