Table Structure Conversion

DBConvert Streams automatically converts table structure between source and target when they use different engines or formats. This includes data types, indexes, foreign keys, and check constraints.

Structure conversion applies to both Load and CDC modes.

Supported conversion paths

Database ↔ database

• MySQL → PostgreSQL
• PostgreSQL → MySQL
• MariaDB → PostgreSQL
• PostgreSQL → MariaDB

Files / S3 → database

• CSV → MySQL / PostgreSQL
• JSON / JSONL → MySQL / PostgreSQL
• Parquet → MySQL / PostgreSQL

Database → files / S3

• MySQL / PostgreSQL → CSV, JSONL, or Parquet files (local or S3)

Structure options

Structure creation is controlled per-stream via the structureOptions object in the target spec. All options are booleans and default to true.

Set an option to false to skip that structure type. For example, disabling indexes on large tables can speed up the initial load — you can create them manually afterward.

API example

{
  "target": {
    "id": "conn_TARGET_ID",
    "spec": {
      "db": {
        "database": "target_db",
        "structureOptions": {
          "tables": true,
          "indexes": false,
          "foreignKeys": false,
          "checkConstraints": true
        }
      }
    }
  }
}

In the UI, the stream wizard Structure & Data step exposes these as checkboxes under the advanced section.

Data type mapping: MySQL → PostgreSQL

Types not listed above map to TEXT as a fallback.

Data type mapping: PostgreSQL → MySQL

Types not listed above map to TEXT as a fallback.

File source → database target

When the source is a local file or S3 object, DBConvert Streams uses DuckDB to infer the schema:

• Parquet: schema is read from the file metadata (column names, types, nullability)
• CSV: read_csv_auto() infers column names from headers and types from sampled values
• JSON / JSONL: read_json_auto() infers structure from the document fields

The inferred types use standard SQL names (VARCHAR, INTEGER, TIMESTAMP, etc.) and flow through the same MySQL or PostgreSQL type mapper described above. For example, a Parquet column typed as BIGINT maps to BIGINT on both MySQL and PostgreSQL targets through the normal conversion path.

Database source → file target

When the target is a local file directory or S3 bucket, DBConvert Streams maps database types to DuckDB staging types for export:

Types not listed above map to VARCHAR as a fallback.

Output format is determined by the target configuration:

All formats also support gzip and zstd compression. Parquet additionally supports snappy.

Default value conversion

DBConvert Streams also converts default values between database engines:

• MySQL → PostgreSQL: MySQL zero dates (0000-00-00) convert to NULL. Boolean defaults 0/1 convert to false/true.
• PostgreSQL → MySQL: PostgreSQL sequences (nextval()) are skipped. Boolean defaults true/false convert to 1/0. Type casts (::type) are removed.

Check constraint conversion

Check constraints are translated between SQL dialects:

• PostgreSQL → MySQL: ANY(ARRAY[...]) converts to IN(...). PostgreSQL functions like jsonb_typeof map to MySQL equivalents like JSON_TYPE.
• MySQL → PostgreSQL: MySQL functions like json_valid map to PostgreSQL equivalents like jsonb_typeof. Backtick identifiers convert to double quotes.

Related docs

• Database Structure Options
• Stream Configuration Guide
• Local Files
• S3-Compatible Storage
• MySQL Target Configuration
• PostgreSQL Target Configuration