CriteriaQuery equivalent for conditional sum query in MySQL? - spring

Question

In MySQL, I can use the following conditional sum query to count the number of rows, grouped by specific conditions:
SELECT SUM(synced=true) AS sum_a, SUM(synced=false) AS sum_b from test_table where name = "xyz";
I am trying to translate this into an equivalent CriteriaQuery, however, am not able to do so. How would the CriteriaQuery equivalent look for this?
So far, the closest I have reached is using a multiselect function with selectCase expressions as follows:
criteriaQuery.multiselect(
criteriaBuilder.sum(
criteriaBuilder.<Number>selectCase().when(/* conditions for sum_a */), 1
).otherwise(0)
).alias("sum_a"),
criteriaBuilder.sum(
criteriaBuilder.<Number>selectCase().when(/* conditions for sum_b */), 1
).otherwise(0)
).alias("sum_b"),
The above approach, however, is different from the SQL query mentioned at the beginning, even though it returns the correct values.

Answer 1

The query you posted looks correct. That's as good as it gets. You can't reproduce the exact same SQL with HQL or the JPA Criteria API. In fact, the syntax of the SQL query is MySQL specific and only works because MySQL doesn't have native boolean support, but models this as integer 1 and 0. The SQL standard way to model this is to use the fact that aggregate functions are null rejecting and use a case when expression that produces null if your condition is not fulfilled.
criteriaQuery.multiselect(
criteriaBuilder.sum(
criteriaBuilder.<Integer>selectCase().when(/* conditions for sum_a */), 1
).otherwise(criteriaBuilder.nullLiteral(Integer.class))
).alias("sum_a"),
criteriaBuilder.sum(
criteriaBuilder.<Integer>selectCase().when(/* conditions for sum_b */), 1
).otherwise(criteriaBuilder.nullLiteral(Integer.class))
).alias("sum_b"),