SQL Having
HAVING is a filter keyword that applies to the already grouped records. Unlike WHERE, which is used for conditions to filter the records, HAVING is used with a condition presented as an aggregate function and applied to the result obtained with the GROUP BY. Thus, the HAVING operator is only used with GROUP BY and only after this operator.
The syntax is next:
1234567--do not run this query SELECT col1, col2, ... FROM table WHERE conditions GROUP BY col1, col2, ... HAVING agg_conditions ORDER BY col1, col2, ...;
For example, you want to get info about singers and their songs: singers' names and the price of their most expensive song. To do that, you can use GROUP BY the singer and display the price using the function MAX(). But let it be the limit: you need only singers such that the maximum price is less than 1000. The next query solves this problem:
1234SELECT singer, MAX(price) FROM songs GROUP BY singer HAVING MAX(price) < 1000
This way, you can add a condition to the aggregate function MAX(). You cannot do that in WHERE statement, that's why we need to use HAVING.
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Retrieve info about the singers and their number of songs. Select only singers with at least 2 songs. Order records by the number of songs in groups starting with the biggest one.
Solution
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HAVING is a filter keyword that applies to the already grouped records. Unlike WHERE, which is used for conditions to filter the records, HAVING is used with a condition presented as an aggregate function and applied to the result obtained with the GROUP BY. Thus, the HAVING operator is only used with GROUP BY and only after this operator.
The syntax is next:
1234567--do not run this query SELECT col1, col2, ... FROM table WHERE conditions GROUP BY col1, col2, ... HAVING agg_conditions ORDER BY col1, col2, ...;
For example, you want to get info about singers and their songs: singers' names and the price of their most expensive song. To do that, you can use GROUP BY the singer and display the price using the function MAX(). But let it be the limit: you need only singers such that the maximum price is less than 1000. The next query solves this problem:
1234SELECT singer, MAX(price) FROM songs GROUP BY singer HAVING MAX(price) < 1000
This way, you can add a condition to the aggregate function MAX(). You cannot do that in WHERE statement, that's why we need to use HAVING.
Swipe to start coding
Retrieve info about the singers and their number of songs. Select only singers with at least 2 songs. Order records by the number of songs in groups starting with the biggest one.
Solution
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Awesome!
Completion rate improved to 4.17single
