Loading Data into Snowflake: Stages, COPY INTO, Schema Detection and Error Recovery

Part 4 of my Snowflake learning series. Parts 1–3 covered architecture, objects and SQL. Now we get data in and out: stages, file formats, PUT/GET, COPY INTO, load metadata, error handling, INFER_SCHEMA, MATCH_BY_COLUMN_NAME, and unloading.

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1. Loading overview

Snowflake loads data from files that sit in a stage. The standard bulk path:

local files / cloud bucket
          │   PUT (local only)
          ▼
   ┌─────────────┐     COPY INTO <table>      ┌─────────────┐
   │    STAGE    │ ─────────────────────────▶ │    TABLE    │
   │ (files)     │ ◀───────────────────────── │             │
   └─────────────┘     COPY INTO <stage>      └─────────────┘
          │   GET (internal only)
          ▼
     local files

COPY INTO runs on a virtual warehouse, so bulk loads consume credits. It processes many files in parallel (one file per thread), so file count and size matter for speed.

2. Setup and sample data