postgresql Postgres SELECT 多选为
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Postgres SELECT with multiple select as
提问by Matt
I'm trying to use the output from two SELECT statements in a PostGIS function.
我正在尝试在 PostGIS 函数中使用两个 SELECT 语句的输出。
What is the correct syntax for doing this? I'm getting a syntax error at or near the second SELECT statement.
这样做的正确语法是什么？我在第二个 SELECT 语句处或附近遇到语法错误。
SELECT ST_Split(tracks, roads)
FROM
(
SELECT * FROM (SELECT ST_Buffer(road_geom,50) FROM table1 WHERE a = '' AND b = '') as roads,
SELECT * FROM (SELECT the_geom FROM table2 WHERE c = '' AND d = '') as tracks
)
Error output:
错误输出：
ERROR: syntax error at or near "SELECT"
LINE 5: SELECT * FROM (SELECT the_geom FROM table2...
^
********** Error **********
ERROR: syntax error at or near "SELECT"
SQL state: 42601
Character: 178
Thanks!
谢谢！
回答by bma
Demonstrating one method of using a CTE:
演示使用 CTE 的一种方法：
WITH roads as (SELECT ST_Buffer(road_geom,50) as road FROM table1 WHERE a = '' AND b = ''),
tracks as (SELECT the_geom as track FROM table2 WHERE c = '' AND d = '')
SELECT ST_Split( (select track from tracks), (select road from roads) );
Docs at http://www.postgresql.org/docs/current/static/queries-with.html
http://www.postgresql.org/docs/current/static/queries-with.html 上的文档
