有条件的2个表中的SQL查询

Question

I am trying to understand how a query from 2 tables linked via one common value is supposed to look like. Below my example based on the timezone record of my users.

Table: qci_users (table with all user details) Columns:

• ID
• Timezone

Table: timezones (all GMT timezone information) Columns:

• TimeZoneID
• GMTadjustment
• UseDaylightTime
• TimeZone
• Description

I now would like to query all of the above column values where qci_user.Timezone and timezones.TimeZone have the same value.

Code:

// get user timezone setting
$sql = ("SELECT TimeZoneID, GMTadjustment, UseDaylightTime, TimeZone, Description, qci_users.Timezone
FROM timezones
WHERE qci_users.Timezone = timezones.TimeZone");

$result = $db->query($sql) or die('<p>Query to get timezone data from timezones table failed: ' . mysqli_error($db) . '</p>');

while ($row = $result->fetch_array(MYSQLI_ASSOC)) {
    $id = $row['TimeZoneID'];
    $gmtAdjustment = $row['GMTadjustment'];
    $useDaylightTime = $row['UseDaylightTime'];
    $tz = $row['TimeZone'];
    $description = $row['Description'];
    $user_tz = $row['Timezone'];

    echo "<option timeZoneId=\"$id\" gmtAdjustment=\"$gmtAdjustment\" useDaylightTime=\"$useDaylightTime\" value=\"$user_tz\">$description</option>\n";
}

The query doesnt return any results, hence me wondering where I am going wrong here?

Thanks

Answer 1

You are missing a join condition. You probably intended this:

SELECT t1.TimeZoneID,
       t1.GMTadjustment,
       t1.UseDaylightTime,
       t1.TimeZone,
       t1.Description
FROM timezones t1
INNER JOIN qci_users t2
    ON t1.Timezone = t2.TimeZone

Answer 2

Try this

SELECT u.* ,t.* FROM qci_users u LEFT JOIN timezones t ON u.Timezone=t.TimeZoneID

This will help you

Thanks

Answer 3

Try this

SELECT usr.* ,tmz.*
  FROM qci_users AS usr JOIN timezones AS tmz ON usr.Timezone = tmz.TimeZone;