針對多個屬性使用範圍和不等式篩選條件，將查詢最佳化

本頁面提供索引策略範例，可用於對多個欄位套用範圍和不等於篩選器的查詢，打造高效率的查詢體驗。

在最佳化查詢之前，請先瞭解多個屬性的範圍和不等式篩選器概念。

使用「查詢說明」功能最佳化查詢

如要判斷使用的查詢和索引是否最佳化，您可以透過 Query Explain 建立查詢，並查看執行摘要。

Java

...
// Build the query
Query<Entity> query =
    Query.newEntityQueryBuilder()
        .setKind("employees")
        .setFilter(
            CompositeFilter.and(
                PropertyFilter.gt("salary", 100000), PropertyFilter.gt("experience", 0)))
        .setOrderBy(OrderBy("experience"), OrderBy("salary"))
        .build();

// Set the explain options to get back *only* the plan summary
QueryResults<Entity> results = datastore.run(query, ExplainOptions.newBuilder().build());

// Get the explain metrics
Optional<ExplainMetrics> explainMetrics = results.getExplainMetrics();
if (!explainMetrics.isPresent()) {
  throw new Exception("No explain metrics returned");
}

// Get the plan summary
PlanSummary planSummary = explainMetrics.get().getPlanSummary();
List<Map<String, Object>> indexesUsed = planSummary.getIndexesUsed();
System.out.println("----- Indexes Used -----");
indexesUsed.forEach(map -> map.forEach((s, o) -> System.out.println(s + ": " + o)));

// Get the execution stats
if (!explainMetrics.getExecutionStats().isPresent()) {
  throw new Exception("No execution stats returned");
}

ExecutionStats queryStats = explainMetrics.getExecutionStats().get();
Map<String, Object> debugStats = queryStats.getDebugStats();
System.out.println("----- Debug Stats -----");
debugStats.forEach((s, o) -> System.out.println(s + ": " + o));

以下範例說明如何使用正確的索引排序，減少 Firestore (Datastore 模式) 掃描的實體數量。

簡單查詢

以先前的員工集合範例來說，使用 (salary, experience) 索引執行的簡單查詢如下：

GQL

SELECT *
FROM /employees
WHERE salary > 100000 AND experience > 0
ORDER BY experience, salary;

Java

Query<Entity> query =
   Query.newEntityQueryBuilder()
    .setKind("employees")
    .setFilter(
        CompositeFilter.and(
            PropertyFilter.gt("salary", 100000), PropertyFilter.gt("experience", 0)))
    .setOrderBy(OrderBy("experience"), OrderBy("salary"))
    .build();

查詢只掃描 95,000 個索引項目，即可傳回 5 個實體。系統讀取大量索引項目，但因不符合查詢述詞而遭到篩除。

// Output query planning info
{
        "indexesUsed": [
            {
                "query_scope": "Collection Group",
                "properties": "(experience ASC, salary ASC, __name__ ASC)"
            }
        ]
    },
    // Output Query Execution Stats
    {
        "resultsReturned": "5",
        "executionDuration": "2.5s",
        "readOperations": "100",
        "debugStats": {
            "index_entries_scanned": "95000",
            "documents_scanned": "5",
            "billing_details": {
                "documents_billable": "5",
                "index_entries_billable": "95000",
                "small_ops": "0",
                "min_query_cost": "0"
            }
        }
    }

如先前的範例所示，我們可以推斷 salary 限制比 experience 限制更具選擇性。

GQL

SELECT *
FROM /employees
WHERE salary > 100000 AND experience > 0
ORDER BY salary, experience;

Java

Query<Entity> query =
   Query.newEntityQueryBuilder()
    .setKind("employees")
    .setFilter(
        CompositeFilter.and(
            PropertyFilter.gt("salary", 100000), PropertyFilter.gt("experience", 0)))
    .setOrderBy(OrderBy("salary"), OrderBy("experience"))
    .build();

如果您明確使用 orderBy() 子句，以先前的順序新增述詞，Datastore 模式的 Firestore 就會使用 (salary, experience) 索引執行查詢。由於第一個範圍篩選條件的選取範圍比先前的查詢更合適，因此查詢執行速度更快，且成本效益更高。

    // Output query planning info
{
    "indexesUsed": [
        {
            "query_scope": "Collection Group",
            "properties": "(salary ASC, experience ASC, __name__ ASC)"
        }
    ],
    // Output Query Execution Stats
        "resultsReturned": "5",
        "executionDuration": "0.2s",
        "readOperations": "6",
        "debugStats": {
            "index_entries_scanned": "1000",
            "documents_scanned": "5",
            "billing_details": {
                "documents_billable": "5",
                "index_entries_billable": "1000",
                "small_ops": "0",
                "min_query_cost": "0"
            }
        }
    }

後續步驟