¿Cómo agregar juntos los resultados de varias subconsultas?

Question

Estoy ejecutando una consulta MySQL para clasificar a los usuarios de mi sitio de acuerdo con la cantidad de reseñas de libros y reseñas de recetas que han contribuido. Después de los problemas iniciales con una consulta JOIN múltiple, he cambiado a una serie de subconsultas, que es mucho, mucho más rápido. Sin embargo, aunque puedo extraer el número de revisiones de cada miembro, no puedo encontrar la manera de sumarlas para poder ordenar por el número total.

Aquí está la consulta actual:

SELECT users.*, 
    (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
    (SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) as bookreviews, 
    (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID) as recipereviews 
FROM users 

necesito sumar bookreviews y recipereviews para conseguir '' reviewtotals. MySQL no le permitirá usar sintaxis simple para hacer cálculos en alias, pero supongo que hay otra manera de hacer esto.

Answer 1

envolverlo en una subconsulta:

SELECT *, 
     bookreviews + recipereviews AS totalreviews 
FROM (
     SELECT users.*, 
       (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
       (SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) as bookreviews, 
       (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID) as recipereviews 
     FROM users 
     ) q 

Answer 2

¿Ha intentado lo siguiente?

SELECT users.*, 
    (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
    ((SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) + 
    (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID)) as reviewtotal 
FROM users 

Answer 3

Dos opciones:

Opción 1: feo es el infierno, y probablemente lenta (depende de la caché de consultas):

SELECT users.*, 
    (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
    (SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) as bookreviews, 
    (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID) as recipereviews 
    (SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) + (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID) as reviewtotals 
FROM users 

Opción 2: guardar los resultados en una tabla temporal y a continuación, consulta esta tabla

Tal vez esto va a funcionar (no lo he probado)

SELECT *, bookreviews+recipereviews as reviewtotals FROM 
(SELECT users.*, 
    (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
    (SELECT count(*) FROM book_reviews WHERE book_reviews.user_id = users.ID) as bookreviews, 
    (SELECT count(*) FROM recipe_reviews WHERE recipe_reviews.user_id = users.ID) as recipereviews 
FROM users) u 

Answer 4

Si usted quiere estar seguro y rápido, hacerlo de esta manera:

SELECT users.* 
,  titles.num       titles 
,  book_reviews.num      book_reviews 
,  recipe_reviews.num     recipe_reviews 
,  book_reviews.num + recipe_reviews.num total_reviews 
FROM  users 
LEFT JOIN (
      SELECT user_ID, count(*) AS num 
      FROM  bookshelf 
      GROUP BY user_ID 
     ) as titles 
ON  users.ID = titles.user_ID 
LEFT JOIN (
      SELECT user_ID, count(*) AS num 
      FROM  book_reviews 
      GROUP BY user_ID 
     ) as book_reviews 
ON  users.ID = reviews.user_ID 
LEFT JOIN (
      SELECT user_ID, count(*) AS num 
      FROM  recipe_reviews 
      GROUP BY user_ID 
     ) as recipe_reviews 
ON  users.ID = recipes.user_ID 

Si usted quiere meter a las subconsultas en la lista SELECT, y quiere que sea seguro, eche un vistazo a la solución de Quassnoi.

Si te gusta vivir un poco dangersouly y todavía quieren un resultado rápido, puede utilizar las variables definidas por el usuario. Mi predicción es que estará seguro en este caso muy particular:

SELECT users.*, 
     (SELECT count(*) FROM bookshelf WHERE bookshelf.user_id = users.ID) as titles, 
     @bookreviews:=(
      SELECT count(*) 
      FROM book_reviews 
      WHERE book_reviews.user_id = users.ID 
     ) as bookreviews, 
     @recipereviews:=(
      SELECT count(*) 
      FROM recipe_reviews 
      WHERE recipe_reviews.user_id = users.ID 
     ) as recipereviews, 
     @bookreviews + @recipereviews as total_reviews 
FROM users