# 去重

下列函数中，有一个实现了合并两个 jsonb 对象并对其去重，是哪一项？

## 答案

```postgresql
create function jsonb_distinct_merge(a jsonb, b jsonb) returns jsonb as
$$
    select jsonb_agg(distinct (value)) from jsonb_array_elements(a || b)
$$ language sql
```

## 选项

### A

```postgresql
create function jsonb_distinct_merge(a jsonb, b jsonb) returns jsonb as $$
    select a || b
$$ language sql
```

### B

```postgresql
create function jsonb_distinct_merge(a jsonb, b jsonb) returns jsonb as $$
return jsonb_agg(distinct(value)) from jsonb_array_elements(a||b)
$$ language sql
```

### C

```postgresql
create function jsonb_distinct_merge(a jsonb, b jsonb) returns jsonb as $$
    return next jsonb_agg(distinct(value)) from jsonb_array_elements(a||b)
$$ language sql
```

### D

```postgresql
create function jsonb_distinct_merge(a jsonb, b jsonb) returns jsonb as $$
    select a + b;
$$ language sql
```