I have a list ob objects. Each object contains several properties. Now I want to make a SELECT statement that gives me a list of a single property values. The simplified list look like this:
[
[
{
"day": "2021-10-01",
"entries": [
{
"name": "Start of competition",
"startTimeDelta": "08:30:00"
}
]
},
{
"day": "2021-10-02",
"entries": [
{
"name": "Start of competition",
"startTimeDelta": "03:30:00"
}
]
},
{
"day": "2021-10-03",
"entries": [
{
"name": "Start of competition"
}
]
}
]
]
The working SELECT is now
SELECT
JSON_EXTRACT(column, '$.days[*].entries[0].startTimeDelta') AS list
FROM table
The returned result is
[
"08:30:00",
"03:30:00"
]
But what I want to get (and also have expected) is
[
"08:30:00",
"03:30:00",
null
]
What can I do or how can I change the SELECT statement so that I also get NULL values in the list?
CodePudding user response：
SELECT startTimeDelta
FROM test
CROSS JOIN JSON_TABLE(val,
'$[*][*].entries[*]' COLUMNS (startTimeDelta TIME PATH '$.startTimeDelta')) jsontable
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=491f0f978d200a8a8522e3200509460e
Do you also have a working idea for MySQL< 8? – Lars
What is max amount of objects in the array on the 2nd level? – Akina
Well it's usually less than 10 – Lars
SELECT JSON_EXTRACT(val, CONCAT('$[0][', num, '].entries[0].startTimeDelta')) startTimeDelta
FROM test
-- up to 4 - increase if needed
CROSS JOIN (SELECT 0 num UNION SELECT 1 UNION SELECT 2 UNION SELECT 3) nums
WHERE JSON_EXTRACT(val, CONCAT('$[0][', num, '].entries[0]')) IS NOT NULL;