在jOOQ中带有条件的MySQL sum（）

Question

MySQL will allow me to pass a condition as a parameter to SUM().

SELECT COUNT(*), SUM(value > 100) FROM TABLE1;

As seen in this answer .

How do I do this in JOOQ?

Answer 1

Currently (as of jOOQ 3.4), the DSL.sum() function takes a Field<? extends Number> Field<? extends Number> argument, so what you want to do needs some tweaking on types. Here are two alternative ways to implement that query:

// Static imports are assumed to be present:
import static org.jooq.impl.DSL.*;

DSLContext ctx = using(configuration);

// Solution 1) Coerce Field<Boolean> to Field<Number>
ctx.select(count(), sum(field(TABLE1.VALUE.gt(100)).coerce(Integer.class)))
   .from(TABLE1)
   .fetch();

// Solution 2) Resort to a raw type cast
ctx.select(count(), sum((Field) field(TABLE1.VALUE.gt(100))))
   .from(TABLE1)
   .fetch();

In both solutions, you will need to transform an org.jooq.Condition into an org.jooq.Field by calling DSL.field(Condition) . This has no effect on the generated SQL when using MySQL which natively supports this kind of usage for boolean types. If you were using a database without support for boolean types, DSL.field(Condition) would generate a CASE expression.

In jOOQ 4.0 ( Issue #3415 ), the DSL.sum() function is scheduled to relax argument type constraints so that the call to coerce() or the cast to (Field) are no longer needed.