01. Steps in SQL Query Execution (MySQL)

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Steps in SQL Query Execution (MySQL)


1. Client Sends Query to Server

  • The SQL statement is sent to the MySQL server over a connection (e.g., via JDBC or a query tool like MySQL Workbench).

2. Parser / Syntax Check

  • The parser checks the SQL syntax.If there are any syntax errors, it throws an error immediately.

3. Pre-processor

  • Verifies privileges and permissions for the user executing the query.
  • Resolves object names (like table or column aliases).

4. Query Optimization

  • The optimizer evaluates multiple strategies to execute the query. It considers:

Which indexes to use.

Join order (for multi-table queries).

Whether to use temporary tables.

Cost of different execution paths.

  • The optimizer chooses select the most efficient query plan (Cost effective -> memory, CPU etc).

5. Query Execution Plan (Most cost effective query plan)

  • The query plan is a blueprint of how MySQL will fetch the data.
  • You can view this with the EXPLAIN keyword in front of your query.

6. Query Execution

  • The storage engine (like InnoDB) executes the plan:  
                  Reads from indexes or full table scans. Performs joins, filters, sorts, etc.

7. Result Sent to Client

  • The result set is sent back to the client in chunks.

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