PHP MySQL query data related issues-add where is not good, I do not know what is wrong

PHP MySQL Query data problem-plus where is not good, I do not know what is wrong
$query _cn = "Select Pestcide_trade_name from insecticide where company_name=bayer"; $q _result_cn = mysql_query ($query _cn );
while ($each _QUES_CN = mysql_fetch_row ($q _result_cn))
{
Print $each _ques_cn[0];
}

If I do not add where the above code $query _CN = "Select Pestcide_trade_name from Insecticide"; If you add it, the following warning will be reported.

Warning:mysql_fetch_row (): supplied argument is not a valid MySQL result resource in d:\apm_setup\htdocs\search.php on Li NE 33

Line 33 is the same while ($each _QUES_CN = mysql_fetch_row ($q _result_cn)). Thank you all first.

------Solution--------------------
$query _cn = "Select Pestcide_trade_name from insecticide where company_name= ' Bayer '";
------Solution--------------------
discuss

$query _cn = "Select Pestcide_trade_name from insecticide where company_name= ' Bayer '";

------Solution--------------------
... where company_name= ' $name ' ";

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