Kuidas diagnoosid ja lahendad SQL-päringute aeglase täitmise põhjuseid?

To diagnose low execution speed of SQL queries in C# projects, I use the following approach:

1. Analysis of the query execution plan — using SQL Server Management Studio (SSMS) or similar tools, I observe how the database management system (DBMS) executes the query, identifying full table scans and lack of indexes.

2. Query profiling — I use SQL Profiler or built-in tools to monitor execution time and blocking.

3. Query optimization — I rewrite queries, remove unnecessary JOINs and subqueries, add necessary indexes.

4. Parameterization check — I avoid dynamic SQL to utilize plan caching.

5. Server load check — I verify if the server is overloaded, if there are blocks or long transactions.

Example of optimization in C# with parameterized query:

using (var connection = new SqlConnection(connectionString))
{
    connection.Open();
    var command = new SqlCommand("SELECT * FROM Users WHERE Age > @age", connection);
    command.Parameters.AddWithValue("@age", 18);
    using (var reader = command.ExecuteReader())
    {
        while (reader.Read())
        {
            // data processing
        }
    }
}

This approach helps identify bottlenecks and improve query performance.