mysql - 单表和多表语法的区别？

Question

我想了解MYSQL 是如何确定单表和多表语法的，但我找不到这些信息。 documentation解释了 MYSQL 如何处理这两者，但没有解释是什么决定了它们。

文档说:

You can specify multiple tables in a DELETE statement to delete rows from one or more tables depending on the particular condition in the WHERE clause. However, you cannot use ORDER BY or LIMIT in a multiple-table DELETE.

以这个查询为例:

DELETE table FROM table
INNER JOIN other ON other.column = table.column
WHERE other.column2 = ?
LIMIT 1

这是单表语法还是多表语法？有一个 JOIN，因此您可以倾向于多个，但它只是从一个表中删除。我的另一个怀疑是，它是在多个 WHERE 子句用于多个表时确定的。如果您能在回答中包含这两个示例，我们将不胜感激!

编辑:
我问这个问题是因为当使用 LIMIT 执行某些 DELETE 查询时，我得到一个错误，您不能将 LIMIT 与多表语法一起使用.

编辑#2: 简而言之，如果要在 DELETE 查询中联接表，则不能使用 ORDER BY 或 LIMIT。

Answer 1

MySQL's documentation states the following

关于“单表”语法:

If the ORDER BY clause is specified, the rows are deleted in the order that is specified. The LIMIT clause places a limit on the number of rows that can be deleted.

关于“多表”语法:

For the multiple-table syntax, DELETE deletes from each tbl_name the rows that satisfy the conditions. In this case, ORDER BY and LIMIT cannot be used.

---

一些测试揭示了 ORDER BY 的局限性。

这是一个有效的单表 DELETE 语句，带有 ORDER BY:

DELETE FROM table
WHERE somecol = 'someval'
ORDER BY timestamp LIMIT 2

对另一个表进行显式连接条件的类似查询会导致 ORDER BY 语法错误，尽管只有一个表被删除:

DELETE table1 
FROM table1 JOIN table2 ON table1.id = table2.id
WHERE somecol = 'someval'
ORDER BY timestamp LIMIT 2

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ORDER BY timestamp LIMIT 2' at line 1

用隐式连接指定相同的查询以同样的方式失败

DELETE table1 
FROM table1, table2
WHERE
  table1.id = table2.id
  AND somecol = 'someval'
ORDER BY timestamp LIMIT 2

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ORDER BY timestamp LIMIT 2' at line 1

在连接(多表)语句中，在 DELETE 之后没有指定表用于删除，因此它看起来更像是单表语法也是语法错误

DELETE /* no table named here */
FROM table1 JOIN table2 ON table1.id = table2.id
WHERE somecol = 'someval'
ORDER BY timestamp LIMIT 2

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'WHERE somecol

它是在DELETE 子句中命名的表:

最后，只使用一个表，但使用多表语法(在 DELETE 关键字后命名表)不允许 ORDER BY，所以这里真正的识别区别似乎是在 DELETE 子句中命名的表，以区分多表和单表:

此查询仅涉及一个表(没有连接)，但会产生语法错误:

/* name table1 in the DELETE clause */
DELETE table1
/* but not other table is joined */
FROM table1
WHERE somecol = 'someval'
ORDER BY id LIMIT 2

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ORDER BY id LIMIT 1