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-- Drop the constraint if it exists
set @var=if((SELECT true FROM information_schema.TABLE_CONSTRAINTS WHERE
   CONSTRAINT_SCHEMA = DATABASE() AND
   TABLE_NAME        = 'bluebookfacts' AND
   CONSTRAINT_NAME   = 'fk_bb_log_facts' AND
   CONSTRAINT_TYPE   = 'FOREIGN KEY') = true,'ALTER TABLE bluebook DROP FOREIGN KEY fk_bb_log_facts', 'select 1');
prepare stmt from @var;
execute stmt;
deallocate prepare stmt;

<table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><a href="#L-1">1</a> <a href="#L-2">2</a> <a href="#L-3">3</a> <a href="#L-4">4</a> <a href="#L-5">5</a> <a href="#L-6">6</a> <a href="#L-7">7</a> <a href="#L-8">8</a> <a href="#L-9">9</a></pre></div></td><td class="code"><div class="highlight"><pre><span></span><span id="L-1"><a name="L-1"></a>-- Drop the constraint if it exists </span><span id="L-2"><a name="L-2"></a>set @var=if((SELECT true FROM information_schema.TABLE_CONSTRAINTS WHERE </span><span id="L-3"><a name="L-3"></a> CONSTRAINT_SCHEMA = DATABASE() AND </span><span id="L-4"><a name="L-4"></a> TABLE_NAME = &#39;bluebookfacts&#39; AND </span><span id="L-5"><a name="L-5"></a> CONSTRAINT_NAME = &#39;fk_bb_log_facts&#39; AND </span><span id="L-6"><a name="L-6"></a> CONSTRAINT_TYPE = &#39;FOREIGN KEY&#39;) = true,&#39;ALTER TABLE bluebook DROP FOREIGN KEY fk_bb_log_facts&#39;, &#39;select 1&#39;); </span><span id="L-7"><a name="L-7"></a>prepare stmt from @var; </span><span id="L-8"><a name="L-8"></a>execute stmt; </span><span id="L-9"><a name="L-9"></a>deallocate prepare stmt; </span></pre></div> </td></tr></table>