SQL：Select 满足条件的不同项目

Question

I have a relation in a database as follows:

constituents                                                         Symbol
[{"weight":0.5, "ticker":"WPM"},{"weight":0.5, "ticker":"AEM"}]      GLD
[{"weight":0.5, "ticker":"XYZ"},{"weight":0.5, "ticker":"ABC"}]      KLE
[{"weight":1.0, "ticker":"TSLA"}]                                    TSLA
[{"weight":1.0, "ticker":"MSFT"}]                                    MSFT
[{"weight":0.4, "ticker":"XYZ"},{"weight":0.6, "ticker":"ABC"}]      KLE
[{"weight":0.3, "ticker":"BBBY"},{"weight":0.7, "ticker":"GME"}]     MEME

I want to get the distinct symbols where the constituents column contains more than 1 json in the list. So the outcome should be

GLD, KLE, MEME

My attempt is:

SELECT DISTINCT "Symbol" FROM "MyTable" WHERE JSONB_ARRAY_LENGTH("constitutents")>1

but I get an error: ERROR: cannot get array length of a non-array

Answer 1

Just check if it has a comma in it:

SELECT DISTINCT "Symbol" 
FROM "MyTable"
WHERE CONTAINS("constitutents",',')

Answer 2

It depemds how our column is defined as JSON or JSONB, so you need to use the appropriate functions

JSONB

CREATE TABLE T2
    ("constituents" JSONB, "Symbol" varchar(4))
;
    
INSERT INTO T2
    ("constituents", "Symbol")
VALUES
    ('[{"weight":0.5, "ticker":"WPM"},{"weight":0.5, "ticker":"AEM"}]', 'GLD'),
    ('[{"weight":0.5, "ticker":"XYZ"},{"weight":0.5, "ticker":"ABC"}]', 'KLE'),
    ('[{"weight":1.0, "ticker":"TSLA"}]', 'TSLA'),
    ('[{"weight":1.0, "ticker":"MSFT"}]', 'MSFT'),
    ('[{"weight":0.4, "ticker":"XYZ"},{"weight":0.6, "ticker":"ABC"}]', 'KLE'),
    ('[{"weight":0.3, "ticker":"BBBY"},{"weight":0.7, "ticker":"GME"}]', 'MEME')
;

 CREATE TABLE

 INSERT 0 6

SELECT "Symbol" FROM T2 WHERE JSONB_ARRAY_LENGTH("constituents") > 1

Symbol
GLD
KLE
KLE
MEME

SELECT 4

fiddle

Json

CREATE TABLE T2
    ("constituents" JSON, "Symbol" varchar(4))
;
    
INSERT INTO T2
    ("constituents", "Symbol")
VALUES
    ('[{"weight":0.5, "ticker":"WPM"},{"weight":0.5, "ticker":"AEM"}]', 'GLD'),
    ('[{"weight":0.5, "ticker":"XYZ"},{"weight":0.5, "ticker":"ABC"}]', 'KLE'),
    ('[{"weight":1.0, "ticker":"TSLA"}]', 'TSLA'),
    ('[{"weight":1.0, "ticker":"MSFT"}]', 'MSFT'),
    ('[{"weight":0.4, "ticker":"XYZ"},{"weight":0.6, "ticker":"ABC"}]', 'KLE'),
    ('[{"weight":0.3, "ticker":"BBBY"},{"weight":0.7, "ticker":"GME"}]', 'MEME')
;

 CREATE TABLE

 INSERT 0 6

SELECT "Symbol" FROM T2 WHERE JSON_ARRAY_LENGTH("constituents") > 1

Symbol
GLD
KLE
KLE
MEME

SELECT 4

fiddle