{
  "$schema": "https://myflames.dev/schemas/sidecar-v1.json",
  "schema_version": "1.3",
  "generated_at": "2026-04-25T12:51:27Z",
  "myflames_version": "1.5.0",
  "source": {
    "type": "file",
    "engine": "mysql",
    "fixture_path": "/Users/viniciusgrippa/Downloads/git/myflames/test/mysql-explain-weedout.json"
  },
  "plan_summary": {
    "total_time_ms": 0.352,
    "rows_sent": 49,
    "rows_examined_estimate": 2001,
    "operator_count": 5,
    "max_depth": 4
  },
  "optimizer_switches": [
    {
      "name": "semijoin",
      "value": "on",
      "explanation": "IN / EXISTS subqueries are rewritten into a semi-join with the outer query and then resolved via one of the semijoin strategies (firstmatch, loosescan, duplicateweedout, or materialization).",
      "node_labels": [
        "Remove duplicate t1 rows using temporary table (we..."
      ]
    },
    {
      "name": "duplicateweedout",
      "value": "on",
      "explanation": "Semijoin strategy: runs the subquery as a normal inner join and then removes duplicate outer rows using a temporary table keyed on their row IDs.",
      "node_labels": [
        "Remove duplicate t1 rows using temporary table (we..."
      ]
    }
  ],
  "warnings": [
    {
      "severity": "warn",
      "category": "full_scan",
      "text": "Full table scan: t2 (2000 rows)",
      "source": "plan",
      "node_labels": [
        "Table scan [t2]"
      ]
    }
  ],
  "suggestions": [
    {
      "severity": "high",
      "category": "index",
      "action": "Add indexes on filter/join columns to avoid full table scans",
      "source": "plan"
    }
  ],
  "executive_summary": "Query scans 1 table; examines ~2,001 rows to return 49 in 0.35 ms. Main finding: no index covers (y, x) on t2.",
  "plan_tree": {
    "node_id": "n:0fc991f45412",
    "short_label": "Remove duplicate t1 rows using temporary table (we...",
    "folded_label": "Remove duplicate t1 rows using temporary table (weedout) starts=1 rows=49",
    "children": [
      {
        "node_id": "n:e32c3e0bcf9b",
        "short_label": "Nested loop inner join",
        "folded_label": "NESTED LOOP INNER starts=1 rows=49",
        "children": [
          {
            "node_id": "n:215e07533821",
            "short_label": "Filter: (((t2.y < 100) and (t2.x is not null)))",
            "folded_label": "FILTER (((t2.y < 100) and (t2.x is not null))) starts=1 rows=49",
            "children": [
              {
                "node_id": "n:39a4125027ad",
                "short_label": "Table scan [t2]",
                "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
                "children": []
              }
            ]
          },
          {
            "node_id": "n:5c9e8b01da7e",
            "short_label": "Single-row lookup [t1.PRIMARY]",
            "folded_label": "SINGLE ROW LOOKUP [t1.PRIMARY] starts=49 rows=1",
            "children": []
          }
        ]
      }
    ]
  },
  "query": {
    "raw": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))",
    "beautified": "select testdb.t1.id AS id,testdb.t1.a AS a,testdb.t1.b AS b,testdb.t1.c AS c,testdb.t1.d AS d\nfrom testdb.t1 semi\n  join (testdb.t2)\nwhere ((testdb.t1.id = testdb.t2.x) and (testdb.t2.y < 100))"
  },
  "index_suggestions": [
    {
      "table": "t2",
      "columns": [
        "y",
        "x"
      ],
      "ddl": "CREATE INDEX idx_t2_y_x ON t2 (y, x);",
      "reason": "Full scan on t2 with filter on (y, x)"
    }
  ],
  "primary_action": {
    "ref": "suggestions[0]"
  },
  "teach_hooks": [
    {
      "lesson": "semijoin_weedout",
      "match": {
        "folded_label": "Remove duplicate t1 rows using temporary table (weedout) starts=1 rows=49",
        "short_label": "Remove duplicate t1 rows using temporary table (we..."
      },
      "controls": {
        "outer_rows": 49,
        "inner_matches": 5,
        "row_size": 200
      },
      "note": "Remove duplicate t1 rows using temporary table (weedout)",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))"
    },
    {
      "lesson": "nested_loop",
      "match": {
        "folded_label": "NESTED LOOP INNER starts=1 rows=49",
        "short_label": "Nested loop inner join"
      },
      "controls": {
        "outer_rows": 49,
        "inner_rows": 49,
        "row_size": 200
      },
      "note": "Nested loop inner join",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))"
    },
    {
      "lesson": "filter",
      "match": {
        "folded_label": "FILTER (((t2.y < 100) and (t2.x is not null))) starts=1 rows=49",
        "short_label": "Filter: (((t2.y < 100) and (t2.x is not null)))"
      },
      "controls": {
        "input_rows": 49,
        "selectivity": 7.4
      },
      "note": "Filter: ((t2.y < 100) and (t2.x is not null))",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))"
    },
    {
      "lesson": "full_scan",
      "match": {
        "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
        "short_label": "Table scan [t2]"
      },
      "controls": {
        "rows": 2000,
        "row_size": 200,
        "selectivity": 100.0
      },
      "note": "Table scan on t2 (t2)",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))"
    },
    {
      "lesson": "unique_lookup",
      "match": {
        "folded_label": "SINGLE ROW LOOKUP [t1.PRIMARY] starts=49 rows=1",
        "short_label": "Single-row lookup [t1.PRIMARY]"
      },
      "controls": {
        "rows": 49,
        "covering": false
      },
      "note": "Single-row index lookup on t1 using PRIMARY (id=t2.x) (t1)",
      "query_sql": "/* select#1 */ select `testdb`.`t1`.`id` AS `id`,`testdb`.`t1`.`a` AS `a`,`testdb`.`t1`.`b` AS `b`,`testdb`.`t1`.`c` AS `c`,`testdb`.`t1`.`d` AS `d` from `testdb`.`t1` semi join (`testdb`.`t2`) where ((`testdb`.`t1`.`id` = `testdb`.`t2`.`x`) and (`testdb`.`t2`.`y` < 100))"
    }
  ],
  "operator_complexities": [
    {
      "node_id": "n:0fc991f45412",
      "folded_label": "Remove duplicate t1 rows using temporary table (weedout) starts=1 rows=49",
      "short_label": "Remove duplicate t1 rows using temporary table (we...",
      "complexity": {
        "big_o": "O(n log n)",
        "short": "n log n",
        "severity": "medium",
        "rationale": "DuplicateWeedout semijoin: runs as a plain inner join, then drops duplicates using a temp-table index on the outer row IDs.",
        "confidence": "typical",
        "learn_more": "duplicate_weedout"
      }
    },
    {
      "node_id": "n:e32c3e0bcf9b",
      "folded_label": "NESTED LOOP INNER starts=1 rows=49",
      "short_label": "Nested loop inner join",
      "complexity": {
        "big_o": "O(n · log m)",
        "short": "n · log m",
        "severity": "medium",
        "rationale": "Indexed nested loop: each outer row probes the inner table via an index descent.",
        "confidence": "exact",
        "learn_more": "nested_loop_join"
      }
    },
    {
      "node_id": "n:39a4125027ad",
      "folded_label": "TABLE SCAN [t2] starts=1 rows=2000",
      "short_label": "Table scan [t2]",
      "complexity": {
        "big_o": "O(n)",
        "short": "n",
        "severity": "medium",
        "rationale": "Full table scan: the storage engine returns every row; cost scales with the table size.",
        "confidence": "exact",
        "learn_more": "full_table_scan"
      }
    },
    {
      "node_id": "n:5c9e8b01da7e",
      "folded_label": "SINGLE ROW LOOKUP [t1.PRIMARY] starts=49 rows=1",
      "short_label": "Single-row lookup [t1.PRIMARY]",
      "complexity": {
        "big_o": "O(log n)",
        "short": "log n",
        "severity": "good",
        "rationale": "Unique-key lookup (eq_ref): one B+tree descent into the inner table per outer row — as fast as MySQL can get.",
        "confidence": "exact",
        "learn_more": "single_row_lookup"
      }
    }
  ]
}