Query 4: Using the primary index
Fetch the name and routing details of all male
passengers.
SELECT fullname,bag.bagInfo[].routing FROM BaggageInfo bag
WHERE gender!="F"
Plan:
{
"iterator kind" : "RECEIVE",
"distribution kind" : "ALL_PARTITIONS",
"input iterator" :
{
"iterator kind" : "SELECT",
"FROM" :
{
"iterator kind" : "TABLE",
"target table" : "BaggageInfo",
"row variable" : "$$bag",
"index used" : "primary index",
"covering index" : false,
"index scans" : [
{
"equality conditions" : {},
"range conditions" : {}
}
]
},
"FROM variable" : "$$bag",
"WHERE" :
{
"iterator kind" : "NOT_EQUAL",
"left operand" :
{
"iterator kind" : "FIELD_STEP",
"field name" : "gender",
"input iterator" :
{
"iterator kind" : "VAR_REF",
"variable" : "$$bag"
}
},
"right operand" :
{
"iterator kind" : "CONST",
"value" : "F"
}
},
"SELECT expressions" : [
{
"field name" : "fullname",
"field expression" :
{
"iterator kind" : "FIELD_STEP",
"field name" : "fullname",
"input iterator" :
{
"iterator kind" : "VAR_REF",
"variable" : "$$bag"
}
}
},
{
"field name" : "routing",
"field expression" :
{
"iterator kind" : "ARRAY_CONSTRUCTOR",
"conditional" : true,
"input iterators" : [
{
"iterator kind" : "FIELD_STEP",
"field name" : "routing",
"input iterator" :
{
"iterator kind" : "ARRAY_FILTER",
"input iterator" :
{
"iterator kind" : "FIELD_STEP",
"field name" : "bagInfo",
"input iterator" :
{
"iterator kind" : "VAR_REF",
"variable" : "$$bag"
}
}
}
}
]
}
}
]
}
}
Explanation:
- The root iterator of this query plan is a RECEIVE iterator with a single child (input iterator) that is a SELECT iterator.
- The value of the
FROM
field is an iterator; in this case, it is a TABLE iterator. - The primary key index is used and the index is not covering ( as you need to scan the table to fetch columns other than the index entries).
- The FROM variable is the name of a variable ranging over the records produced by
the FROM iterator. Here the FROM iterator is a TABLE iterator, and the FROM
variable (
$$bag
) is the same as the row variable of the TABLE iterator, as the index used is not covering. - In the SELECT expression two fields
(
fullname,bag.bagInfo[].routing
) are fetched. These correspond to two field names and field expressions in the SELECT expression clause. For the first field, the field expression is computed usingFIELD_STEP
iterator. For the second field, anARRAY_CONSTRUCTOR
iterator is used which iterates over the corresponding array to fetch the field value.