Struct QueryHints 

pub struct QueryHints {
    pub indexes: SmallVec<[IndexHint; 4]>,
    pub parallel_workers: Option<u32>,
    pub join_hints: SmallVec<[JoinHint; 4]>,
    pub no_seq_scan: bool,
    pub no_index_scan: bool,
    pub cte_materialized: Option<bool>,
    pub timeout_ms: Option<u64>,
    pub custom: Vec<String>,
}

Query plan hints for optimizing complex queries.

These hints are applied to queries to guide the query planner:

• Index hints to force specific index usage
• Parallelism settings
• Join strategies
• Materialization preferences

Database Support

Hint Type	PostgreSQL	MySQL	SQLite	MSSQL
Index	✅ (GUC)	✅	✅	✅
Parallel	✅	❌	❌	✅
Join	✅	✅	❌	✅
CTE Mat	✅	❌	❌	❌

Example

use prax_query::db_optimize::QueryHints;
use prax_query::sql::DatabaseType;

let hints = QueryHints::new()
    .index_hint("users_email_idx")
    .parallel(4)
    .no_seq_scan();

let sql = hints.apply_to_query("SELECT * FROM users WHERE email = $1", DatabaseType::PostgreSQL);

Fields

indexes: SmallVec<[IndexHint; 4]>

Index hints.

parallel_workers: Option<u32>

Parallelism level (0 = default, >0 = specific workers).

join_hints: SmallVec<[JoinHint; 4]>

Join method hints.

no_seq_scan: bool

Whether to prevent sequential scans.

no_index_scan: bool

Whether to prevent index scans.

cte_materialized: Option<bool>

CTE materialization preference.

timeout_ms: Option<u64>

Query timeout in milliseconds.

custom: Vec<String>

Custom database-specific hints.

Implementations

impl QueryHints

pub fn new() -> Self

Create new empty hints.

pub fn index_hint(self, index_name: impl Into<String>) -> Self

Add an index hint.

pub fn index_hint_for_table( self, table: impl Into<String>, index_name: impl Into<String>, ) -> Self

Add an index hint for a specific table.

pub fn ignore_index(self, index_name: impl Into<String>) -> Self

Ignore a specific index.

pub fn parallel(self, workers: u32) -> Self

Set parallelism level.

pub fn no_parallel(self) -> Self

Disable parallel execution.

pub fn no_seq_scan(self) -> Self

Prevent sequential scans.

pub fn no_index_scan(self) -> Self

Prevent index scans.

pub fn cte_materialized(self, materialized: bool) -> Self

Set CTE materialization preference.

pub fn nested_loop_join(self, tables: Vec<String>) -> Self

Force nested loop join.

pub fn hash_join(self, tables: Vec<String>) -> Self

Force hash join.

pub fn merge_join(self, tables: Vec<String>) -> Self

Force merge join.

pub fn timeout(self, ms: u64) -> Self

Set query timeout.

pub fn custom_hint(self, hint: impl Into<String>) -> Self

Add a custom database-specific hint.

pub fn to_sql_prefix(&self, db_type: DatabaseType) -> String

Generate hints as SQL prefix for the given database.

pub fn to_sql_suffix(&self, db_type: DatabaseType) -> String

Generate hints as SQL suffix (for query options).

pub fn apply_to_query(&self, query: &str, db_type: DatabaseType) -> String

Apply hints to a query.

pub fn has_hints(&self) -> bool

Check if any hints are configured.

Trait Implementations

impl Clone for QueryHints

fn clone(&self) -> QueryHints

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for QueryHints

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for QueryHints

fn default() -> QueryHints

Returns the “default value” for a type.