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mysql-compatibility: add doc for a UPDATE incompatibility case (#7781) #9464

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May 13, 2022
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mysql-compatibility: add doc for a UPDATE incompatibility case (#7781) #9464

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6d9b958
mysql-compatibility: add doc for a UPDATE incompatibility case
tiancaiamao Dec 2, 2021
1012768
address comment
tiancaiamao May 11, 2022
577cfd4
Update mysql-compatibility.md
tiancaiamao May 13, 2022
f3051ff
Update sql-statements/sql-statement-update.md
TomShawn May 13, 2022
6a2b9ff
Update sql-statements/sql-statement-update.md
TomShawn May 13, 2022
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4 changes: 4 additions & 0 deletions mysql-compatibility.md
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Expand Up @@ -120,6 +120,10 @@ TiDB 中的[信息统计](/statistics.md#手动收集) 与 MySQL 中的有所不

详情参见 [`SELECT`](/sql-statements/sql-statement-select.md)。

### `UPDATE` 语句

详情参见 [`UPDATE`](/sql-statements/sql-statement-update.md)。

### 视图

TiDB 中的视图不可更新，不支持 `UPDATE`、`INSERT`、`DELETE` 等写入操作。
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12 changes: 11 additions & 1 deletion sql-statements/sql-statement-update.md
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Expand Up @@ -103,7 +103,17 @@ SELECT * FROM t1;

## MySQL 兼容性

`UPDATE` 语句与 MySQL 完全兼容。如发现任何兼容性差异，请在 GitHub 上提交 [issue](https://github.com/pingcap/tidb/issues/new/choose)。
在计算表达式中的列时，TiDB 总使用原始的值。例如：

```sql
CREATE TABLE t (a int, b int);
INSERT INTO t VALUES (1,2);
UPDATE t SET a = a+1,b=a;
```

在 MySQL 中，`b` 列的值会被更新成 2，因为 `b` 列被设置为与 `a` 列相同，而 `a`（最初是 1）在同一条语句中被更新成了 2。

TiDB 遵守标准的 SQL 行为，这里将 `b` 列值更新成 1。

## 另请参阅

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