PostgreSQL：SQL 中的硬编码字符串

Question

如何在 PostgreSQL SELECT 中有硬编码字符串？

就像是：

SELECT
 'some value' As FieldName
 FROM table

上面给出了 pgAdmin 中的错误。

Answer 1

Craig Ringers 的回答（一如既往）是正确的，我想为其添加以下扩展名：

--
-- This is how you can define a hardcoded value as column (here as the type 'text').
-- Instead of the explicit 'CAST(...)' call it's also possible to use the
-- '::text' short version.
--
-- NOTE-1: The short version or omitting the type completely might not
--         work in every SQL client (e. g. SquirrelSQL), while the
--         CAST(...) call is pretty safe.
--
-- NOTE-2: Please always use lower case column names!
--
SELECT CAST('some value' AS text) AS fieldname;

Answer 2

在 SELECT 关键字之后只能插入列名。也许你正在寻找这样的东西

SELECT 'columnname' AS 'alias'
FROM 'tablename'
WHERE 'alias/columnname' = 'hardcodedvalue';