Querying JSON data
To see how JSON data can be queried, assume that we have the following table:
Table myTable:
id INTEGER
jsoncolumn JSON
Table data:
101,{"name":{"first":"daffy"\,"last":"duck"}\,"score":101\,"data":["a"\,"b"\,"c"\,"d"]}
102,{"name":{"first":"donald"\,"last":"duck"}\,"score":102\,"data":["a"\,"b"\,"e"\,"f"]}
103,{"name":{"first":"mickey"\,"last":"mouse"}\,"score":103\,"data":["a"\,"b"\,"g"\,"h"]}
104,{"name":{"first":"minnie"\,"last":"mouse"}\,"score":104\,"data":["a"\,"b"\,"i"\,"j"]}
105,{"name":{"first":"goofy"\,"last":"dwag"}\,"score":104\,"data":["a"\,"b"\,"i"\,"j"]}
106,{"person":{"name":"daffy duck"\,"companies":[{"name":"n1"\,"title":"t1"}\,{"name":"n2"\,"title":"t2"}]}}
107,{"person":{"name":"scrooge mcduck"\,"companies":[{"name":"n1"\,"title":"t1"}\,{"name":"n2"\,"title":"t2"}]}}
We also assume that "jsoncolumn" has a Json Index on it. Note that the last two rows in the table have different structure than the rest of the rows. In keeping with JSON specification, a JSON column can contain any valid JSON data and doesn't need to adhere to a predefined schema. To pull out the entire JSON document for each row, we can run the query below:
SELECT id, jsoncolumn
FROM myTable
id
jsoncolumn
"101"
"{"name":{"first":"daffy","last":"duck"},"score":101,"data":["a","b","c","d"]}"
102"
"{"name":{"first":"donald","last":"duck"},"score":102,"data":["a","b","e","f"]}
"103"
"{"name":{"first":"mickey","last":"mouse"},"score":103,"data":["a","b","g","h"]}
"104"
"{"name":{"first":"minnie","last":"mouse"},"score":104,"data":["a","b","i","j"]}"
"105"
"{"name":{"first":"goofy","last":"dwag"},"score":104,"data":["a","b","i","j"]}"
"106"
"{"person":{"name":"daffy duck","companies":[{"name":"n1","title":"t1"},{"name":"n2","title":"t2"}]}}"
"107"
"{"person":{"name":"scrooge mcduck","companies":[{"name":"n1","title":"t1"},{"name":"n2","title":"t2"}]}}"
To drill down and pull out specific keys within the JSON column, we simply append the JsonPath expression of those keys to the end of the column name.
SELECT id,
json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null') last_name,
json_extract_scalar(jsoncolumn, '$.name.first', 'STRING', 'null') first_name
json_extract_scalar(jsoncolumn, '$.data[1]', 'STRING', 'null') value
FROM myTable
id
last_name
first_name
value
101
duck
daffy
b
102
duck
donald
b
103
mouse
mickey
b
104
mouse
minnie
b
105
dwag
goofy
b
106
null
null
null
107
null
null
null
Note that the third column (value) is null for rows with id 106 and 107. This is because these rows have JSON documents that don't have a key with JsonPath $.data[1]. We can filter out these rows.
SELECT id,
json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null') last_name,
json_extract_scalar(jsoncolumn, '$.name.first', 'STRING', 'null') first_name,
json_extract_scalar(jsoncolumn, '$.data[1]', 'STRING', 'null') value
FROM myTable
WHERE JSON_MATCH(jsoncolumn, '"$.data[1]" IS NOT NULL')
id
last_name
first_name
value
101
duck
daffy
b
102
duck
donald
b
103
mouse
mickey
b
104
mouse
minnie
b
105
dwag
goofy
b
Certain last names (duck and mouse for example) repeat in the data above. We can get a count of each last name by running a GROUP BY query on a JsonPath expression.
SELECT json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null') last_name,
count(*)
FROM myTable
WHERE JSON_MATCH(jsoncolumn, '"$.data[1]" IS NOT NULL')
GROUP BY json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null')
ORDER BY 2 DESC
jsoncolumn.name.last
count(*)
"mouse"
"2"
"duck"
"2"
"dwag"
"1"
Also there is numerical information (jsconcolumn.$.id) embeded within the JSON document. We can extract those numerical values from JSON data into SQL and sum them up using the query below.
SELECT json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null') last_name,
sum(json_extract_scalar(jsoncolumn, '$.id', 'INT', 0)) total
FROM myTable
WHERE JSON_MATCH(jsoncolumn, '"$.name.last" IS NOT NULL')
GROUP BY json_extract_scalar(jsoncolumn, '$.name.last', 'STRING', 'null')
jsoncolumn.name.last
sum(jsoncolumn.score)
"mouse"
"207"
"dwag"
"104"
"duck"
"203"
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