JOOQ-选择查询中的选择计数

Question

I have a problem while converting the following statement into jooq API :

SELECT t1.col1, t1.col2, t1.col3, (SELECT count(*) FROM table2 where table2.col2 = t1.col1)
FROM table1 t1

I tried it with DSL.count() and DSL.selectCount() but I failed while searching a way to add the where clause to the count subquery.

The database is PostgreSQL 9.6.

Answer 1

Lukas suggestion to use DSL.field is the better solution because it preserves the <T> type.

More typesafe version:

TableField<Table1Record, Long> col1 = TABLE1.COL1;
Field<Integer> count = DSL.field(DSL.selectCount().from(TABLE2).where(TABLE2.COL2.eq(col1)));
using(configuration).select(col1, count).from(TABLE1).fetch();

My first (less typesafe) solution:

TableField<Table1Record, Long> col1 = TABLE1.COL1;
Field count = DSL.selectCount().from(TABLE2).where(TABLE2.COL2.eq(col1)).asField("count");
using(configuration).select(col1, count).from(TABLE1).fetch();

Maybe there is a more elegant solution, but it works. The generated query looks like my original query.

Answer 2

Here is another example using DSL.field(...) :

     Field<Integer> COUNT = DSL.field("COUNT(*) OVER ()", Integer.class);

     List<Map<String, Object>> records = DSL.select(ACCESSORY.ID,
                ACCESSORY.NAME,
                ACCESSORY.TYPE,
                ACCESSORY.PRICE,
                BRAND.NAME,
                COUNT.as("total"))
            .from(ACCESSORY)
            .innerJoin(BRAND).onKey()
            .fetchMaps();

The ResultSet will contain a column called total which will be treated as a type java.lang.Integer . This works with PostgreSQL 9.6.

A detailed description of COUNT(*) OVER () can be found here: here .