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ВЫБЕРИТЕ внутри COUNT

Я хотел бы встроить SELECT внутри COUNT, но я не могу найти никаких примеров.

#pseudosql
SELECT a AS current_a, COUNT(*) AS b,
   COUNT( SELECT FROM t WHERE a = current_a AND c = 'const' ) as d,
   from t group by a order by b desc

Ответ 1

Вам не нужен суб-выбор:

SELECT a, COUNT(*) AS b,
   SUM( CASE WHEN c = 'const' THEN 1 ELSE 0 END ) as d,
   from t group by a order by b desc

Ответ 2

Вы можете переместить count() внутри своего подвыборки:

SELECT a AS current_a, COUNT(*) AS b,
   ( SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d,
   from t group by a order by b desc

Ответ 3

Используйте SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d.

Ответ 4

SELECT a AS current_a, COUNT(*) AS b,
   (SELECT COUNT(*) FROM t WHERE a = current_a AND c = 'const' ) as d
   from t group by a order by b desc