{
    "api": "YAML JSON TOON Database",
    "version": "1.0.0",
    "format": "json",
    "dataset": {
        "id": 1009,
        "slug": "sql-index-patterns",
        "title": "PostgreSQL Index Design Patterns",
        "description": "Index choices for equality, ordered retrieval, selective predicates, and specialized PostgreSQL workloads.",
        "summary": "Index choices for equality, ordered retrieval, selective predicates, and specialized PostgreSQL workloads. Each row includes a practical application and a failure to check before using it.",
        "use_when": [
            "Choose an index from a real filter and sort.",
            "Explain why an added index did not help a query."
        ],
        "caveats": [
            "Planner choices depend on table size, statistics, and data distribution.",
            "Extra indexes consume space and slow writes."
        ],
        "related": [
            "sql-window-functions",
            "database-isolation-anomalies"
        ],
        "category": "Database Types",
        "category_slug": "database-types",
        "tags": "database-types,sql index patterns,reference,engineering",
        "view_count": 0,
        "created_at": 1791798640,
        "updated_at": 1791798640,
        "reviewed_at": "2026-10-12",
        "sources": [
            {
                "title": "PostgreSQL index types",
                "url": "https://www.postgresql.org/docs/current/indexes-types.html"
            },
            {
                "title": "PostgreSQL multicolumn indexes",
                "url": "https://www.postgresql.org/docs/current/indexes-multicolumn.html"
            },
            {
                "title": "PostgreSQL EXPLAIN",
                "url": "https://www.postgresql.org/docs/current/using-explain.html"
            }
        ],
        "reading": [
            "choose-sql-indexes-from-query-plans"
        ],
        "provenance": "Original editorial reference notes by YJTOON, informed by the linked primary documentation. External specifications retain their own licenses.",
        "entry_count": 10,
        "fields": [
            {
                "section": "data",
                "field": "pattern",
                "type": "string",
                "example": "B-tree equality"
            },
            {
                "section": "data",
                "field": "example",
                "type": "string",
                "example": "CREATE INDEX ON events (user_id)"
            },
            {
                "section": "data",
                "field": "use",
                "type": "string",
                "example": "Look up rows by a frequently filtered value."
            },
            {
                "section": "data",
                "field": "tradeoff",
                "type": "string",
                "example": "Low-selectivity filters may still favor a seque…"
            }
        ]
    },
    "data": [
        {
            "pattern": "B-tree equality",
            "example": "CREATE INDEX ON events (user_id)",
            "use": "Look up rows by a frequently filtered value.",
            "tradeoff": "Low-selectivity filters may still favor a sequential scan."
        },
        {
            "pattern": "Composite index",
            "example": "CREATE INDEX ON events (user_id, created_at)",
            "use": "Support a user filter followed by ordered time access.",
            "tradeoff": "Column order should follow the real query shape."
        },
        {
            "pattern": "Unique index",
            "example": "CREATE UNIQUE INDEX ON users (email)",
            "use": "Enforce a uniqueness rule with lookup support.",
            "tradeoff": "Case and null semantics must match the domain."
        },
        {
            "pattern": "Partial index",
            "example": "CREATE INDEX ON jobs (created_at) WHERE state = 'pending'",
            "use": "Index only the active subset of a large table.",
            "tradeoff": "The query predicate must imply the index predicate."
        },
        {
            "pattern": "Expression index",
            "example": "CREATE INDEX ON users (lower(email))",
            "use": "Index a repeated expression used by a query.",
            "tradeoff": "The expression adds work to writes."
        },
        {
            "pattern": "Covering index",
            "example": "CREATE INDEX ON orders (customer_id) INCLUDE (total)",
            "use": "Make selected payload columns available to index-only scans.",
            "tradeoff": "Heap visibility can still require heap access."
        },
        {
            "pattern": "BRIN",
            "example": "CREATE INDEX ON logs USING brin (created_at)",
            "use": "Summarize large physically correlated tables.",
            "tradeoff": "Poor physical correlation reduces usefulness."
        },
        {
            "pattern": "GIN array",
            "example": "CREATE INDEX ON docs USING gin (tags)",
            "use": "Support membership-style queries on supported values.",
            "tradeoff": "Write cost and operator classes matter."
        },
        {
            "pattern": "GiST range",
            "example": "CREATE INDEX ON bookings USING gist (during)",
            "use": "Support range overlap with a matching operator class.",
            "tradeoff": "It is not a universal replacement for B-tree."
        },
        {
            "pattern": "Measure the plan",
            "example": "EXPLAIN (ANALYZE, BUFFERS) SELECT ...",
            "use": "Compare estimated and actual work.",
            "tradeoff": "ANALYZE executes the statement; do not run unsafe writes casually."
        }
    ]
}