@Entity
@Table(name = "shift")
public class Shift {

    @EmbeddedId
    private PK pk;

    @Column(insertable = false, updatable = false)
    private LocalDate day;

    @Column(insertable = false, updatable = false)
    private Integer number;

    @Formula("""
    (SELECT json_arrayagg(
      json_object(
        "day", sh.day,
        "number", sh.number,
        "value", sh.value
      )
    )
    FROM shiftData sh WHERE sh.day = day AND sh.number = number)
    """)
    private String data;

    @Embeddable
    public static class PK implements Serializable {

        @Column(name = "day")
        private LocalDate day;

        @Column(name = "number")
        private Integer number;
    }
}

select
        s1_0.day,
        s1_0.number,
        (SELECT
            json_arrayagg(   json_object(     "day", sh.day,     "number", sh.number,     "value", sh.value   ) ) 
        FROM
            shiftData sh 
        WHERE
            sh.day = day 
            AND sh.number = s1_0.number)  
    from
        shift s1_0

        WHERE
            sh.day = day 
            AND sh.number = s1_0.number)

        WHERE
            sh.day = s1_0.day 
            AND sh.number = s1_0.number)