"covering index" meaning in English

{
  "forms": [
    {
      "form": "covering indexes",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "covering index (plural covering indexes)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Entries with translation boxes",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with French translations",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Databases",
          "orig": "en:Databases",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "bold_text_offsets": [
            [
              20,
              34
            ],
            [
              170,
              184
            ]
          ],
          "ref": "2003, Peter Gulutzan, Trudy Pelzer, SQL Performance Tuning, Addison-Wesley Professional, →ISBN, page 232:",
          "text": "Ordinarily, using a covering index will save one disk read (GAIN: 6/8). The gain is automatic but only if the columns in the select list exactly match the columns in the covering index.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A database table index that contains all the columns needed to fulfill the query."
      ],
      "id": "en-covering_index-en-noun-ivqtx~4O",
      "links": [
        [
          "database",
          "database"
        ],
        [
          "table",
          "table"
        ],
        [
          "index",
          "index"
        ],
        [
          "query",
          "query"
        ]
      ],
      "raw_glosses": [
        "(databases) A database table index that contains all the columns needed to fulfill the query."
      ],
      "topics": [
        "computing",
        "databases",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "sciences"
      ],
      "translations": [
        {
          "code": "fr",
          "lang": "French",
          "sense": "Translations",
          "tags": [
            "masculine"
          ],
          "word": "index couvrant"
        }
      ]
    }
  ],
  "word": "covering index"
}

{
  "forms": [
    {
      "form": "covering indexes",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "covering index (plural covering indexes)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "Entries with translation boxes",
        "Pages with 1 entry",
        "Pages with entries",
        "Terms with French translations",
        "Translation table header lacks gloss",
        "en:Databases"
      ],
      "examples": [
        {
          "bold_text_offsets": [
            [
              20,
              34
            ],
            [
              170,
              184
            ]
          ],
          "ref": "2003, Peter Gulutzan, Trudy Pelzer, SQL Performance Tuning, Addison-Wesley Professional, →ISBN, page 232:",
          "text": "Ordinarily, using a covering index will save one disk read (GAIN: 6/8). The gain is automatic but only if the columns in the select list exactly match the columns in the covering index.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A database table index that contains all the columns needed to fulfill the query."
      ],
      "links": [
        [
          "database",
          "database"
        ],
        [
          "table",
          "table"
        ],
        [
          "index",
          "index"
        ],
        [
          "query",
          "query"
        ]
      ],
      "raw_glosses": [
        "(databases) A database table index that contains all the columns needed to fulfill the query."
      ],
      "topics": [
        "computing",
        "databases",
        "engineering",
        "mathematics",
        "natural-sciences",
        "physical-sciences",
        "sciences"
      ]
    }
  ],
  "translations": [
    {
      "code": "fr",
      "lang": "French",
      "sense": "Translations",
      "tags": [
        "masculine"
      ],
      "word": "index couvrant"
    }
  ],
  "word": "covering index"
}