SuperDB

Index

The index operation is denoted with square brackets and can be applied to any indexable data type and has the form:

<entity> [ <index> ]

where <entity> is an expression resulting in an indexable entity and <index> is an expression resulting in a value that is used to index the indexable entity.

Indexable entities include records, arrays, sets, maps, strings, and bytes.

If <entity> is a record, then the <index> operand must be coercible to a string and the result is the record’s field of that name.

If <entity> is an array, then the <index> operand must be coercible to an integer and the result is the value in the array of that index.

If <entity> is a set, then the <index> operand must be coercible to an integer and the result is the value in the set of that index ordered by total order of values.

If <entity> is a map, then the <index> operand is presumed to be a key and the corresponding value for that key is the result of the operation. If no such key exists in the map, then the result is error("missing").

If <entity> is a string, then the <index> operand must be coercible to an integer and the result is an integer representing the unicode code point at that offset in the string.

If <entity> is type bytes, then the <index> operand must be coercible to an integer and the result is an unsigned 8-bit integer representing the byte value at that offset in the bytes sequence.

Note

Indexing of strings and bytes is not yet implemented.

Index Base

Indexing in SuperSQL are 0-based meaning the first element is at index 0 and the last element is at index n-1 for an entity of size n.

If 1-based indexing is desired, a scoped language pragma may be used to specify either 1-based indexing or mixed indexing. In mixed indexing, 0-based indexing is used for expressions appearing in pipe operators and 1-based indexing is used for expressions appearing in SQL operators.

Note

Mixed indexing is not yet implemented.

Examples

Simple index

# spq
values a[2]
# input
{a:[1,2,3,4]}
{a:|[1,2,3,4]|}
{a:"1234"}
{a:0x01020304}
# expected output
3
3
error("missing")
error("missing")

One-based indexing

# spq
pragma index_base = 1
values a[2]
# input
{a:[1,2,3,4]}
{a:|[1,2,3,4]|}
{a:"1234"}
{a:0x01020304}
# expected output
2
2
error("missing")
error("missing")

Index from end of entity

# spq
values a[-1]
# input
{a:[1,2,3,4]}
{a:|[1,2,3,4]|}
{a:"1234"}
{a:0x01020304}
# expected output
4
4
error("missing")
error("missing")