mysql left join VALUE

回答: 在MySQL中，您可以使用左连接（LEFT JOIN）来实现左连接值。通过将MAX（WorkDay）条件放入JOIN条件中作为相关的子查询，您可以访问table1的id值，并只获取table2中最新的WorkDay值。这样，您可以获取所有table1字段并左连接table2，但只获取最新的WorkDay值。

相关问题

mysql left join

The LEFT JOIN clause in MySQL is used to combine rows from two or more tables based on a related column between them. The resulting table will contain all the rows from the left table and matching rows from the right table. If there are no matching rows from the right table, then NULL values will be returned.

The syntax for a LEFT JOIN in MySQL is as follows:

SELECT column1, column2, ...
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

In this example, table1 is the left table and table2 is the right table. The ON clause specifies the column that is used to match the rows between the two tables.

For example, consider the following two tables:

Table1:

| id | name | age |
|----|-------|-----|
| 1 | John | 25 |
| 2 | Jane | 30 |
| 3 | David | 35 |

Table2:

| id | city |
|----|----------|
| 1 | New York |
| 2 | London |
| 4 | Paris |

To combine these two tables using a LEFT JOIN on the id column, the following query can be used:

SELECT Table1.name, Table2.city
FROM Table1
LEFT JOIN Table2
ON Table1.id = Table2.id;

The resulting table will be:

| name | city |
|-------|----------|
| John | New York |
| Jane | London |
| David | NULL |

Notice that the row with id=3 from Table1 does not have a corresponding row in Table2, so the city value is NULL in the resulting table.

mysql left join 套数组

可以使用MySQL的IN语句来实现在LEFT JOIN中使用数组。假设你有一个数组，它包含多个值，你想要在LEFT JOIN中使用这些值，你可以像这样编写查询：

SELECT *
FROM table1
LEFT JOIN table2 ON table1.id = table2.table1_id
WHERE table2.column_name IN (value1, value2, value3, ...)

其中，value1、value2、value3等是你想要匹配的值。你可以在IN语句中添加任意多的值。这将返回左表中所有匹配值的行，如果没有匹配值，则右表中的所有列将为NULL。