SQL Fundamental

  • 1 Create a Postgres Table
  • 2 Insert Data with Insert
  • 3 Filter Data in a Postgres Table with Query Statements
  • 4 Update Data in Table with update
update Users set user_handle = uuid_generate_v4() where last_name = 'clark';
  • 5 Removing Data with Delete, Truncate and Drop
SELECT nameFROM customerWHERE referee_id != 2OR referee_id IS NULL
SELECT name CustomersFROM CustomersWHERE id NOT IN (SELECT customerId FROM Orders)
SELECT column_name(s)
FROM table_name

1699. Number of Calls Between Two Persons

from_id AS person1, to_id AS person2,
COUNT(1) AS call_count, SUM(duration) AS total_duration
FROM calls
GROUP BY LEAST(from_id, to_id), GREATEST(from_id, to_id)



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