Go Database Best Practices

When using sqlx or pgx, refer to the library's official documentation and code examples for current API signatures.

Best Practices Summary

1. Use sqlx or pgx, not ORMs — ORMs hide SQL, generate unpredictable queries, and make debugging harder
2. Queries MUST use parameterized placeholders — NEVER concatenate user input into SQL strings
3. Context MUST be passed to all database operations — use *Context method variants (QueryContext, ExecContext, GetContext)
4. sql.ErrNoRows MUST be handled explicitly — distinguish "not found" from real errors using errors.Is
5. Rows MUST be closed after iteration — defer rows.Close() immediately after QueryContext calls
6. NEVER use db.Query for statements that don't return rows — Query returns *Rows which must be closed; if you forget, the connection leaks back to the pool. Use db.Exec instead
7. Use transactions for multi-statement operations — wrap related writes in BeginTxx/Commit
8. Use SELECT ... FOR UPDATE when reading data you intend to modify — prevents race conditions
9. Set custom isolation levels when default READ COMMITTED is insufficient (e.g., serializable for financial operations)
10. Handle NULLable columns with pointer fields (*string, *int) or sql.NullXxx types
11. Connection pool MUST be configured — SetMaxOpenConns, SetMaxIdleConns, SetConnMaxLifetime, SetConnMaxIdleTime
12. Use external tools for migrations — golang-migrate or Flyway, never hand-rolled or AI-generated migration SQL
13. Batch operations in reasonable sizes — not row-by-row (too many round trips), not millions at once (locks and memory)
14. Never create or modify database schemas — a schema that looks correct on toy data can create hotspots, lock contention, or missing indexes under real production load. Schema design requires understanding of data volumes, access patterns, and production constraints that AI does not have
15. Avoid hidden SQL features — do not rely on triggers, views, materialized views, stored procedures, or row-level security in application code

Library Choice

Why NOT ORMs:

• Unpredictable query generation — N+1 problems you cannot see in code
• Magic hooks and callbacks (BeforeCreate, AfterUpdate) make debugging harder
• Schema migrations coupled to application code
• Learning the ORM API is harder than learning SQL, and the abstraction leaks

Parameterized Queries

// ✗ VERY BAD — SQL injection vulnerability
query := fmt.Sprintf("SELECT * FROM users WHERE email = '%s'", email)

// ✓ Good — parameterized (PostgreSQL)
var user User
err := db.GetContext(ctx, &user, "SELECT id, name, email FROM users WHERE email = $1", email)

// ✓ Good — parameterized (MySQL)
err := db.GetContext(ctx, &user, "SELECT id, name, email FROM users WHERE email = ?", email)

Dynamic IN clauses

query, args, err := sqlx.In("SELECT * FROM users WHERE id IN (?)", ids)
if err != nil {
    return fmt.Errorf("building IN clause: %w", err)
}
query = db.Rebind(query) // adjust placeholders for your driver
err = db.SelectContext(ctx, &users, query, args...)

Dynamic column names

Never interpolate column names from user input. Use an allowlist:

allowed := map[string]bool{"name": true, "email": true, "created_at": true}
if !allowed[sortCol] {
    return fmt.Errorf("invalid sort column: %s", sortCol)
}
query := fmt.Sprintf("SELECT id, name, email FROM users ORDER BY %s", sortCol)

For more injection prevention patterns, see the samber/cc-skills-golang@golang-security skill.

Struct Scanning and NULLable Columns

Use db:"column_name" tags for sqlx, pgx.CollectRows with pgx.RowToStructByName for pgx. Handle NULLable columns with pointer fields (*string, *time.Time) — they work cleanly with both scanning and JSON marshaling. See Scanning Reference for examples of all approaches.

Error Handling

func GetUser(id string) (*User, error) {
    var user User

    err := db.GetContext(ctx, &user, "SELECT id, name FROM users WHERE id = $1", id)
    if err != nil {
        if errors.Is(err, sql.ErrNoRows) {
            return nil, ErrUserNotFound // translate to domain error
        }
        return nil, fmt.Errorf("querying user %s: %w", id, err)
    }

    return &user, nil
}