oracle - 管道破裂迭代？

Question

我有一个非常奇怪的问题，我希望你的眼睛能帮助解决它。

我定义了一个函数，它通过 BASH 连接到 Oracle SQL 数据库。连接后，我使用 HEREDOC传递一个简单的 select 语句，该语句查找最大订阅 id 并根据该函数被调用的次数递增它。这是代码:

    #!/bin/bash
    PASS=0
    function NewUserSubID(){
    PASS=$(($PASS+1))
    sqlplus "${DB_USER}"/"${DB_PASS}" <<EOF
    set echo on timing on lines 200 pages 100
    select max(SUBSCRIPTION_ID)+${PASS} from ${DB_ENV}.USER_DATA;
    EOF
    }

当在命令行调用该函数时，上面的代码效果很好:

[root@localhost]> NewUserSubID
SQL*Plus: Release 11.2 Production
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2

SQL> SQL> 
MAX(SUBSCRIPTION_ID)+1
-------------------------------------
                                 1082
Elapsed: 00:00:00.00
SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2


[root@localhost]> NewUserSubID
SQL*Plus: Release 11.2 Production
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2

SQL> SQL> 
MAX(SUBSCRIPTION_ID)+2
-------------------------------------
                                 1083
Elapsed: 00:00:00.00
SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2


[root@localhost]> NewUserSubID
SQL*Plus: Release 11.2 Production
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2

SQL> SQL> 
MAX(SUBSCRIPTION_ID)+3
-------------------------------------
                                 1084
Elapsed: 00:00:00.00
SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2


[root@localhost]> NewUserSubID
SQL*Plus: Release 11.2 Production
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2

SQL> SQL> 
MAX(SUBSCRIPTION_ID)+4
-------------------------------------
                                 1085
Elapsed: 00:00:00.00
SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2

但是，当函数通过管道传输到 AWK 语句中时，函数不再迭代，这是没有意义的!请参阅下面的输出:

[root@localhost] > NewUserSubID | awk 'NR==9{print $1}'
1086
[root@localhost] > NewUserSubID | awk 'NR==9{print $1}'
1086
[root@localhost] > NewUserSubID | awk 'NR==9{print $1}'
1086
[root@localhost] > NewUserSubID | awk 'NR==9{print $1}'
1086
[root@localhost] > NewUserSubID | awk 'NR==9{print $1}'
1086

我不明白。哈哈，我真的希望我只是忽略了一些简单的事情，但我没有想法。任何帮助都会很棒!

Answer 1

问题是管道用作此处命令的一部分:

NewUserSubID | awk 'NR==9{print $1}'

由于管道创建了一个子 shell，因此子 shell 中任何变量所做的更改都不会反射(reflect)在父 shell 中。

您可以使用进程替换来避免使用子 shell:

$> NewUserSubID> >(awk 'NR==9{print $1}')
1086

$> NewUserSubID> >(awk 'NR==9{print $1}')
1087

$> NewUserSubID> >(awk 'NR==9{print $1}')
1088