Introdução Consultas individuais respondem perguntas como "qual o email do cliente 42?". Mas as perguntas mais valiosas em qualquer sistema são de outro tipo: "qual o produto mais vendido?", "qual a receita média por pedido?", "quantos clientes se cadastraram esse mês?". Para responder isso, o SQL oferece as funções de agregação — operações que recebem um conjunto de linhas e devolvem um único valor resumido. Para os exemplos a seguir, considere esta tabela: pedidos: | id | cliente | produto | categoria | quantidade | valor | |----|------------|-------------|--------------|------------|--------| | 1 | Ana Lima | Notebook | Eletrônicos | 1 | 3500.00| | 2 | Ana Lima | Mouse | Periféricos | 2 | 80.00| | 3 | Bruno Melo | Teclado | Periféricos | 1 | 150.00| | 4 | Bruno Melo | Notebook | Eletrônicos | 1 | 3500.00| | 5 | Carla Nunes| Monitor | Eletrônicos | 2 | 1200.00| | 6 | Carla Nunes| Mouse | Periféricos | 1 | 80.00| As Funções de Agregação COUNT Conta o número de linhas — ou de valores não nulos em uma coluna específica. -- Total de pedidos SELECT COUNT ( * ) AS total_pedidosFROM pedidos ; -- Resultado: 6 -- Clientes distintos que fizeram pedidos SELECT COUNT ( DISTINCT cliente ) AS clientes_unicosFROM pedidos ; -- Resultado: 3 COUNT(*) conta todas as linhas, incluindo as que têm nulos. COUNT(coluna) conta apenas as linhas onde aquela coluna não é nula. COUNT(DISTINCT coluna) conta valores únicos — útil para saber quantos clientes, produtos ou categorias distintos aparecem no resultado. SUM Soma os valores de uma coluna numérica. -- Receita total SELECT SUM ( valor ) AS receita_total FROM pedidos ; -- Resultado: 8510.00 -- Total de itens vendidos SELECT SUM ( quantidade ) AS itens_vendidos FROM pedidos ; -- Resultado: 8 AVG Calcula a média aritmética dos valores. -- Valor médio por pedido SELECT AVG ( valor ) AS ticket_medio FROM pedidos ; -- Resultado: 1418.33 AVG ignora valores nulos automaticamente — calcula a média apenas sobre os registros que têm valor preenchid

This is a submission for Weekend Challenge: Passion Edition What I Built HahaNotes is an interactive web application designed to help developers, office workers, and students vent their daily stress by transforming real-world struggles (legacy code at 3 AM, unpaid overtime, sếp hãm, or exam stress) into hilarious, sarcastic AI-voiced banters, complete podcasts, and ready-to-share short videos. The application features a dynamic dialogue between two contrasting AI hosts: Rookie (The Naive Optimist): A starry-eyed beginner who sees the world through rose-colored glasses and speaks in trendy buzzwords. Cynic (The Sarcastic Senior): A battle-hardened veteran who gently (or not so gently) pops Rookie's bubble with witty, dry, and highly relatable tech sarcasm. Users can input their struggles, choose their favorite voices for the hosts, generate structured comedy scripts, chat continuously with the hosts to extend the banter, listen to fully produced podcasts with ambient lo-fi background music/laugh tracks, and export 9:16 vertical short videos with synchronized karaoke captions and visual memes. Demo Video Demo: Website Demo: https://hahanotes.vercel.app/ Code omlttg / hahanotes 🎙️ HahaNotes Banishing Developer Burnout with AI Banter Podcasts & Short Videos Live Demo: hahanotes.vercel.app Weekend Challenge: Submitted for Weekend Challenge: Passion Edition 🌟 Introduction HahaNotes is an interactive web application designed to help developers, office workers, and students vent their daily stress by transforming real-world struggles (e.g. legacy bugs at 3 AM, unpaid overtime, or exam anxiety) into hilarious, sarcastic AI-voiced banters, complete podcasts, and ready-to-share short videos. The application features a dialogue between two contrasting AI hosts: Rookie (The Naive Optimist): A starry-eyed beginner who sees the world through rose-colored glasses, uses corporate buzzwords, and believes completely in hustle culture. Cynic (The Sarcastic Senior): A battle-hardened ve

...now, I pride myself on being good at my job, I'm fast at catching mistakes, I'm efficient at...

Hello Hacker News photographers! Yes, this is essentially my take on photo colling and management, similar to the features that Lightroom and Darktable already have. Because I shoot in JPEG+RAW, my workflow looks like me going through my JPEG images and then eliminating the JPEGs I don't like afterwards in addition to their corresponding RAWs. At least on my old MacBook, the JPEGs were faster to load than the RAW photos (probably a combination of CR2, the file my EOS 40D, not having embedded JPE

submitted by /u/actinium226 [link] [留言]