What difficulties have you encountered when writing SQL queries or other database queries?

When writing SQL queries, the following difficulties often arise:

• Performance optimization: complex queries with many JOINs, subqueries, or aggregations can run slowly. It is necessary to be able to read execution plans and optimize indexes.
• Data correctness: errors in WHERE or JOIN conditions can lead to incorrect results or duplicate rows.
• Security: it is important to avoid SQL injections, especially when dynamically forming queries. In Go, prepared statements are used for this purpose.
• Understanding the data schema: sometimes it is difficult to understand the relationships between tables, especially in large databases.

An example of a safe query in Go using a prepared statement:

stmt, err := db.Prepare("SELECT name FROM users WHERE age > ?")
if err != nil {
    // handle error
}
rows, err := stmt.Query(30)
// ...

Difficulties can also arise when working with NoSQL databases, where queries and data structures differ from relational databases.