SQL Query Order of Execution - System Design

SQL queries are not executed in the same order that they are written by the programmer.

The database engine follows a specific sequence to filter and organize the data efficiently.

It starts with the FROM and JOIN clauses to identify the tables and combine the data.

Next it applies the WHERE clause to filter out individual rows that do not meet the criteria.

The GROUP BY clause then gathers the remaining rows into summary groups.

The HAVING clause is applied after grouping to filter those specific groups.

Only after these steps does the SELECT clause run to determine which columns to display.

The DISTINCT keyword is then used to remove any duplicate rows from the results.

The ORDER BY clause follows to sort the final list in a specific direction.

Finally the LIMIT or OFFSET clauses are applied to return the exact number of rows requested.

Видео SQL Query Order of Execution - System Design канала Greg Hogg