Question

我有三个表，我需要在第一个表中搜索，它没有任何结果，然后搜索到第二个表，依此类推......！

这是我的代码：

// connecting to database
$stm1 = $this->dbh->prepare(" select * from table1 where col = :name; ");
$stm1->bindValue(":name", $name, PDO::PARAM_STR);
$stm1->execute();
$which_table = "table1";

// the result of searching into table1 is zero, then search into table2
if (!$stm1->rowCount()) {
    $stm2 = $this->dbh->prepare(" select * from table2 where col = :name; ");
    $stm2->bindValue(":name", $name, PDO::PARAM_STR);
    $stm2->execute();
    $which_table = "table2";

    // the result of searching into table2 is zero, then search into table3
    if (!$stm2->rowCount()) {
        $stm3 = $this->dbh->prepare(" select * from table3 where col = :name; ");
        $stm3->bindValue(":name", $name, PDO::PARAM_STR);
        $stm3->execute();
        $which_table = "table3";

        // the result of searching into table3 is also zero
        if (!$stm3->rowCount()) {
            $which_table = 'none of them';
        }
    }
}

我的代码也可以运行，但它很慢，我如何优化它并使其更快？如您所见，有三个独立的查询和多个if语句..如何减少它们？一般来说，我如何改进该代码？我可以使用pure-sql吗？

Answer 1

我的代码也可以运行，但它很慢，我如何优化它并使其更快？

为列col

添加索引

顺便说一句，您可以在查询中添加limit 1。它会帮助你在表格中有数以万计的值来匹配

Answer 2

如果您的代码很慢，那么您可能只需要索引：

create index idx_table1_col on table1(col);
create index idx_table2_col on table2(col);
create index idx_table3_col on table3(col);

使用索引，您还可以将查询短语作为单个语句，假设表中的列相同：

select t1.*
from table1 t1
where t1.col = :name
union all
select t2.*
from table2 t2
where t2.col = :name and
      not exists (select 1 from table1 t1 where t1.col = :name)
union all
select t3.*
from table3 t3
where t3.col = :name and
      not exists (select 1 from table1 t1 where t1.col = :name) and
      not exists (select 1 from table2 t2 where t2.col = :name);

这是一个更复杂的查询，但您的代码只需要一个查询。并且，对于索引，它应该非常快。

如果搜索到表A的结果为零，如何搜索表B.

2 个答案: