---
title: Primary Sources
description: Connect KTX to PostgreSQL, Snowflake, BigQuery, ClickHouse, MySQL, SQL Server, or SQLite.
---

KTX connects to your data warehouse or database to build schema context,
discover relationships, and execute semantic layer queries. Each connection is
defined in `ktx.yaml` under the `connections` key.

All connectors share these conventions:

- Sensitive values support `env:VAR_NAME` (read from environment) and
  `file:/path/to/secret` (read from file) references
- Connections are read-only; KTX never writes to your database
- Database ingest discovers tables, columns, types, and constraints
  automatically

## Connection field reference

Agents should prefer environment or file references over literal secrets.

| Field | Required | Applies to | Description |
|-------|----------|------------|-------------|
| `driver` | Yes | all connections | Connector driver such as `postgres`, `snowflake`, `bigquery`, `clickhouse`, `mysql`, `sqlserver`, or `sqlite` |
| `url` | One of the connection methods | URL-style connectors | Database URL, `env:NAME`, or `file:/path/to/secret` |
| `host`, `port`, `database`, `username`, `password` | One of the connection methods | PostgreSQL, MySQL, ClickHouse, SQL Server | Field-by-field connection values |
| `schema` or `schemas` | No | schema-aware warehouses | Single schema or list of schemas to scan |
| `context.queryHistory` | No | PostgreSQL, Snowflake, BigQuery | Enables query-history ingestion when the warehouse supports it |
| `path` | Yes for path-style SQLite | SQLite | Local SQLite database path or `env:NAME` reference |
| `max_bytes_billed` | No | BigQuery | Maximum bytes billed per query job |
| `job_timeout_ms` | No | BigQuery | BigQuery query job timeout in milliseconds |
| `project_id` | No | BigQuery | Optional local descriptor and mapping metadata; not used for BigQuery authentication |

## PostgreSQL

The most full-featured connector. Supports schema introspection, foreign key detection, column statistics, and query history via `pg_stat_statements`.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-postgres:
    driver: postgres
    url: env:DATABASE_URL
    schema: public
```

Or with individual fields:

```yaml title="ktx.yaml"
connections:
  my-postgres:
    driver: postgres
    host: localhost
    port: 5432
    database: analytics
    username: ktx_reader
    password: env:PG_PASSWORD
    schemas:
      - public
      - analytics
    ssl: true
```

### Authentication

| Method | Config |
|--------|--------|
| Password | `password: env:PG_PASSWORD` or `password: file:/path/to/secret` |
| Connection URL | `url: env:DATABASE_URL` |
| SSL | `ssl: true`, optionally `rejectUnauthorized: false` for self-signed certs |

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `pg_catalog` |
| Primary keys | Yes | Via `information_schema.table_constraints` |
| Foreign keys | Yes | Full constraint detection |
| Row count estimates | Yes | Via `pg_class.reltuples` |
| Column statistics | Yes | Requires `pg_read_all_stats` role |
| Query history | Yes | Via `pg_stat_statements` extension |
| Table sampling | Yes | `TABLESAMPLE SYSTEM` |

### Query history

PostgreSQL query history mines real query patterns from `pg_stat_statements`.
This helps KTX understand how your team actually queries the data.

**Requirements:**
- `pg_stat_statements` extension enabled
- `pg_read_all_stats` role granted to the KTX user

**Config options:**

```yaml
    context:
      queryHistory:
        enabled: true
        minExecutions: 5
        filters:
          dropTrivialProbes: true
```

### Dialect notes

- SQL generation uses `LIMIT/OFFSET` pagination
- Named parameters converted to positional (`$1`, `$2`, ...)
- Supports `COUNT(*) FILTER (WHERE ...)` for null analysis
- Full support for PostgreSQL types: `uuid`, `jsonb`, `timestamptz`, `numeric`, `text[]`, etc.

---

## Snowflake

Connects via the Snowflake SDK. Supports multi-schema scanning, RSA key authentication, and query-history configuration for Snowflake query history.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-snowflake:
    driver: snowflake
    account: xy12345
    warehouse: ANALYTICS_WH
    database: PROD
    schema_name: PUBLIC
    username: KTX_SERVICE
    password: env:SNOWFLAKE_PASSWORD
    role: ANALYST
```

For multiple schemas:

```yaml
    schema_names:
      - PUBLIC
      - ANALYTICS
      - STAGING
```

### Authentication

| Method | Config |
|--------|--------|
| Password | `password: env:SNOWFLAKE_PASSWORD` |
| RSA key pair | `authMethod: rsa`, `privateKey: file:~/.ssh/snowflake_key.pem`, optional `passphrase` |

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `INFORMATION_SCHEMA.TABLES` |
| Primary keys | Yes | Via table constraints |
| Foreign keys | No | Not available in Snowflake |
| Row count estimates | Yes | From `INFORMATION_SCHEMA.TABLES.ROW_COUNT` |
| Column statistics | No | — |
| Query history | Yes | Via `SNOWFLAKE.ACCOUNT_USAGE.QUERY_HISTORY` when enabled |
| Table sampling | Yes | — |

### Query history

Snowflake query history reads aggregated query-history templates from
`SNOWFLAKE.ACCOUNT_USAGE.QUERY_HISTORY` and feeds the same unified staged
artifact shape as Postgres and BigQuery.

```yaml
    context:
      queryHistory:
        enabled: true
        windowDays: 90
        minExecutions: 5
        filters:
          dropTrivialProbes: true
          serviceAccounts:
            patterns: ['^svc_']
            mode: exclude
        redactionPatterns: []
```

### Dialect notes

- All identifiers are uppercase by default (case-insensitive matching)
- Connection context set per query (`USE ROLE`, `USE WAREHOUSE`, `USE DATABASE`, `USE SCHEMA`)
- Parameter binding uses positional `?` placeholders
- Date values normalized to ISO 8601 strings

---

## BigQuery

Authenticates via GCP service account credentials. Supports multi-dataset scanning and query-history configuration for `INFORMATION_SCHEMA.JOBS_BY_PROJECT`.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-bigquery:
    driver: bigquery
    credentials_json: file:~/.config/gcloud/bq-service-account.json
    dataset_id: analytics
    location: US
```

For multiple datasets:

```yaml
    dataset_ids:
      - analytics
      - marketing
      - finance
```

### Authentication

| Method | Config |
|--------|--------|
| Service account JSON | `credentials_json: file:/path/to/key.json` |
| Environment variable | `credentials_json: env:BIGQUERY_CREDENTIALS_JSON` |

The project ID is extracted automatically from the service account JSON file.
If you set `project_id` in `ktx.yaml`, KTX treats it as local descriptor and
mapping metadata. The BigQuery connector still authenticates with the
`project_id` inside `credentials_json`.

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Including materialized views and external tables |
| Primary keys | No | — |
| Foreign keys | No | Not available in BigQuery |
| Row count estimates | Yes | From table metadata |
| Column statistics | No | — |
| Query history | Yes | Via region-scoped `INFORMATION_SCHEMA.JOBS_BY_PROJECT` when enabled |
| Table sampling | Yes | — |

### Query history

BigQuery query history reads aggregated query-history templates from
region-scoped `INFORMATION_SCHEMA.JOBS_BY_PROJECT` and feeds the same unified
staged artifact shape as Postgres and Snowflake.

```yaml
    context:
      queryHistory:
        enabled: true
        windowDays: 90
        minExecutions: 5
        filters:
          dropTrivialProbes: true
          serviceAccounts:
            patterns: ['@bot\\.']
            mode: exclude
        redactionPatterns: []
```

### Dialect notes

- Parameter binding uses named `@param` syntax
- Arrays flattened to comma-separated strings in results
- Location specified at query execution time
- Supports `max_bytes_billed` and `job_timeout_ms` limits from `ktx.yaml`

---

## ClickHouse

Connects over HTTP (port 8123) or HTTPS (port 8443). Supports the ClickHouse native type system including `Nullable`, `LowCardinality`, and `Array` wrappers.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-clickhouse:
    driver: clickhouse
    url: http://localhost:8123/analytics
```

Or with individual fields:

```yaml title="ktx.yaml"
connections:
  my-clickhouse:
    driver: clickhouse
    host: clickhouse.internal
    port: 8123
    database: analytics
    username: default
    password: env:CH_PASSWORD
    ssl: false
```

### Authentication

| Method | Config |
|--------|--------|
| Basic auth | `username` + `password` (HTTP basic auth) |
| No auth | Default user `default` with no password |
| HTTPS | Set `ssl: true` (uses port 8443 by default) |

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `system.tables`, engine-based detection |
| Primary keys | Yes | Via `system.columns` |
| Foreign keys | No | Not a ClickHouse concept |
| Row count estimates | Yes | Via `system.parts` aggregation |
| Column statistics | No | — |
| Query history | No | — |
| Table sampling | Yes | — |

### Dialect notes

- Parameter binding uses `{param:Type}` syntax (e.g., `{database:String}`)
- Detects views vs. tables by engine name (`View`, `MaterializedView`)
- Handles `Nullable(T)` and `LowCardinality(Nullable(T))` type wrappers
- Dictionary tables are excluded from scanning
- Results returned in JSONCompact or JSONEachRow format

---

## MySQL

Standard MySQL/MariaDB connector with full foreign key support and schema introspection.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-mysql:
    driver: mysql
    url: env:MYSQL_DATABASE_URL
```

Or with individual fields:

```yaml title="ktx.yaml"
connections:
  my-mysql:
    driver: mysql
    host: mysql.internal
    port: 3306
    database: analytics
    username: ktx_reader
    password: env:MYSQL_PASSWORD
    ssl: true
```

### Authentication

| Method | Config |
|--------|--------|
| Password | `password: env:MYSQL_PASSWORD` or `password: file:/path/to/secret` |
| SSL | `ssl: true` or `ssl: { rejectUnauthorized: false }` |
| URL parameters | `?ssl=true` or `?sslmode=required` in connection URL |

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `INFORMATION_SCHEMA.TABLES` |
| Primary keys | Yes | Via `KEY_COLUMN_USAGE` |
| Foreign keys | Yes | Via `REFERENTIAL_CONSTRAINTS` |
| Row count estimates | Yes | From `TABLE_ROWS` (InnoDB estimate) |
| Column statistics | No | — |
| Query history | No | — |
| Table sampling | Yes | Uses `RAND()` filter |

### Dialect notes

- Parameter binding uses positional `?` placeholders
- Uses `LIMIT X OFFSET Y` for pagination
- Single database per connection (no multi-schema)
- Supports 20+ MySQL types including `enum`, `json`, `datetime`, `decimal`
- Table comments extracted with InnoDB metadata prefix stripping

---

## SQL Server

Connects to Microsoft SQL Server and Azure SQL. Supports multi-schema scanning with `dbo` as the default schema.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-sqlserver:
    driver: sqlserver
    url: env:SQLSERVER_DATABASE_URL
```

Or with individual fields:

```yaml title="ktx.yaml"
connections:
  my-sqlserver:
    driver: sqlserver
    host: sql.internal
    port: 1433
    database: Analytics
    username: ktx_reader
    password: env:MSSQL_PASSWORD
    schema: dbo
    trustServerCertificate: true
```

For multiple schemas:

```yaml
    schemas:
      - dbo
      - analytics
      - staging
```

### Authentication

| Method | Config |
|--------|--------|
| SQL Server auth | `username` + `password` |
| Encrypted connection | Always enabled, `trustServerCertificate: true` for self-signed |

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `INFORMATION_SCHEMA.TABLES` |
| Primary keys | Yes | Via `TABLE_CONSTRAINTS` and `KEY_COLUMN_USAGE` |
| Foreign keys | Yes | Via `REFERENTIAL_CONSTRAINTS` |
| Row count estimates | Yes | Via `sys.dm_db_partition_stats` |
| Column statistics | No | — |
| Query history | No | — |
| Table sampling | Yes | — |
| Nested analysis | No | — |

### Dialect notes

- Parameter binding uses `@paramName` syntax
- Row limiting uses `SELECT TOP N * FROM (query) AS ktx_query_result`
- Encryption is always required; certificate validation is optional
- Multi-schema support with per-schema isolation

---

## SQLite

File-based connector using `better-sqlite3`. Ideal for local development, embedded analytics, or testing.

### Connection config

```yaml title="ktx.yaml"
connections:
  my-sqlite:
    driver: sqlite
    path: ./data/warehouse.sqlite
```

Path supports multiple formats:

```yaml
# Relative path (resolved against project directory)
path: ./warehouse.sqlite

# Absolute path
path: /var/data/analytics.db

# Home directory expansion
path: ~/data/warehouse.sqlite

# Environment variable
path: env:SQLITE_DB_PATH

# URL format
url: sqlite:///path/to/db.sqlite
```

### Authentication

No authentication required — SQLite is file-based. The file must be readable by the process running KTX.

### Features

| Feature | Supported | Notes |
|---------|-----------|-------|
| Tables & views | Yes | Via `sqlite_master` |
| Primary keys | Yes | Via `PRAGMA table_info()` |
| Foreign keys | Yes | Via `PRAGMA foreign_key_list()` (requires `PRAGMA foreign_keys = ON`) |
| Row count estimates | Yes | Exact count via `SELECT COUNT(*)` |
| Column statistics | No | — |
| Query history | No | — |
| Table sampling | Yes | — |
| Nested analysis | No | — |

### Dialect notes

- Synchronous query execution (no connection pooling)
- Parameter binding uses `:paramName` syntax
- Uses `LIMIT X OFFSET Y` for pagination
- SQLite type affinity system: `TEXT`, `NUMERIC`, `INTEGER`, `REAL`, `BLOB`
- Foreign key enforcement requires explicit `PRAGMA foreign_keys = ON`
- In-memory databases supported with `path: ":memory:"` (for testing)

## Common errors

| Error or symptom | Likely cause | Recovery |
|------------------|--------------|----------|
| Connection URL appears in git diff | A literal credential URL was written to `ktx.yaml` | Replace it with `env:NAME` or `file:/path/to/secret` and rotate exposed credentials |
| Database ingest returns no tables | Schema, database, or project filter is wrong, or the user lacks metadata permissions | Verify the schema list and grant metadata read permissions |
| Query history is empty | Query history extension or warehouse history view is unavailable | Enable the warehouse-specific history feature, then rerun `ktx ingest <connectionId> --query-history` or `ktx setup` |
| Column statistics are missing | Connector cannot access stats tables or the warehouse does not expose them | Grant stats permissions where supported; otherwise rely on fast schema context |
| Semantic query execution fails | Connection is missing, unreachable, or query execution is disabled | Run `ktx connection test <id>` and check the `ktx sl query` flags |