Question

初学SQL问题。假设我有两张桌子

表1

ID name1 name2 name3
-- ----- ----- -----
1  blah1  high south
2  blah2  low  north  
3  blah3  high north
4  blah4  low  south

表2

ID head1 head2
-- ----- ----------
1  blah5  super high south
2  blah6  medium high northern
3  blah7  kind of low north
4  blah8  kind of low south

现在我想将table2的记录添加到table1。但列name2和name3的数据合并在head2 table1的字符串中。所以我想从head2' and put them in table1'中提取这些字段，使它看起来像这样

表1

ID name1 name2 name3  
-- ----- ----- -----
1  blah1  high south
2  blah2  low  north 
3  blah3  high north 
4  blah4  low  south
5  blah5  high south
6  blah6  high north
7  blah7  low  north 
8  blah8  low  south

现在我想到了某种IF语句（但不知道如何在SQL中实现它）

for each record in table2 do
    table1.name1.insert(head1)
    if table2.head2 == "super high south" then
        table1.name2.insert(high)
        table1.name3.insert(south)
    if table2.head2 == "medium high northern" then
        table1.name2.insert(high)
        table1.name3.insert(north)  

    etc....

在我的实际应用程序中，head2中的唯一字符串类型数量有限，因此每个字符串的if语句都是可行的

您如何编写SQL查询（对于Microsoft Access）来执行此操作？

Answer 1

使用有限数量的[head2]值，您可以使用Switch()函数编写“if语句”逻辑，如下所示：

INSERT INTO table1 (name1, name2, name3)
SELECT
    head1 AS name1,
    Switch(
        head2="super high south", "high",
        head2="medium high northern", "high",
        head2="kind of low north", "low",
        head2="kind of low south", "low")
        AS name2,
    Switch(
        head2="super high south", "south",
        head2="medium high northern", "north",
        head2="kind of low north", "north",
        head2="kind of low south", "south")
        AS name3
FROM table2

在SQL中合并表和修改字符串记录（Microsoft访问）

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