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docs: improved en version of sql/dql/group_by #2241

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docs: improved en version of sql/dql/group_by #2241

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20 changes: 8 additions & 12 deletions docs/en/reference/sql/dql/GROUP_BY_CLAUSE.md
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# GROUP BY Clause

All -group by- currently only has supports in batch mode (that is, console debugging SQL support, offline mode is still under development)

## Syntax

```SQL
Expand All @@ -17,25 +15,23 @@ SELECT select_expr [,select_expr...] FROM ... GROUP BY ...

## Boundary Description
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| SELECT statement elements | state | directions |
| :-------------- | ------------- | :----------------------------------------------------------- |
| GROUP BY Clause | Online not supported | Group By clause is used to group the query result set. Grouping expression lists only support simple columns. |

For the standalone version, `GROUP BY` is supported in all conditions. For the cluster version, the execution modes which support this clause are shown below.

| `SELECT` Statement Elements | Offline Mode | Online Preview Mode | Online Request Mode | Note |
|:-----------------------------------------------------------|--------------|---------------------|---------------------|:------------------------------------------------------------------------------------------------------------------------|
| GROUP BY Clause | **``✓``** | | | The Group By clause is used to group the query results.The grouping conditions only support grouping on simple columns. |

## Example

### 1. Aggregate After Grouping By Column
**1. Aggregate After Grouping By One Column**

```SQL
-- desc: simple SELECT grouping KEY
SELECT COL1, SUM(COL2), AVG(COL2) FROM t1 group by COL1;
SELECT COL1, SUM(COL2), AVG(COL2) FROM t1 group by COL1;
```

### 2. Aggregate After Grouping By Two Columns
**2. Aggregate After Grouping By Two Columns**

```SQL
-- desc: simple SELECT grouping KEY
SELECT COL1, SUM(COL2), AVG(COL2) FROM t1 group by COL1, COL0;
SELECT COL1, SUM(COL2), AVG(COL2) FROM t1 group by COL1, COL0;
```