/redshift-guide

name: redshift-guide
description: "Amazon Redshift is NOT PostgreSQL — corrects PostgreSQL-derived LLM mistakes; covers Redshift-specific SQL, DDL, COPY/UNLOAD, system views, metadata discovery, and operational patterns. Applies ONLY when the task is about Redshift itself (cluster, Serverless workgroup, or Redshift SQL). Pushes back on: CREATE INDEX, string_agg, pg_catalog, text type, SERIAL, stl_query, LATERAL, RETURNING. Triggers on: Redshift SQL, Redshift CREATE TABLE, Redshift COPY/UNLOAD, slow Redshift query, Redshift permission denied, Redshift disk full, Redshift system views, QUALIFY, PIVOT, MERGE, Redshift Data API, Redshift WLM, concurrency scaling, Redshift resize, Redshift Spectrum external tables. Does NOT apply to (defer to that service's own skill): Amazon S3 storage/bucket policies, Athena or Glue queries/catalogs, data-lake or Iceberg work outside Redshift, Aurora, RDS, or DynamoDB — but S3/Glue ARE in scope for Redshift COPY, UNLOAD, or data-lake queries (external schemas/tables on S3)."
metadata:
  version: "1"

Amazon Redshift Guide

Redshift is NOT PostgreSQL (read first)

Redshift speaks PostgreSQL's wire protocol and shares much of its surface syntax, so LLMs assume PostgreSQL behavior carries over — it frequently does not. Divergences span system tables (`pg_catalog` is incomplete), DDL (no indexes, no sequences), functions (`string_agg`, `SUBSTR` on tables, leader-node-only functions), types (a `text` column becomes VARCHAR(256)), and comparison semantics (trailing blanks, unenforced constraints). **Assume divergence and verify against the reference below — do not answer from PostgreSQL habit.** Common PostgreSQL→Redshift divergences are in `references/redshift-sql-syntax.md`.

**Works best with** the [AWS MCP server](https://docs.aws.amazon.com/aws-mcp/) — it runs the AWS CLI and Redshift Data API calls below in a sandboxed, audit-logged environment. All guidance here is plain AWS CLI and SQL and works without it.

STEP 0: Serverless or Provisioned?

Establish this before answering — APIs, system tables, and capabilities differ. Take it from the question when it says which one; **ask** when it does not. `SELECT version()` does not identify it.

• **Serverless** — identified by a *workgroup* (and namespace). Data API calls take

`--workgroup-name`; the user says "workgroup"/"Serverless".

• **Provisioned** — identified by a *cluster*. Data API calls take

`--cluster-identifier`; the user says "cluster".

| Target | System Views | Credentials API | |---|---|---| | **Provisioned** | `SYS_`, all `SVV_` + `STL_`, `STV_`, `SVL_`, `SVCS_` (single-AZ only — disabled on Multi-AZ) | `redshift:GetClusterCredentials` | | **Serverless** | `SYS_` + a subset of `SVV_` ONLY (no `STL`/`STV`/`SVL`/`SVCS`) | `redshift-serverless:GetCredentials` |

Critical Facts

• **SHOW commands are the primary metadata interface** — SHOW DATABASES, SHOW SCHEMAS, SHOW TABLES, SHOW COLUMNS, SHOW TABLE, SHOW VIEW. Do NOT default to pg_catalog or information_schema. → **Load `references/redshift-sql-metadata.md` for metadata/discovery questions and any "relation does not exist" report** — it has the diagnostic flow.
• **`SYS_` views are the preferred system views** — they work everywhere. `STL_`, `STV_`, `SVL_`, and `SVCS_` are provisioned single-AZ only, and some `SVV_` views are unsupported on Serverless. → **Load `references/redshift-sql-metadata.md` for any system-view or monitoring question.**
• **`sys_load_error_detail`** for COPY debugging (not `stl_load_errors`, which is provisioned single-AZ only).
• **DATEADD/DATEDIFF** — unit-first argument order: `DATEADD(day, -30, GETDATE())`, `DATEDIFF(day, start, end)`.
• **APPROXIMATE COUNT(DISTINCT col)** — Redshift-specific, ~2% error, much faster than exact COUNT(DISTINCT) on large datasets.
• **MERGE ... REMOVE DUPLICATES** — simplified dedup when source and target have identical schemas.
• **COPY should use IAM_ROLE** (the namespace role, not the caller role) + supports MANIFEST for explicit file lists + MAXERROR for error tolerance.
• **`SUBSTR()` is leader-node-only** — works on literals but errors on table columns (`SUBSTR() function is not supported (Hint: use SUBSTRING instead)`). Use `SUBSTRING()` on columns.
• **UNIQUE / PRIMARY KEY / FOREIGN KEY are informational only** — NOT enforced (duplicate rows are accepted with no error). Optimizer hints; enforce integrity in the application or via MERGE. `NOT NULL` IS enforced.
• **`SHOW VIEW <schema.name>`** returns the definition of a regular view, materialized view, or late-binding view. MV freshness: `SVV_MV_INFO` (`is_stale`).
• **`TOP N` and `LIMIT N` both work** (`TOP N PERCENT` does not). A `text` column becomes `VARCHAR(256)` — use `VARCHAR(max)` or explicit length.
• **Iceberg tables use `CREATE TABLE ... USING ICEBERG`** (not `STORED AS ICEBERG`, not `TABLE_FORMAT=ICEBERG`).
• **Datashares support read and write operations** — consumers can write once the producer grants write privileges. Treat "permission denied" on a datashare write as a **missing grant**, not an unsupported operation. → **Load `references/redshift-sql-metadata.md` for requirements and limits.**

Safety Guardrails

**BLOCK:** DROP DATABASE, DELETE without WHERE, publicly-accessible=true, GRANT ALL ON ALL **WARN then confirm:** RESIZE, RESTORE, VACUUM on large tables, ALTER PASSWORD, WLM config change **Confirm:** CREATE, GRANT specific, COPY, UNLOAD

Security Considerations

Apply these defaults when generating anything that connects, loads, or exports. Details are in the reference files noted.

• **In transit:** the Data API is HTTPS-only. For JDBC/ODBC set the `require_ssl`

parameter and connect with `sslmode=verify-full` so the server certificate is checked.

• **At rest:** keep cluster/namespace encryption enabled, and add

`ENCRYPTED KMS_KEY_ID '<arn>'` to `UNLOAD` — it writes query results to S3, outside Redshift's own encryption. → `references/redshift-sql-ddl-copy.md`

• **Creden