我想知道这在SQL中是否可行.假设您有两个表A和B,并在表A上执行选择并在表B上进行连接:
SELECT a.*, b.* FROM TABLE_A a JOIN TABLE_B b USING (some_id);
如果表A包含列'a_id','name'和'some_id',而表B包含'b_id','name'和'some_id',则查询将返回列'a_id','name','some_id ','b_id','name','some_id'.有没有办法为表B的列名添加前缀而不单独列出每一列？相当于:
SELECT a.*, b.b_id as 'b.b_id', b.name as 'b.name', b.some_id as 'b.some_id'
FROM TABLE_A a JOIN TABLE_B b USING (some_id);
但是,如上所述,没有列出每一列,所以类似于:
SELECT a.*, b.* as 'b.*'
FROM TABLE_A a JOIN TABLE_B b USING (some_id);
基本上可以说,"b.*返回的每一列都带有'某事'".这可能还是我运气不好？
在此先感谢您的帮助!
编辑:不使用SELECT*等建议是有效的建议,但在我的上下文中不相关,所以请坚持手头的问题 - 是否可以添加前缀(SQL查询中指定的常量)给所有连接中表的列名？
编辑:我的最终目标是能够在两个带连接的表上执行SELECT*,并且能够从我在结果集中获得的列的名称中说明哪些列来自表A以及哪些列来自哪些列从表B.再次,我不想单独列出列,我需要能够做一个SELECT*.
小智 66
似乎你的问题的答案是否定的,但是你可以使用的一个黑客是分配一个虚拟列来分隔每个新表.如果您在脚本语言(如Python或PHP)中循环遍历列的结果集,则此方法尤其有用.
SELECT '' as table1_dummy, table1.*, '' as table2_dummy, table2.*, '' as table3_dummy, table3.* FROM table1
JOIN table2 ON table2.table1id = table1.id
JOIN table3 ON table3.table1id = table1.id
我意识到这并不能完全回答你的问题,但如果你是一个编码器,这是一个很好的方法来分隔具有重复列名的表.希望这有助于某人.
dkr*_*etz 34
我在这看到两种可能的情况.首先,您想知道是否存在针对此的SQL标准,无论数据库如何,您都可以使用该标准.不,那里没有.其次,您想了解特定的dbms产品.然后你需要识别它.但我想最可能的答案是你会得到像"a.id,b.id"这样的东西,因为这就是你需要在SQL表达式中识别列的方法.找出默认设置的最简单方法就是提交这样的查询,看看你得到了什么.如果要在点之前指定前缀,可以使用"SELECT*FROM AS my_alias".
Mot*_*tin 22
我完全理解为什么这是必要的 - 至少对我而言,在快速原型制作过程中,当需要加入很多表时,包括许多内部连接时,它很方便.只要第二个"joinedtable.*"字段通配符中的列名相同,主表的字段值将使用jointable值覆盖.当必须手动指定带有别名的表字段时,容易出错,令人沮丧并且违反DRY ......
这是一个PHP(Wordpress)函数,通过代码生成以及如何使用它的示例实现此目的.在该示例中,它用于快速生成自定义查询,该查询将提供通过高级自定义字段字段引用的相关wordpress帖子的字段.
function prefixed_table_fields_wildcard($table, $alias)
{
global $wpdb;
$columns = $wpdb->get_results("SHOW COLUMNS FROM $table", ARRAY_A);
$field_names = array();
foreach ($columns as $column)
{
$field_names[] = $column["Field"];
}
$prefixed = array();
foreach ($field_names as $field_name)
{
$prefixed[] = "`{$alias}`.`{$field_name}` AS `{$alias}.{$field_name}`";
}
return implode(", ", $prefixed);
}
function test_prefixed_table_fields_wildcard()
{
global $wpdb;
$query = "
SELECT
" . prefixed_table_fields_wildcard($wpdb->posts, 'campaigns') . ",
" . prefixed_table_fields_wildcard($wpdb->posts, 'venues') . "
FROM $wpdb->posts AS campaigns
LEFT JOIN $wpdb->postmeta meta1 ON (meta1.meta_key = 'venue' AND campaigns.ID = meta1.post_id)
LEFT JOIN $wpdb->posts venues ON (venues.post_status = 'publish' AND venues.post_type = 'venue' AND venues.ID = meta1.meta_value)
WHERE 1
AND campaigns.post_status = 'publish'
AND campaigns.post_type = 'campaign'
LIMIT 1
";
echo "<pre>$query</pre>";
$posts = $wpdb->get_results($query, OBJECT);
echo "<pre>";
print_r($posts);
echo "</pre>";
}
输出:
SELECT
`campaigns`.`ID` AS `campaigns.ID`, `campaigns`.`post_author` AS `campaigns.post_author`, `campaigns`.`post_date` AS `campaigns.post_date`, `campaigns`.`post_date_gmt` AS `campaigns.post_date_gmt`, `campaigns`.`post_content` AS `campaigns.post_content`, `campaigns`.`post_title` AS `campaigns.post_title`, `campaigns`.`post_excerpt` AS `campaigns.post_excerpt`, `campaigns`.`post_status` AS `campaigns.post_status`, `campaigns`.`comment_status` AS `campaigns.comment_status`, `campaigns`.`ping_status` AS `campaigns.ping_status`, `campaigns`.`post_password` AS `campaigns.post_password`, `campaigns`.`post_name` AS `campaigns.post_name`, `campaigns`.`to_ping` AS `campaigns.to_ping`, `campaigns`.`pinged` AS `campaigns.pinged`, `campaigns`.`post_modified` AS `campaigns.post_modified`, `campaigns`.`post_modified_gmt` AS `campaigns.post_modified_gmt`, `campaigns`.`post_content_filtered` AS `campaigns.post_content_filtered`, `campaigns`.`post_parent` AS `campaigns.post_parent`, `campaigns`.`guid` AS `campaigns.guid`, `campaigns`.`menu_order` AS `campaigns.menu_order`, `campaigns`.`post_type` AS `campaigns.post_type`, `campaigns`.`post_mime_type` AS `campaigns.post_mime_type`, `campaigns`.`comment_count` AS `campaigns.comment_count`,
`venues`.`ID` AS `venues.ID`, `venues`.`post_author` AS `venues.post_author`, `venues`.`post_date` AS `venues.post_date`, `venues`.`post_date_gmt` AS `venues.post_date_gmt`, `venues`.`post_content` AS `venues.post_content`, `venues`.`post_title` AS `venues.post_title`, `venues`.`post_excerpt` AS `venues.post_excerpt`, `venues`.`post_status` AS `venues.post_status`, `venues`.`comment_status` AS `venues.comment_status`, `venues`.`ping_status` AS `venues.ping_status`, `venues`.`post_password` AS `venues.post_password`, `venues`.`post_name` AS `venues.post_name`, `venues`.`to_ping` AS `venues.to_ping`, `venues`.`pinged` AS `venues.pinged`, `venues`.`post_modified` AS `venues.post_modified`, `venues`.`post_modified_gmt` AS `venues.post_modified_gmt`, `venues`.`post_content_filtered` AS `venues.post_content_filtered`, `venues`.`post_parent` AS `venues.post_parent`, `venues`.`guid` AS `venues.guid`, `venues`.`menu_order` AS `venues.menu_order`, `venues`.`post_type` AS `venues.post_type`, `venues`.`post_mime_type` AS `venues.post_mime_type`, `venues`.`comment_count` AS `venues.comment_count`
FROM wp_posts AS campaigns
LEFT JOIN wp_postmeta meta1 ON (meta1.meta_key = 'venue' AND campaigns.ID = meta1.post_id)
LEFT JOIN wp_posts venues ON (venues.post_status = 'publish' AND venues.post_type = 'venue' AND venues.ID = meta1.meta_value)
WHERE 1
AND campaigns.post_status = 'publish'
AND campaigns.post_type = 'campaign'
LIMIT 1
Array
(
[0] => stdClass Object
(
[campaigns.ID] => 33
[campaigns.post_author] => 2
[campaigns.post_date] => 2012-01-16 19:19:10
[campaigns.post_date_gmt] => 2012-01-16 19:19:10
[campaigns.post_content] => Lorem ipsum
[campaigns.post_title] => Lorem ipsum
[campaigns.post_excerpt] =>
[campaigns.post_status] => publish
[campaigns.comment_status] => closed
[campaigns.ping_status] => closed
[campaigns.post_password] =>
[campaigns.post_name] => lorem-ipsum
[campaigns.to_ping] =>
[campaigns.pinged] =>
[campaigns.post_modified] => 2012-01-16 21:01:55
[campaigns.post_modified_gmt] => 2012-01-16 21:01:55
[campaigns.post_content_filtered] =>
[campaigns.post_parent] => 0
[campaigns.guid] => http://example.com/?p=33
[campaigns.menu_order] => 0
[campaigns.post_type] => campaign
[campaigns.post_mime_type] =>
[campaigns.comment_count] => 0
[venues.ID] => 84
[venues.post_author] => 2
[venues.post_date] => 2012-01-16 20:12:05
[venues.post_date_gmt] => 2012-01-16 20:12:05
[venues.post_content] => Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
[venues.post_title] => Lorem ipsum venue
[venues.post_excerpt] =>
[venues.post_status] => publish
[venues.comment_status] => closed
[venues.ping_status] => closed
[venues.post_password] =>
[venues.post_name] => lorem-ipsum-venue
[venues.to_ping] =>
[venues.pinged] =>
[venues.post_modified] => 2012-01-16 20:53:37
[venues.post_modified_gmt] => 2012-01-16 20:53:37
[venues.post_content_filtered] =>
[venues.post_parent] => 0
[venues.guid] => http://example.com/?p=84
[venues.menu_order] => 0
[venues.post_type] => venue
[venues.post_mime_type] =>
[venues.comment_count] => 0
)
)
Joe*_*ove 17
在 postgres 中，我使用 json 函数来返回 json 对象......然后，在查询后，我对带有 _json 后缀的字段进行 json_decode。
IE：
select row_to_json(tab1.*) AS tab1_json, row_to_json(tab2.*) AS tab2_json
from tab1
join tab2 on tab2.t1id=tab1.id
然后在 PHP（或任何其他语言）中，我循环遍历返回的列，如果它们具有“_json”后缀（也删除后缀），则对它们进行 json_decode() 。最后，我得到一个名为“tab1”的对象，其中包含所有tab1 字段，另一个称为“tab2”，其中包含所有 tab2 字段。
Bil*_*win 12
我知道的唯一数据库是SQLite,具体取决于您配置的设置PRAGMA full_column_names和PRAGMA short_column_names.见http://www.sqlite.org/pragma.html
否则,我建议的是按顺序位置而不是列名来获取结果集中的列,如果在查询中键入列的名称太麻烦了.
这是一个很好的例子,说明为什么使用它是不好的做法SELECT * - 因为最终你需要输入所有的列名.
我理解需要支持可能更改名称或位置的列,但使用通配符会使更难,更容易.
这个问题在实践中非常有用。只需要列出软件编程中的每个显式列，您在处理所有条件时要特别小心。
试想一下，在调试时，或者尝试使用DBMS作为日常办公工具时，我们需要编写大量SQL，而不是特定程序员抽象底层基础设施的一些可变实现。这种场景随处可见，如数据库转换、迁移、管理等。这些 SQL 中的大多数只会执行一次，永远不会再次使用，给每个列名只是浪费时间。并且不要忘记 SQL 的发明并不仅仅供程序员使用。
通常我会创建一个带有列名前缀的实用程序视图，这里是 pl/pgsql 中的函数，这并不容易，但您可以将其转换为其他过程语言。
-- Create alias-view for specific table.
create or replace function mkaview(schema varchar, tab varchar, prefix varchar)
returns table(orig varchar, alias varchar) as $$
declare
qtab varchar;
qview varchar;
qcol varchar;
qacol varchar;
v record;
sql varchar;
len int;
begin
qtab := '"' || schema || '"."' || tab || '"';
qview := '"' || schema || '"."av' || prefix || tab || '"';
sql := 'create view ' || qview || ' as select';
for v in select * from information_schema.columns
where table_schema = schema and table_name = tab
loop
qcol := '"' || v.column_name || '"';
qacol := '"' || prefix || v.column_name || '"';
sql := sql || ' ' || qcol || ' as ' || qacol;
sql := sql || ', ';
return query select qcol::varchar, qacol::varchar;
end loop;
len := length(sql);
sql := left(sql, len - 2); -- trim the trailing ', '.
sql := sql || ' from ' || qtab;
raise info 'Execute SQL: %', sql;
execute sql;
end
$$ language plpgsql;
例子：
-- This will create a view "avp_person" with "p_" prefix to all column names.
select * from mkaview('public', 'person', 'p_');
select * from avp_person;
我使用PostgreSQL 13 中的函数将连接表中的所有字段作为单个列to_jsonb获取。
select
TABLE_A.*,
to_jsonb(TABLE_B.*) as b,
to_jsonb(TABLE_C.*) as c
from TABLE_A
left join TABLE_B on TABLE_B.a_id=TABLE_A.id
left join TABLE_C on TABLE_C.a_id=TABLE_A.id
where TABLE_A.id=1
结果，您将获得 TABLE_A 列的数量加上 b 和 c 列：
| ID | 姓名 | 一些其他列 | 乙 | C |
|---|---|---|---|---|
| 1 | 一些名字 | 其他一些值 | {"id":1,"a_id":1,"prop":"值"} | {"id":1,"a_id":1,"prop":"值"} |
| 1 | 其他一些名字 | 另一个价值 | {"id":1,"a_id":1,"prop":"值"} | {"id":1,"a_id":1,"prop":"值"} |
您只需解析 b 和 c 列即可将它们转换为对象。
小智 6
我与OP的船相同 - 我有3个不同的表中的几十个字段,我正在加入,其中一些具有相同的名称(即id,名称等).我不想列出每个字段,因此我的解决方案是为共享名称的字段添加别名,并对具有唯一名称的字段使用select*.
例如 :
表a:id,name,field1,field2 ......
表b:id,name,field3,field4 ......
选择a.id作为aID,a.name作为aName,a.*,b.id为bID,b.name为bName,b.*.....
访问结果时,我使用这些字段的别名,并忽略"原始"名称.
也许不是最好的解决方案,但它适用于我....我使用的是mysql
不同的数据库产品会给你不同的答案; 但是如果你带着这么远的话,你会让自己受伤.你最好选择你想要的列,并给它们自己的别名,这样每列的标识都是清晰的,你可以在结果中区分它们.
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