Use EXISTS to check if a row is present

Need to find if records from table A can also be found in table B? EXISTS is here to help.

📌 Here's the syntax.
𝚂𝙴𝙻𝙴𝙲𝚃 * 𝙵𝚁𝙾𝙼 𝚝𝚊𝚋𝚕𝚎_𝚊
𝚆𝙷𝙴𝚁𝙴 𝙴𝚇𝙸𝚂𝚃𝚂 (
𝚂𝙴𝙻𝙴𝙲𝚃 * 𝙵𝚁𝙾𝙼 𝚝𝚊𝚋𝚕𝚎_𝚋
𝚆𝙷𝙴𝚁𝙴 𝚝𝚊𝚋𝚕𝚎_𝚊.𝚔𝚎𝚢 = 𝚝𝚊𝚋𝚕𝚎_𝚋.𝚔𝚎𝚢
) 𝚒𝚗𝚗𝚎𝚛_𝚚𝚞𝚎𝚛𝚢

Let's walk through this.
1️⃣ the inner query retrieves all the records from table_b that has a common key with table_a.
2️⃣ If the inner query returns any records, the output is simply the the records found in both tables A and B. Otherwise, the query returns no records.

EXISTS is useful when one needs to implement UPDATE/DELETE of rows in one table.

🚀 There are multiple ways of implementing the same results. Give it a try! Write the equivalent query using "INNER JOIN" or the "IN" operator in the comment section below.

EXISTS can be used in most RDBMS, including PostgreSQL, MySQL, Oracle, Redshift and Google BigQuery.

👇 Full example below.