JSON index can be applied to JSON string columns to accelerate the value lookup and filtering for the column.
JSON string can be used to represent the array, map, nested field without forcing a fixed schema. It is very flexible, but the flexibility comes with a cost - filtering on JSON string columns is very expensive.
Suppose we have some JSON records similar to the following sample record stored in the person
column:
Without an index, in order to look up a key and filter records based on the value, we need to scan and reconstruct the JSON object from the JSON string for every record, look up the key and then compare the value.
For example, in order to find all persons whose name is "adam", the query will look like:
JSON index is designed to accelerate the filtering on JSON string columns without scanning and reconstructing all the JSON objects.
To enable the JSON index, set the following config in the table config:
0.12.0
:maxLevels
Max levels to flatten the json object (array is also counted as one level)
int
-1 (unlimited)
excludeArray
Whether to exclude array when flattening the object
boolean
false (include array)
disableCrossArrayUnnest
Whether to not unnest multiple arrays (unique combination of all elements)
boolean
false (calculate unique combination of all elements)
includePaths
Only include the given paths, e.g. "$.a.b", "$.a.c[*]" (mutual exclusive with excludePaths). Paths under the included paths will be included, e.g. "$.a.b.c" will be included when "$.a.b" is configured to be included.
Set<String>
null (include all paths)
excludePaths
Exclude the given paths, e.g. "$.a.b", "$.a.c[*]" (mutual exclusive with includePaths). Paths under the excluded paths will also be excluded, e.g. "$.a.b.c" will be excluded when "$.a.b" is configured to be excluded.
Set<String>
null (include all paths)
excludeFields
Exclude the given fields, e.g. "b", "c", even if it is under the included paths.
Set<String>
null (include all fields)
With the following JSON document:
With the default setting, we will flatten the document into the following records:
With maxLevels set to 1:
With maxLevels set to 2:
With excludeArray set to true:
With disableCrossArrayUnnest set to true:
With includePaths set to ["$.name", "$.addresses[*].country"]:
With excludePaths set to ["$.age", "$.addresses[*].number"]:
With excludeFields set to ["age", "street"]:
0.12.0
:The legacy config has the same behavior as the default settings in the new config.
Note that JSON index can only be applied to STRING/JSON
columns whose values are JSON strings.
When you're using a JSON index, we would recommend that you add the indexed column to the noDictionaryColumns
columns list to reduce unnecessary storage overhead.
For instructions on that config property, see the Raw value forward index documentation.
JSON index can be used via the JSON_MATCH
predicate: JSON_MATCH(<column>, '<filterExpression>')
. For example, to find all persons whose name is "adam", the query will look like:
Note that the quotes within the filter expression need to be escaped.
In release 0.7.1
, we use the old syntax for filterExpression
: 'name=''adam'''
Find all persons whose name is "adam":
In release 0.7.1
, we use the old syntax for filterExpression: 'name=''adam'''
Find all persons who have an address (one of the addresses) with number 112:
In release 0.7.1
, we use the old syntax for filterExpression: 'addresses.number=112'
Find all persons whose name is "adam" and also have an address (one of the addresses) with number 112:
In release 0.7.1
, we use the old syntax for filterExpression: 'name=''adam'' AND addresses.number=112'
Find all persons whose first address has number 112:
In release 0.7.1
, we use the old syntax for filterExpression: '"addresses[0].number"=112'
Find all persons who have a phone field within the JSON:
In release 0.7.1
, we use the old syntax for filterExpression: 'phone IS NOT NULL'
Find all persons whose first address does not contain floor field within the JSON:
In release 0.7.1
, we use the old syntax for filterExpression: '"addresses[0].floor" IS NULL'
The JSON context is maintained for object elements within an array, i.e. the filter won't cross-match different objects in the array.
To find all persons who live on "main st" in "ca":
This query won't match "adam" because none of his addresses matches both the street and the country.
If JSON context is not desired, use multiple separate JSON_MATCH
predicates. E.g. to find all persons who have addresses on "main st" and have addressed in "ca" (doesn't have to be the same address):
This query will match "adam" because one of his addresses matches the street and another one matches the country.
Note that the array index is maintained as a separate entry within the element, so in order to query different elements within an array, multiple JSON_MATCH
predicates are required. E.g. to find all persons who have first address on "main st" and second address on "second st":
See examples above.
To find the records with array element "item1" in "arrayCol":
To find the records with second array element "item2" in "arrayCol":
To find the records with value 123 in "valueCol":
To find the records with null in "nullableCol":
In release 0.7.1
, json string must be object (cannot be null
, value or array); multi-dimensional array is not supported.
The key (left-hand side) of the filter expression must be the leaf level of the JSON object, e.g. "$.addresses[*]"='main st'
won't work.