example override get merge query

example_override_get_merge_query.sql

{% macro default__get_merge_sql(target, source, unique_key, dest_columns, predicates) -%}
    {%- set predicates = [] if predicates is none else [] + predicates -%}
    {%- set dest_cols_csv = get_quoted_csv(dest_columns | map(attribute="name")) -%}
    {%- set update_columns = config.get('merge_update_columns', default = dest_columns | map(attribute="quoted") | list) -%}
    {%- set sql_header = config.get('sql_header', none) -%}


    {% if unique_key %}
        {% if unique_key is sequence and unique_key is not mapping and unique_key is not string %}
            {% for key in unique_key %}
                {% set this_key_match %}
                    IFNULL(CAST(DBT_INTERNAL_SOURCE.{{ key }} AS STRING), "null") = IFNULL(CAST(DBT_INTERNAL_DEST.{{ key }} AS STRING), "null")
                {% endset %}
                {% do predicates.append(this_key_match) %}
            {% endfor %}
        {% else %}
            {% set unique_key_match %}
                IFNULL(CAST(DBT_INTERNAL_SOURCE.{{ key }} AS STRING), "null") = IFNULL(CAST(DBT_INTERNAL_DEST.{{ key }} AS STRING), "null")
            {% endset %}
            {% do predicates.append(unique_key_match) %}
        {% endif %}
    {% else %}
        {% do predicates.append('FALSE') %}
    {% endif %}

    {{ sql_header if sql_header is not none }}

    merge into {{ target }} as DBT_INTERNAL_DEST
        using {{ source }} as DBT_INTERNAL_SOURCE
        on {{ predicates | join(' and ') }}


    {% if unique_key %}
    when matched then update set
        {% for column_name in update_columns -%}
            {{ column_name }} = DBT_INTERNAL_SOURCE.{{ column_name }}
            {%- if not loop.last %}, {%- endif %}
        {%- endfor %}
    {% endif %}

{% endmacro %}