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POMySQL performance between multi join queries vs. using function
 

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    <p>I have a table which is named: <code>candidate_info</code> has three columns are <code>id_user</code>, <code>id_type</code> and <code>value</code>:</p> <ul> <li>id_type = 1 => Fullname</li> <li>id_type = 2 => Email</li> <li>id_type = 3 => Mailing Address</li> <li>id_type = 4 => Phone number</li> </ul> <p>to store user information:</p> <p>I consider two queries as below, it will combine from rows to columns:</p> <p>Form Original:</p> <pre><code>Id User | Id Type | Value 1 | 1 | John 1 | 2 | john@g.com 1 | 3 | Ho Chi Minh 1 | 4 | 123 2 | 1 | Ana 2 | 2 | ana@g.com 2 | 3 | New York 2 | 4 | 456 </code></pre> <p>To New:</p> <pre><code>Id User | Fullname | Email | Mailing_Address | Phone Number 1 | John | john@g.com | Ho Chi Minh | 123 2 | Ana | ana@g.com | New York | 456 </code></pre> <p><strong>1. First query:</strong></p> <pre><code>select c1.id_user, c1.value as fullname, c2.value as email, c3.value as mailing_address, c4.value as phone_number from candidate_info c1 left join candidate_info c2 ON c1.id_user = c2.id_user left join candidate_info c3 ON c1.id_user = c3.id_user left join candidate_info c4 ON c1.id_user = c4.id_user where c1.id_type = 1 and c2.id_type = 2 and c3.id_type = 3 and c4.id_type = 4; </code></pre> <p><strong>2. Second query</strong></p> <pre><code>select c.id_user, MAX(IF(c.id_type = 1, c.value, NULL)) as fullname, MAX(IF(c.id_type = 2, c.value, NULL)) as email, MAX(IF(c.id_type = 3, c.value, NULL)) as mailing_address, MAX(IF(c.id_type = 4, c.value, NULL)) as phone_number from candidate_info c where c.id_type in (1, 2, 3, 4) group by c.id_user </code></pre> <p>Which is better?</p> <p>Edit: Change <code>id_entry_field</code> to <code>id_type</code>, <code>join</code> to <code>left join</code> to make sense.</p>
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