我在 couchbase 中创建了一个二级索引:
CREATE INDEX `data` ON `bucket`(`field1`,`field2`,`field3`,
lower(`field4`)) WHERE (`field5` = "CONSTANT")
当我在 couchbase 上执行此查询时:
select document.* from bucket AS document WHERE document.field5 = "CONSTANT"
AND document.field1 = "docId"
and (document.field3 like "%" or
lower(document.field4) like "%");
即使没有给出主要谓词之一(field2)的值,查询似乎仍然可以正常工作。谁能解释为什么?
这是在查询前添加“EXPLAIN”时返回的查询计划:
"#operator": "Sequence",
"~children": [
{
"#operator": "Sequence",
"~children": [
{
"#operator": "IndexScan3",
"as": "document",
"index": "data",
"index_id": "6588bcds21b213",
"index_projection": {
"primary_key": true
},
"keyspace": "bucket",
"namespace": "default",
"spans": [
{
"exact": true,
"range": [
{
"high": "\"docId\"",
"inclusion": 3,
"low": "\"docId\""
}
]
}
],
"using": "gsi"
},
{
"#operator": "Fetch",
"as": "document",
"keyspace": "bucket",
"namespace": "default"
},
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [
{
"#operator": "Filter",
"condition": "((((`document`.`field5`) = \"CONSTANT\") and ((`document`.`field1`) = \"docId\")) and (((`document`.`field3`) like \"%\"]) or (lower((`document`.`field4`)) like \"%\")))"
},
{
"#operator": "Project",
"result_terms": [
{
"expr": "`document`",
"star": true
}
]
}
]
}
}
]
}