How to update declarative schema?

Question

Here is my initial schema.xml , and run setup:upgrade, a table will be created

<table name="custom_channelintegration_sync_data">
    <column xsi:type="int" name="batch_id" padding="10" unsigned="true" nullable="false" identity="true" comment="primary key"/>
    <column xsi:type="varchar" name="ref_id" nullable="true" comment="ref_id"/>
    <column xsi:type="tinyint" name="status" padding="2" unsigned="true" nullable="false" comment="0:problematic 1:ok" default="1"/>
    <column xsi:type="text" name="data" nullable="true" comment="original data"/>
    <column xsi:type="timestamp" name="create_time" default="CURRENT_TIMESTAMP" on_update="false" comment="create time"/>
    <column xsi:type="timestamp" name="update_time" default="CURRENT_TIMESTAMP" on_update="false" comment="update time"/>
    <column xsi:type="varchar" name="sku" nullable="true" comment="sku"/>
    <constraint xsi:type="primary" referenceId="PRIMARY">
        <column name="batch_id"/>
    </constraint>
    <constraint xsi:type="index" referenceId="CHANNEL_REF_ID_INDEX">
        <column name="ref_id"/>
    </constraint>
</table>

after the table is created, i want to add a column

<table name="custom_channelintegration_sync_data">
        <column xsi:type="int" name="batch_id" padding="10" unsigned="true" nullable="false" identity="true" comment="primary key"/>
        <column xsi:type="varchar" name="ref_id" nullable="true" comment="ref_id"/>
        <column xsi:type="varchar" name="marketplace" nullable="true" comment="marketplace"/>
        <column xsi:type="tinyint" name="status" padding="2" unsigned="true" nullable="false" comment="0:problematic 1:ok" default="1"/>
        <column xsi:type="text" name="data" nullable="true" comment="original data"/>
        <column xsi:type="timestamp" name="create_time" default="CURRENT_TIMESTAMP" on_update="false" comment="create time"/>
        <column xsi:type="timestamp" name="update_time" default="CURRENT_TIMESTAMP" on_update="false" comment="update time"/>
        <column xsi:type="varchar" name="sku" nullable="true" comment="sku"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="batch_id"/>
        </constraint>
        <constraint xsi:type="index" referenceId="CHANNEL_REF_ID_INDEX">
            <column name="ref_id"/>
        </constraint>
    </table>

except delete the table, and re-run the setup:upgrade, what is the normal procedure to upgrade table structure?

i'tried run

bin/magento setup:db-declaration:generate-whitelist --module-name=Custom_ChannelIntegration && bin/magento setup:upgrade

but there is an error

SQLSTATE[42000]: Syntax error or access violation: 1061 Duplicate key name 'CUSTOM_CHANNELINTEGRATION_SYNC_DATA_REF_ID', query was: ALTER TABLE `custom_channelintegration_sync_data` ADD INDEX `CUSTOM_CHANNELINTEGRATION_SYNC_DATA_REF_ID` (`ref_id`)

Answer 1

replace

<constraint xsi:type="index" referenceId="CHANNEL_REF_ID_INDEX">
            <column name="ref_id"/>
        </constraint>

by

<index referenceId="CHANNEL_REF_ID_INDEX" indexType="btree">
            <column name="ref_id"/>
        </index>

Answer 2

Unrelated to the topic directly, but i found it interresting to still show this here as a response to the comment

What is the meaning of btree ?

To illustrate it's just a data structure system that allows to store data in a balanced way (the depth of the tree is equal for all 'leaf node' ) and as a consequence to access these data faster cause you don't have to run threw hundreds of pointers to get the data you are looking for . I assume most of database works with btree for performance issue.