PostgreSQL/Greenplum/Netezza to dbt Model Conversion

Purpose

Transform PostgreSQL/Greenplum/Netezza DDL (views, tables, stored procedures) into production-quality dbt models compatible with Snowflake, maintaining the same business logic and data transformation steps while following dbt best practices.

When to Use This Skill

Activate this skill when users ask about:

Converting PostgreSQL/Greenplum/Netezza views or tables to dbt models
Migrating PostgreSQL stored procedures to dbt
Translating PostgreSQL syntax to Snowflake
Generating schema.yml files with tests and documentation
Handling PostgreSQL-specific syntax conversions (array expressions, CHAR padding, psql commands)

Task Description

You are a database engineer working for a hospital system. You need to convert PostgreSQL/Greenplum/Netezza DDL to equivalent dbt code compatible with Snowflake, maintaining the same business logic and data transformation steps while following dbt best practices.

Input Requirements

I will provide you the PostgreSQL DDL to convert.

Audience

The code will be executed by data engineers who are learning Snowflake and dbt.

Output Requirements

Generate the following:

One or more dbt models with complete SQL for every column
A corresponding schema.yml file with appropriate tests and documentation
A config block with materialization strategy
Explanation of key changes and architectural decisions
Inline comments highlighting any syntax that was converted

Conversion Guidelines

General Principles

Replace procedural logic with declarative SQL where possible
Break down complex procedures into multiple modular dbt models
Implement appropriate incremental processing strategies
Maintain data quality checks through dbt tests
Use Snowflake SQL functions rather than macros whenever possible

Sample Response Format

-- dbt model: models/[domain]/[target_schema_name]/model_name.sql
{{ config(materialized='view') }}

/* Original Object: [database].[schema].[object_name]
   Source Platform: PostgreSQL/Greenplum/Netezza
   Purpose: [brief description]
   Conversion Notes: [key changes]
   Description: [SQL logic description] */

WITH source_data AS (
    SELECT
        -- SERIAL converted to INTEGER (use IDENTITY in table)
        customer_id::INTEGER AS customer_id,
        customer_name::VARCHAR(100) AS customer_name,
        account_balance::NUMBER(18,2) AS account_balance,
        -- TIMESTAMPTZ converted to TIMESTAMP_TZ
        created_date::TIMESTAMP_TZ AS created_date
    FROM {{ ref('upstream_model') }}
),

transformed_data AS (
    SELECT
        customer_id,
        UPPER(customer_name)::VARCHAR(100) AS customer_name_upper,
        account_balance,
        created_date,
        CURRENT_TIMESTAMP()::TIMESTAMP_NTZ AS loaded_at
    FROM source_data
)

SELECT
    customer_id,
    customer_name_upper,
    account_balance,
    created_date,
    loaded_at
FROM transformed_data

## models/[domain]/[target_schema_name]/_models.yml
version: 2

models:
  - name: model_name
    description: "Table description; converted from PostgreSQL [Original object name]"
    columns:
      - name: customer_id
        description: "Primary key - unique customer identifier"
        tests:
          - unique
          - not_null
      - name: customer_name_upper
        description: "Customer name in uppercase"
      - name: account_balance
        description: "Current account balance; Foreign key to OTHER_TABLE"
        tests:
          - relationships:
              to: ref('OTHER_TABLE')
              field: OTHER_TABLE_KEY
      - name: created_date
        description: "Date the customer record was created"
      - name: loaded_at
        description: "Timestamp when the record was loaded by dbt"

## dbt_project.yml (excerpt)
models:
  my_project:
    +materialized: view
    domain_name:
      +schema: target_schema_name

Specific Translation Rules

dbt Specific Requirements

If the source is a view, use a view materialization in dbt
Include appropriate dbt model configuration (materialization type)
Add documentation blocks for a schema.yml
Add descriptions for tables and columns
Include relevant tests
Define primary keys and relationships
Assume that upstream objects are models
Comprehensively provide all the columns in the output
Break complex procedures into multiple models if needed
Implement appropriate incremental strategies for large tables
Use Snowflake SQL functions rather than macros whenever possible
Always cast columns with explicit precision/scale using ::TYPE syntax (e.g., column_name::VARCHAR(100), amount::NUMBER(18,2)) to ensure output matches expected data types
Always provide explicit column aliases for clarity and documentation

Performance Optimization

Suggest clustering keys if needed
Recommend materialization strategy (view vs table)
Identify potential performance improvements

PostgreSQL to Snowflake Syntax Conversion

Convert array expressions (<> ALL, = ANY) to Snowflake equivalents
Handle CHAR padding differences
Replace psql commands with SnowSQL equivalents
Convert distribution keys (Greenplum) to clustering keys
Handle string comparison behavior differences
Convert PL/pgSQL to Snowflake Scripting
Replace PostgreSQL-specific operators
Handle SERIAL/BIGSERIAL with IDENTITY

Key Data Type Mappings

| PostgreSQL | Snowflake | Notes | | ----------------------- | ---------------------- | ----------------------- | | INTEGER/INT/INT4 | INTEGER | | | BIGINT/INT8 | BIGINT | | | SMALLINT/INT2 | SMALLINT | | | SERIAL/BIGSERIAL | IDENTITY | Use AUTOINCREMENT | | NUMERIC/DECIMAL | NUMERIC | | | REAL/FLOAT4 | FLOAT | | | DOUBLE PRECISION/FLOAT8 | FLOAT | | | BOOLEAN/BOOL | BOOLEAN | | | CHAR/VARCHAR/TEXT | Same | | | BYTEA | BINARY | | | DATE | DATE | | | TIME/TIMETZ | TIME | Time zone not supported | | TIMESTAMP/TIMESTAMPTZ | TIMESTAMP/TIMESTAMP_TZ | | | INTERVAL | VARCHAR | | | JSON/JSONB | VARIANT | | | ARRAY | ARRAY | | | UUID | VARCHAR | |

Key Syntax Conversions

-- SERIAL -> AUTOINCREMENT
id SERIAL PRIMARY KEY -> id INT AUTOINCREMENT PRIMARY KEY

-- Array expressions
col <> ALL(ARRAY[1,2,3]) -> NOT ARRAY_CONTAINS(col, ARRAY_CONSTRUCT(1,2,3))
col = ANY(ARRAY[1,2,3]) -> ARRAY_CONTAINS(col, ARRAY_CONSTRUCT(1,2,3))

-- psql commands -> SnowSQL
\d table -> DESCRIBE TABLE table
\dt -> SHOW TABLES

-- generate_series -> TABLE(GENERATOR())
generate_series(1, 10) -> TABLE(GENERATOR(ROWCOUNT => 10))

-- NOW() -> CURRENT_TIMESTAMP
NOW() -> CURRENT_TIMESTAMP()

Common Function Mappings

| PostgreSQL | -------------------------- | COALESCE(...) | NULLIF(a, b) | NOW() | CURRENT_DATE | CURRENT_TIMESTAMP | DATE_TRUNC(unit, d) | EXTRACT(part FROM d) | TO_CHAR(d, fmt) | TO_DATE(s, fmt) | TO_NUMBER(s, fmt) | generate_series(a, b) | array_agg(col) | string_agg(col, delim) | SUBSTR(s, pos, len) | POSITION(s IN str) | REGEXP_REPLACE(...) | json_extract_path_text() | ::type cast | Snowflake | Notes | | ------------------------------------- | --------------- | | COALESCE(...) | Same | | NULLIF(a, b) | Same | | CURRENT_TIMESTAMP() | | | CURRENT_DATE() | Add parentheses | | CURRENT_TIMESTAMP() | Add parentheses | | DATE_TRUNC(unit, d) | Same | | EXTRACT(part FROM d) | Same | | TO_CHAR(d, fmt) | Same | | TO_DATE(s, fmt) | Same | | TO_NUMBER(s, fmt) | Same | | TABLE(GENERATOR(ROWCOUNT => b-a+1)) | | | ARRAY_AGG(col) | Same | | LISTAGG(col, delim) | | | SUBSTR(s, pos, len) | Same | | POSITION(s IN str) | Same | | REGEXP_REPLACE(...) | Same | | JSON_EXTRACT_PATH_TEXT() | Same | | ::type cast | Same |

Dependencies

List any upstream dependencies
Suggest model organization in dbt project

Validation Checklist

[] Every DDL statement has been accounted for in the dbt models
[] SQL in models is compatible with Snowflake
[] PostgreSQL-specific syntax converted (array expressions, CHAR padding, distribution keys)
[] All business logic preserved
[] All columns included in output
[] Data types correctly mapped
[] Functions translated to Snowflake equivalents
[] Materialization strategy selected
[] Tests added
[] SQL logic description complete
[] Table descriptions added
[] Column descriptions added
[] Dependencies correctly mapped
[] Incremental logic (if applicable) verified
[] Inline comments added for converted syntax

Related Skills

$dbt-migration - For the complete migration workflow (discovery, planning, placeholder models, testing, deployment)
$dbt-modeling - For CTE patterns and SQL structure guidance
$dbt-testing - For implementing comprehensive dbt tests
$dbt-architecture - For project organization and folder structure
$dbt-materializations - For choosing materialization strategies (view, table, incremental, snapshots)
$dbt-performance - For clustering keys, warehouse sizing, and query optimization
$dbt-commands - For running dbt commands and model selection syntax
$dbt-core - For dbt installation, configuration, and package management
$snowflake-cli - For executing SQL and managing Snowflake objects

Supported Source Database

| Database | Key Considerations | | ------------------------------------ | --------------------------------------------------------------------------------------------- | | PostgreSQL / Greenplum / Netezza | Array expressions (<> ALL, = ANY), CHAR padding differences, psql commands, distribution keys |

Translation References

Detailed syntax translation guides are available in the translation-references/ folder.

Copyright Notice: The translation reference documentation in this repository is derived from Snowflake SnowConvert Documentation and is © Copyright Snowflake Inc. All rights reserved. Used for reference purposes only.

dbt-migration-postgres