postgresql 使用 exec 而不是 select 调用函数
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Calling functions with exec instead of select
提问by Diego
Is the default way of calling a function select * from my_function()?
是调用函数的默认方式select * from my_function()吗？
I ask because I have built a function that doesn't return anything, just inserts data into a table and (coming from a SQL Server background) it "feels" strange to call it with select * from...
我问是因为我构建了一个不返回任何内容的函数，只是将数据插入表中，并且（来自 SQL Server 背景）调用它“感觉”很奇怪 select * from...
I was expecting something like exec my_function()
我期待着类似的东西 exec my_function()
回答by Roman Pekar
use PERFORMstatement - http://www.postgresql.org/docs/current/static/plpgsql-statements.html
使用PERFORM语句 - http://www.postgresql.org/docs/current/static/plpgsql-statements.html
Sometimes it is useful to evaluate an expression or SELECT query but discard the result, for example when calling a function that has side-effects but no useful result value. To do this in PL/pgSQL, use the PERFORM statement
有时，评估表达式或 SELECT 查询但丢弃结果很有用，例如在调用具有副作用但没有有用结果值的函数时。要在 PL/pgSQL 中执行此操作，请使用 PERFORM 语句
so it's just
所以这只是
DO $$ BEGIN
PERFORM my_function();
END $$;
回答by Craig Ringer
PostgreSQL 11:
PostgreSQL 11：
PostgreSQL 11 supports true stored proceduresas pointed out by @AbdisamadKhalif . They support in-procedure transaction control.
正如@AbdisamadKhalif 所指出的那样，PostgreSQL 11支持真正的存储过程。它们支持过程中事务控制。
Older versions:
旧版本：
Yes, that's the standard way, and yes it's weird.
是的，这是标准方式，是的，这很奇怪。
Usually you'd write such functions as stored proceduresand invoke them with the CALLor EXECUTEcommand. PostgreSQL does not support true stored procedures (multiple result sets, autonomous transactions, and all that) though, only sql-callable user-defined functions.
通常您会编写诸如存储过程之类的函数并使用CALLorEXECUTE命令调用它们。PostgreSQL 不支持真正的存储过程（多个结果集、自治事务等），但只支持sql 可调用的用户定义函数。
So the workaround is to SELECT function_name()using the PostgreSQL extension syntax that omits FROM, or SELECT 1 FROM function_name();to be (somewhat) more standard.
因此，解决方法是SELECT function_name()使用省略 的 PostgreSQL 扩展语法FROM，或者SELECT 1 FROM function_name();（有点）更标准。
The ODBC driver, JDBC driver, etc understand the {call func_name()}escape syntax and automatically translate it to an underlying SELECT.
ODBC 驱动程序、JDBC 驱动程序等理解{call func_name()}转义语法并自动将其转换为底层SELECT.
回答by Clodoaldo Neto
You will use fromwhen the function returns a set. If the function returns voidjust do
from当函数返回一个集合时，您将使用。如果函数返回void就做
select my_function();
