当我使用 DBI 的准备/执行非 select 语句时，如何获取受影响的行数？

发布于 2024-11-27 18:54:07 字数 274 浏览 2 评论 0原文

根据 DBI 文档，看来我只能通过 do方法。

$rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");

如果我使用prepare/execute如何才能得到相同的结果？

原文

According to the DBI documentation, it seems I can only get the number of affected rows by the do method.

$rows_affected = $dbh->do("UPDATE your_table SET foo = foo + 1");

How can I get the same result if I use prepare/execute?

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指尖凝香 2024-12-04 18:54:07

从有关 DBI 中的 execute 方法的文档中：

对于非“SELECT”语句，“execute”返回行数
受影响（如果已知）。如果没有行受到影响，则“执行”返回
“0E0”，Perl 将其视为 0，但仍将其视为 true。注意
这是
如果没有行受语句影响，则这不是错误。如果
受影响的行数未知，则“执行”返回 -1。

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木有鱼丸 2024-12-04 18:54:07

如果您的查询是非SELECT查询（例如UPDATE或DELETE），那么您可以利用行：

my $query = "...";  # your query
my $sth = $dbh->prepare($query);
$sth->execute();
print "Number of rows affected: " . $sth->rows . "\n";

行返回受最后一个影响的行数查询或-1 如果出现错误。但是，根据设计，您不能依赖行来执行 SELECT 语句。

请注意，对于非 SELECT 查询，还要执行 返回受影响的行数。但是，如果没有行受到影响，则 execute 返回 "0E0"（Perl 无论如何都应将其视为 0）。

my $query = "...";  # your query
my $sth = $dbh->prepare($query);
my $numrows = $sth->execute();
print "Number of rows affected: " . $numrows . "\n";

相反，如果您的查询是SELECT，那么您就不能依赖行。

但是，您可以执行以下任一操作：

my $query = "SELECT COUNT(*) AS rows FROM ... WHERE ...";
my $numrows = $dbh->selectrow_array($query, undef);
print "Number of rows: " . $numrows . "\n";

或者，类似地：

my $query = "SELECT COUNT(*) AS rows FROM ... WHERE ...";
my $numrows = $dbh->selectall_arrayref($query, { Slice => {} });
print "Number of rows: " . @$numrows[0]->{rows} . "\n";

If your query is a non-SELECT one (e.g. UPDATE or DELETE), then you can take advantage of rows:

my $query = "...";  # your query
my $sth = $dbh->prepare($query);
$sth->execute();
print "Number of rows affected: " . $sth->rows . "\n";

rows returns the number of rows affected by the last query or -1 in case of error. However, by design, you cannot rely on rows for SELECT statement.

Note that, for non-SELECT queries, also execute returns the number of rows affected. However, if no row is affected, then execute returns "0E0" (which Perl should anyway treat as 0).

my $query = "...";  # your query
my $sth = $dbh->prepare($query);
my $numrows = $sth->execute();
print "Number of rows affected: " . $numrows . "\n";

If, instead, your query is a SELECT, then you cannot rely on rows.

However, you can do either:

my $query = "SELECT COUNT(*) AS rows FROM ... WHERE ...";
my $numrows = $dbh->selectrow_array($query, undef);
print "Number of rows: " . $numrows . "\n";

Or, similarly:

my $query = "SELECT COUNT(*) AS rows FROM ... WHERE ...";
my $numrows = $dbh->selectall_arrayref($query, { Slice => {} });
print "Number of rows: " . @$numrows[0]->{rows} . "\n";

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