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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" |
Last modified 1yr ago