Group

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group by s’utilitza per juntar aquelles files de la taula que tenen el mateix valor en totes les columnes seleccionades.

Quan comences a construir una consulta amb group by ja no pots utilitza `select * from t1p , sino que has de fer servir aquesta plantilla per començar a treballar (on x és la columna que vols fer servir per agrupa les files). D’aquesta manera, també podras veure el número de filas agrupades per cada valor de x.

select x, count(x)
from t1
group by x

Comencen amb un exemple. La función from ens retorna una taula

from test

  x   y
  a   3
  c   2
  b   5
  a   7

group by x

  x   y
  a   3,7
  c   2
  b   5

El resultat són tres grups.

Quines columnes podem seleccionar?

select *
ERROR! El valor y de la fila a no és correcte

El resultat han de ser files: els grups “b” i “c” es poden convertir en files, però com es fa amb el grup “a”?

select x

x a c b

Si elimino la columna y puc convertir tots els grups en files. select x, sum(y)

x sum a 10 b 5 c 2

Si agrego tots el valors y de cada grup, tambè puc convertir els grups en files. Per tant haig de fer servir una funció d’agregació, que rep una llista de valors i en retorna un.

En aquest cas, utilitzo sum.

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Using GROUP BY in SQL Now that you know SQL’s core commands, power up your queries with the GROUP BY clause and aggregate functions.

GROUP BY Clause: How Well Do You Know It?. The database can do different kinds of computations: it can add and subtract, multiply and divide, it can do computations on dates, it can count rows and sum row values, and so on. It can also do quite sophisticated statistics. The GROUP BY clause is the most basic way to compute statistics in SQL. It can be quite tough for beginners but it is really powerful. Let’s look at the details of the GROUP BY clause, starting with the basics.

5 Examples of GROUP BY. When you start learning SQL, you quickly come across the GROUP BY clause. Data grouping—or data aggregation—is an important concept in the world of databases. In this article, we’ll demonstrate how you can use the GROUP BY clause in practice. We’ve gathered five GROUP BY examples, from easier to more complex ones so you can see data grouping in a real-life scenario. As a bonus, you’ll also learn a bit about aggregate functions and the HAVING clause.

SQL HAVING Tutorial. Learn how to use the SQL HAVING clause to filter groups using your own specified conditions.

What Is the SQL HAVING Clause?. Are you learning SQL? Are you wondering what you can use the HAVING clause for? Or, perhaps, have you tried to use WHERE on your GROUP BY aggregates? You are in the right place! In this article, we explain how to use HAVING with plenty of examples.

HAVING vs. WHERE in SQL: What You Should Know. This article is about SQL’s WHERE and HAVING clauses. Both clauses are part of the foundations of the SQL SELECT command. They have similar uses, but there are also important differences that every person who uses SQL should know. Let’s see what’s behind the HAVING vs. WHERE debate.

Sqlite - Group

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