drop a table using precondition in liquibase

drop-table-with-precondition.xml

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog" xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.6.xsd">
  <changeSet author="mohitgoyal" id="20190304224600">
    <preConditions onFail="HALT">
        <sqlCheck expectedResult="0">select count(*) from customer</sqlCheck>
	</preConditions>
	<comment>Make sure that no data exists in the table before you drop it</comment>
    <dropTable tableName="customer"/>
  </changeSet>
</databaseChangeLog>