How to INSERT based on a condition?

问题

I have these INSERT query:

$db->prepare("INSERT INTO
              events (post_id, table_code, other_id, user_id, author_id, date_time )
              VALUES (?      , 15        , ?       , ?      , ?        , UNIX_TIMESTAMP()),
                     (?      , 15        , ?       , ?      , ?        , UNIX_TIMESTAMP())
")->execute(array($answer_id, $answer_id, $author_ques_id, $author_ques_id,
                  $answer_id, $answer_id, $author_ques_id, $author_ans_id));

As you see, query above inserts two rows into events table. Now I need to put a condition on the way of second row. I mean if $condition is true then inserts second rows, else it shouldn't insert second row. (first row always should be inserted).

Note: $condition always is containing a boolean value.

Well, how can I put that condition on the way of second row inserting?

回答1:

You could use a insert select statement like this:

$db
->prepare("INSERT INTO
             events (post_id, table_code, other_id, user_id, author_id, date_time )
             select ?, 15, ?, ?, ?, UNIX_TIMESTAMP()
              UNION ALL
             select ?, 15, ?, ?, ?, UNIX_TIMESTAMP()
               from (select 1) as a
              where 1=?
")->execute(array($answer_id, $answer_id, $author_ques_id, $author_ques_id,
                  $answer_id, $answer_id, $author_ques_id, $author_ans_id,
                  ($yourCondition?1:0) ));

回答2:

Whats wrong with doing it in 2 queries?

$query = $db->prepare("INSERT INTO
              events (post_id, table_code, other_id, user_id, author_id, date_time)
              VALUES (?, 15, ?, ?, ?, UNIX_TIMESTAMP())");

$query->execute(array($answer_id1, $answer_id1, $author_ques_id1, $author_ans_id1));

if ($condition)
    $query->execute(array($answer_id2, $answer_id2, $author_ques_id2, $author_ans_id2));

回答3:

You can build query string and values array before preparing and executing.

$query = "INSERT INTO
          events (post_id, table_code, other_id, user_id, author_id, date_time )
          VALUES (?, 15, ?, ?, ?, UNIX_TIMESTAMP())";
$values = array($answer_id, $answer_id, $author_ques_id, $author_ques_id);
if ($condition) {
    $query .= ",(?, 15, ?, ?, ?, UNIX_TIMESTAMP())";
    $values = array_merge($values, array($answer_id, $answer_id, $author_ques_id, $author_ans_id);
}
$db->prepare($query)->execute($values);

回答4:

Since the $condition is a php variable why not do it in PHP like so:

if ($condition === true) {
    $db->prepare($first_and_seccond_row);
} else {
    $db->prepare($first_row);
}

来源：https://stackoverflow.com/questions/37846754/how-to-insert-based-on-a-condition

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php

mysql

sql

pdo