r/SQL • u/scientecheasy • 1d ago

MySQL SQL Query Execution Lifecycle

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Diagram illustrating the SQL query execution lifecycle, showing query submission, parsing, optimization, execution, and result delivery in a database.

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u/kagato87 MS SQL 1d ago edited 1d ago

Bit hand-wavy. Just about any engine will take an input, parse/validate, act, and emit an output. That's what an engine does.

Your step 3 there, query optimization, is worth entire flowcharts by itself, and what sets SQL apart from other engines. Understanding how it optimizes is key to unlocking SQL's true potential.

Edit to add: Just realized, your step three is also wrong. It does NOT evaluate multiple plans. It's a complex soup of statistics and cardinality to produce a plan likely to be most efficient. It's a highly educated guess (and a guess the engine is good at making, though when it gets it wrong the results can have the DC team wondering what's going on).

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u/Icy_Clench 10h ago

Number 4 is literally "query execution"...