93 lines
2.6 KiB
Markdown
93 lines
2.6 KiB
Markdown
---
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title: JSON Type
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sidebar_label: JSON Type
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description: This document describes the JSON data type in TDengine.
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---
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## Syntax
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1. Tag of type JSON
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```
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create stable s1 (ts timestamp, v1 int) tags (info json)
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create table s1_1 using s1 tags ('{"k1": "v1"}')
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```
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2. "->" Operator of JSON
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```
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select * from s1 where info->'k1' = 'v1'
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select info->'k1' from s1
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```
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3. "contains" Operator of JSON
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```
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select * from s1 where info contains 'k2'
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select * from s1 where info contains 'k1'
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```
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## Applicable Operations
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1. When a JSON data type is used in `where`, `match/nmatch/between and/like/and/or/is null/is no null` can be used but `in` can't be used.
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```
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select * from s1 where info->'k1' match 'v*';
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select * from s1 where info->'k1' like 'v%' and info contains 'k2';
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select * from s1 where info is null;
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select * from s1 where info->'k1' is not null
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```
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2. A tag of JSON type can be used in `group by`, `order by`, `join`, `union all` and sub query; for example `group by json->'key'`
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3. `Distinct` can be used with a tag of type JSON
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```
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select distinct info->'k1' from s1
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```
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4. Tag Operations
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The value of a JSON tag can be altered. Please note that the full JSON will be overridden when doing this.
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The name of a JSON tag can be altered.
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A tag of JSON type can't be added or removed. The column length of a JSON tag can't be changed.
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## Other Restrictions
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- JSON type can only be used for a tag. There can be only one tag of JSON type, and it's exclusive to any other types of tags.
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- The maximum length of keys in JSON is 256 bytes, and key must be printable ASCII characters. The maximum total length of a JSON is 4,096 bytes.
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- JSON format:
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- The input string for JSON can be empty, i.e. "", "\t", or NULL, but it can't be non-NULL string, bool or array.
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- object can be {}, and the entire JSON is empty if so. Key can be "", and it's ignored if so.
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- value can be int, double, string, bool or NULL, and it can't be an array. Nesting is not allowed which means that the value of a key can't be JSON.
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- If one key occurs twice in JSON, only the first one is valid.
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- Escape characters are not allowed in JSON.
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- NULL is returned when querying a key that doesn't exist in JSON.
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- If a tag of JSON is the result of inner query, it can't be parsed and queried in the outer query.
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For example, the SQL statements below are not supported.
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```
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select jtag->'key' from (select jtag from stable)
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```
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and
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```
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select jtag->'key' from (select jtag from stable) where jtag->'key'>0
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```
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